JP6529165B2 - Method of manufacturing powder alloy extruded material and method of manufacturing forged product - Google Patents

Description

  The present invention relates to a method for producing extruded materials of various metal powders such as aluminum alloys, and in particular, a high-strength metal powder alloy extruded material suitable for use in hot-pressing metal powder compacts, for example, for forging And a method of manufacturing a forged product using the extruded material.

  In recent years, the demand for fuel efficiency improvement in the automobile industry has increased the demand for weight reduction and functional enhancement of various members used in automobiles, such as pistons of engines. Therefore, for such a member, it is directed to use a lightweight aluminum material instead of a steel material or a cast iron material, and in particular, it has high temperature and high strength which can be used even in a severe environment such as a high temperature atmosphere. Forged materials made of aluminum powder alloys such as Si-based alloys are attracting attention.

  For producing this kind of aluminum powder alloy forging, as described in, for example, Patent Document 1, a rapidly solidified powder by an atomizing method or the like comprising an aluminum alloy (for example, an Al-Si alloy) having a predetermined composition. The resultant is compression-molded into a cylindrical shape into a powder billet, the billet is preheated to a required temperature, hot extrusion is performed, and the obtained extruded body is die-forged into a product shape.

  In order to obtain an extruded body with excellent surface quality by hot extrusion during such an aluminum powder alloy forging process, conventionally, the powder billet is preheated uniformly and at a relatively low temperature over its entire length. Extrusion is considered desirable. That is, when the material is excessively preheated to a high temperature and extruded, the crystallized material present in the grain boundary causes eutectic melting to peel off the crystal grains in the vicinity of the surface, for example, as shown in FIG. As shown in the figure, projections 22 (hereinafter referred to as "mushile") in the form of local peeling on the surface of the extruded material 20 may be generated, the surface roughness may be increased, or the surface roughness may be further increased. It is feared that the surface quality may be degraded such as being uneven depending on the place. Therefore, conventionally, for example, a powder billet having a length of about 1100 mm of a high-temperature high-strength Al-Si-based aluminum alloy is uniformly preheated to a relatively low temperature of about 250 to 270 ° C. and inserted into a container of an extruder. , Extrusion has been done.

  However, the deformation resistance of the powder billet at a low temperature is very high, so during extrusion of a powder billet preheated to a low temperature, the tip of the billet is first extruded and shaped as the extrusion proceeds The extrusion pressure increases rapidly. Therefore, by the time the rear end of the billet is extruded, the extrusion pressure may reach the limit value of the extruder, which may make extrusion impossible or difficult.

  Therefore, in consideration of extrudability, it is conceivable to perform extrusion by preheating the entire length of the powder billet to as high temperature as possible (for example, about 300 to 400 ° C.) within the range that does not impair the surface quality of the extruded material. . It is considered that since the deformation resistance is reduced by preheating to high temperature and extruding in this way, extruding can be performed relatively easily. However, even if the preheating temperature (the material heating temperature before extrusion) of the powder billet is below the upper limit that does not impair the surface quality of the extruded material, if the preheating temperature is close to the upper limit, Problems will arise.

  That is, the portion (middle portion) between the tip end portion and the rear end portion of the billet is not only surrounded by the container heated to a high temperature, but the front and rear end portions of the billet Since it continues to the end, there is no room for heat, so the friction heat between the extrusion die and the material during extrusion and the processing heat of the powder billet itself are stored in the middle part, and the material before extrusion starts The temperature rises to a temperature range higher than the temperature (preheating temperature). As a result, the temperature becomes higher than the upper limit temperature that does not impair the surface quality of the extruded material, and the surface roughness of the extruded material There are times when

  In addition, since the billet tip portion has little heat storage due to frictional heat with the die and processing heat, it does not become excessively hot during extrusion. Therefore, if the preheating temperature is appropriately set as described above, high quality surface conditions can be obtained for the tip of the extruded material. On the other hand, in the extrusion container, the rear end face of the powder billet is always in contact with the pressing plate (generally, a member not heated), so that the billet rear end is heated by the heat to the pressing plate. Elevated temperatures are avoided, and good surface quality can be exhibited.

  As described above, if the powder billet is extruded with high temperature and uniform preheating within a range that does not impair the surface quality of the extruded material, the leading end and the trailing end of the extruded material have excellent surface roughness. Although it is possible to obtain a large size, it is highly possible that the surface quality of the middle part is significantly reduced by the temperature rise. Thus, if the extruded material in which the portion where the surface quality is lowered is used as it is for die forging in the next step as a product, the material flow near the surface of the forged material is disturbed at the time of die forging and the flow is not smooth. As a result, there are problems in product quality such as deterioration of mechanical characteristics, variation in mechanical characteristics, and deterioration of surface quality of extruded material, and a problem that yield of good products decreases. is there.

  With regard to the extruded material where there is a point where the surface quality has deteriorated as described above, it is also carried out that the surface is subjected to cutting (face grinding) and then used for die forging in the next step. For example, the productivity may be lowered, the cost may be increased, and the material yield may be decreased. Therefore, it is strongly desirable not to add such a facing process as much as possible.

  In addition, in hot extrusion of a green compact billet such as an aluminum alloy, the heating temperature (preheating temperature) of the billet before insertion into the container is determined according to the temperature change in the extrusion direction of the billet during extrusion. A so-called tapered heating method is known in the prior art that provides a temperature gradient (taper) that changes in direction.

  For example, in patent document 2, the taper-heating method which heats the temperature of the back side in the extrusion direction of a billet lower than the temperature of the front side is described as a prior art. The tapered heating method described in Patent Document 2 is considered to be a method for preventing the temperature on the rear side of the billet from becoming higher than that on the front side due to accumulation of processing heat generation during extrusion. However, the influence of heat removal from the rear end face (the face in contact with the pressing plate) of the billet is not considered at all. Therefore, when the taper heating method described in Patent Document 2 is applied as it is, there is a possibility that the temperature of the rear end decreases excessively, and the extrusion of the rear end may become difficult or impossible.

In addition, the above-described taper heating method fundamentally has the following problems.
That is, in a material having a high thermal conductivity, such as an aluminum alloy, one compact billet is actually inserted into the extrusion container immediately after heating even if it is heated so as to give a temperature gradient in its length direction. Before the start of extrusion, the heat conduction inside the billet advances the homogenization of the temperature in the longitudinal direction, and the temperature gradient becomes smaller. As a result, the effect of the targeted temperature gradient There is a problem that can not be obtained enough.

Patent No. 4185364 Unexamined-Japanese-Patent No. 2004-25266

  The present invention has been made against the background described above, and it is possible to heat the powder billet of metal powder such as aluminum alloy powder and the like to produce an extruded material by extruding hot without impairing the extrudability. A method for producing a powder alloy extruded material capable of reliably and stably obtaining an extruded material having an excellent surface quality over the entire length, and a method for producing a forged product having a good surface quality using the extruded material Is an issue.

  As a result of various experiments and studies to solve the above-mentioned problems, the present inventors conducted various experiments and studies, and as a result, a powder billet to be inserted into an extrusion container and extruded is one from the front end to the rear end in the extrusion direction. Instead of extruding as a billet, extruding as a billet in a state of being divided into three or more pieces in the length direction (extrusion direction), and assuming that, the billet on the leading end side of the extrusion direction and the billet on the rear end side To be heated (preheated) so as to be higher than the billet (intermediate billet) sandwiched between them, and loaded into the extrusion container; conversely, the preheating temperature of the middle billet is at the front end and the rear end It has been found that the above problems can be solved at once by preheating to a lower temperature than each billet and loading into an extrusion container, and the present invention has been made.

  In the above description, the billet is described as being extruded as a billet in a “divided” state in the longitudinal direction (extrusion direction), but the “divided” is described here for the sake of explanation. Of course, the present invention is not limited to cutting one green powder billet obtained by compression molding into three or more pieces. That is, "divided" means that three or more may be provided in the state of being disposed in the container. Therefore, for example, the case where three or more billets are individually compression-molded and the resulting three or more billets are loaded in series in one container is also included.

Specifically, the method for producing a powder alloy extruded material according to the basic aspect (first aspect) of the present invention is
A preheating step of preheating three or more powder billets formed by compression molding of metal powder;
And extruding the hot-extruded three or more green compact billets into the extrusion container of the hot extruder in series along the extrusion direction;
In the preheating step, a green compact billet and the first green compact billet disposed in the extrusion direction top end side arranged in the direction of extrusion leading-edge side in the extrusion container in said extrusion step, these top it is characterized in that than one or more of the green compact billet sandwiched disposed between the tip side pressure powder billet and the top rear side pressure powder billet is heated to a high temperature.
Here, the numbers in the respective descriptions of the above three or more green compact billets, one green compact billet, and one or two green compact billets mean the number of green compact billets.
Also, in the following, the one powder billet disposed on the most end side in the extrusion direction in the extrusion container may be referred to as a powder billet for tip, and disposed on the most end side in the extrusion direction in the extrusion container One of the pressed powder billets is sometimes referred to as a back end powder billet, and further, for one or more powder billets placed between them, for intermediate use It may be called a green compact billet.

  As described above, in the present embodiment, it is assumed that the powder billet loaded in the container is not loaded as one continuous billet, but loaded in series in the container in a state of being divided into three or more. There is. Here, when each billet (each divided billet) is preheated to a different temperature and then inserted into the container, each divided billet is treated independently before loading each billet into the container, Furthermore, while each billet is loaded into the container for extrusion, the contact boundary between the divided billets functions as a resistance to heat transfer. Therefore, the temperature uniformity due to the heat transfer in the lengthwise direction (extrusion direction) of the entire billet is prevented. That is, if one billet is preheated to have a temperature gradient in its length direction and the one billet is extruded (as in the prior art), there is a decrease or elimination of the temperature gradient after heating It is possible to avoid the occurrence. In other words, it is possible to maintain the targeted temperature difference.

  Here, in the case of the billet of the ingot material instead of the billet of the green compact, if the billet is loaded in series in the container in a state of being divided into three or more as described above, each billet is divided even if it is hot extruded. There is a possibility that it will not be sufficiently joined and integrated, and it will be easily broken at the boundary even with a slight impact, and in particular if the extruded material is further forged such as die forging to make it a product, it may not be able to withstand forging. high. Therefore, in the case of billets made of molten material, it is not common sense to insert and push the billets in a divided state into a container.

  On the other hand, in the case of the powder billet targeted by the present invention, the powder particles are entangled with each other between the contact surfaces of the divided billet by plastic deformation during extrusion, and a surface oxide film such as Al alloy is easily formed. Even if it is a metal, the surface oxide film of the powder particle is broken between the contact surfaces of the divided billet by the plastic deformation during extrusion due to the unevenness by the powder particle on the surface of the powder compact, and the new surface is exposed. The diffusion proceeds sufficiently to obtain a firmly bonded one as an extruded material. As a result, subsequent forging can be sufficiently tolerated. Therefore, extruding as a split billet is only effective in powder billets.

Of the three or more split billets placed in the container, cutting-edge side in the extrusion direction, dividing the billet (tip for compact billets, compact billet rear end) of the top rear side, in the meantime The powder billet for the leading end and the powder billet for the trailing end are heated on the surface of the extruded material by heating (preheating) to a higher temperature than the one or more billets (intermediate green powder billet) to be sandwiched. Good extrudability can be ensured without loss of quality. That billet cutting-edge side, since less frictional heat and working heat generation accumulation of the die during extrusion, a possibility is small that the temperature rise during the extrusion, the deterioration of the surface quality of the order extrudate excessively increase in temperature It is possible to satisfy both the extrudability and the surface quality by preheating to a suitable high temperature, since this can be avoided. The split billets rearmost side, during the extrusion, usually in contact with the押盤unheated, since the heat removal to the side of押盤, be avoided that heat due working heat generation is thermal storage , less risk of elevated temperature during the extrusion with it, can be avoided that lowers the surface quality of the order extrudate excessively rise in temperature, by preheated to moderate high temperatures, most distal end As in the case of the divided billet, it is possible to satisfy both the extrudability and the surface quality.

On the other hand, a green compact billet for between medium is already no escape of the heat due to work-induced heat as mentioned, it is usual to temperature rise by the heat storage. However, for the intermediate for compact billet preheat temperature, most distal end side, by keeping the temperature lower than the split billet rearmost side, without impairing the surface quality of the extruded material even if a temperature rise in the extrusion At the same time as suppressing the temperature to a certain degree, it becomes possible to secure good extrudability. That is, the temperature rise obtained during extrusion is predicted, and a temperature (high temperature) at which good extrudability can be secured within a range that does not impair the surface quality of the extruded material is subtracted from the predicted temperature rise. By setting the preheating temperature, it is possible to secure the extrudability and secure the surface quality in a state where the temperature rises during the extrusion.

  In the method for producing a powder alloy extruded material according to the second aspect of the present invention, in the method for producing a powder alloy extruded material according to the first aspect, the metal powder is an aluminum alloy powder. is there.

  Here, the aluminum alloy has a high thermal conductivity, and therefore, in the case of a green compact billet formed by compression molding of the aluminum alloy powder, in particular, a temperature gradient in the lengthwise direction in one billet as in the prior art described above. If hot extrusion is carried out in the form of one compacted powder billet, heat gradient within the billet will be reduced, so that the effect of temperature gradient can not be expected. Sex is high. That is, it is difficult to achieve both the extrudability and the securing of the surface quality. However, according to the method of the present invention, the heat is carried out by dividing the powder billet loaded in the container into three or more pieces as described above and appropriately setting the preheating temperature of each billet according to the position in the container. Even in the case of an aluminum alloy having a high conductivity, it has become possible to achieve both the extrudability and the securing of the surface quality.

Furthermore, in the method for producing a powder alloy extruded material according to the third aspect of the present invention, in the method for producing a powder alloy extruded material according to the second aspect,
Wherein the preheating step, the green compact billet and compact billets which are located closest to the rear end side is arranged on the most distal end side of the extrusion direction of the extrusion container heated to 350-420 ° C., these advanced lateral pressure The method is characterized in that one or more green powder billets placed between the powder billet and the rear end side green powder billet are heated to 230 ° C to 300 ° C.

If an aluminum alloy target, the extrusion direction of the compact billets and compact billets (green compact billet tip for-rear, which is located closest to the rear end side is arranged on the most distal end side of the extrusion container ) the by preheated to a temperature in the range of 350-420 ° C., can be satisfied both the extrudability and extruded material surface quality at up tip-top rear portion.
In addition, the intermediate portion is extruded due to the temperature rise during the extrusion by preheating the one or more green powder billets (intermediate green powder billet) disposed in the middle to a temperature within the range of 230 to 300 ° C. As well as ensuring the properties, good surface quality can be secured even in anticipation of temperature rise during extrusion.
Note that green compact billet compact billet disposed on the outermost distal side and top rear end of the extrusion direction, more preferably be preheated within the range of from 370 to 400 ° C. arranged desirable and the intermediate More preferably, it is desirable to heat in the range of 250-270 degreeC. By setting the preheating temperature of each green compact billet within such a temperature range, the extrudability and the surface quality can be reconciled more reliably and stably.

Furthermore, in the method for producing a powder alloy extruded material according to the fourth aspect of the present invention, in the method for producing a powder alloy extruded material according to any of the second and third aspects,
In the extrusion step, the extrusion container is heated such that the inner surface temperature of the extrusion container is 300 to 400 ° C.

  In hot extrusion, not only is the powder billet preheated before being loaded into the extrusion container, it is also possible to heat the extrusion container itself when loading the powder billet into the container or during extrusion. It is effective to prevent the temperature drop of the powder billet and to secure good extrudability. For that purpose, it is appropriate to heat a container to the temperature within the range of 270-400 degreeC, when targeting aluminum alloy.

Furthermore, in the method for producing a powder alloy extruded material according to the fifth aspect of the present invention, in the method for producing a powder alloy extruded material according to any one of the first to fourth aspects,
In the extrusion step, the inner surface temperature of the extrusion container is controlled individually at the leading end portion, the rear end portion, and the middle portion thereof in the extrusion direction.

  In this way, it is more preferable to divide the region into three or more regions according to the position in the extrusion direction and to control each region to an appropriate temperature, in order to achieve both the extrudability and the surface quality.

In the method for producing a powder alloy extruded material according to the sixth aspect of the present invention, in the method for producing a powder alloy extruded material according to the fifth aspect,
The metal powder is an aluminum alloy powder,
In the extruding step, the inner surface temperature of the extruding container is a temperature in the range of 330 to 400 ° C. at the leading end portion and the trailing end portion in the extruding direction, and a temperature in the range of 270 to 330 ° C. at the middle portion of the extruding direction. To heat the extrusion container.

  Thus, by heating the container to a temperature within the above-mentioned range by region, the entire billet is extruded while maintaining the surface condition uniformly and favorably without impairing the extrudability. It is possible to obtain a uniform and good extruded material over the entire length.

In the method for producing a powder alloy extruded material according to the seventh aspect of the present invention, in the method for producing a powder alloy extruded material according to any one of the first to sixth aspects,
The thermal conductivity of the green powder billet is characterized by being in the range of 0.01 W / m · K or more and 1 W / m · K or less.

  When the thermal conductivity of the green powder billet is within the above range, the effects of the present invention can be obtained more reliably.

  Furthermore, in the method for producing a forged product according to the eighth aspect, the powder alloy extruded material obtained by the method for producing a powder alloy extruded material according to any one of the first to seventh aspects is further subjected to die forging To obtain.

  When the alloy powder extruded body with inferior surface quality is die forged, the smooth flow of the material in the vicinity of the surface of the forged material (extruded material) during die forging is impeded, and the mechanical properties of the forged product are inferior, Characteristics may vary, and there is also a concern that the surface quality of the forged product may become inferior. However, die forging is performed using the extruded material according to the first to sixth aspects. If done, because the surface quality of the extruded material itself is good, it is possible to stably obtain a forged product which has good mechanical properties and little variation, and further, good surface quality.

  According to the method for producing a powder alloy extruded material of the present invention, the powder billet of metal powder such as aluminum alloy powder is heated and extruded hot to produce an extruded material. The extruded material with excellent surface quality can be obtained reliably and stably. In addition, if the extruded material is die-forged to produce a forged product, it is possible to obtain a forged product having good mechanical properties, less variation thereof, and good surface quality.

BRIEF DESCRIPTION OF THE DRAWINGS It is a flowchart which shows an example of the whole process of the process of manufacturing a powder alloy forged product, applying the manufacturing method of the powder alloy extruded material of this invention. When extruding a powder billet by the method for producing a powder alloy extruded material of the present invention, it is a schematic view showing an example of a state in which the billet is loaded in the extrusion container. When extruding a powder billet by the method for producing a powder alloy extruded material of the present invention, it is a schematic view showing another example of a state in which the billet is loaded in the extrusion container. When extruding a powder compact billet by the method for producing a powder alloy extruded material of the present invention, it is a schematic view showing still another example of a state in which the billet is loaded in the extrusion container. It is a schematic diagram which shows the generation | occurrence | production condition of a muzzle as an example of the surface defect at the time of carrying out the hot extrusion of the powder billet by a prior art.

  Hereinafter, an embodiment of a method for producing a powder alloy extruded material of the present invention will be described in detail with reference to the drawings. Note that the embodiments shown below are merely examples, and it goes without saying that the present invention is not limited to these embodiments.

<Target metal>
The type of metal and the component composition to be targeted in the present invention are not particularly limited, and a metal suitable for obtaining an extruded material by hot extrusion of a powder billet obtained by compression molding of a metal powder All applicable, and in addition, alloys, typically Al alloys, suitable for the process of die forging the extruded body to produce a powder alloy forged product are suitable. And it can apply suitably to the high temperature high strength alloy of Al-Si system also among Al alloys.
The above-mentioned high temperature high strength Al-Si alloy contains, for example, by mass%, Si: 8 to 20%, Fe: 3 to 10%, Cu: 2 to 7%, Mg: 0.5 to 3% An alloy in which the balance is Al and unavoidable impurities is preferred. Besides, for example, an alloy containing, by mass%, Al: 5 to 11%, Zn: 0.05 to 0.1% and the balance being Mg and unavoidable impurities is also applicable.

  The method of the present invention is preferably applied to a material having a thermal conductivity of 0.01 W / m · K or more and 1 W / m · K or less in the state of a green compact billet. That is, the method of the present invention is intended to solve the problem in the case of using a material having a relatively high thermal conductivity (for example, a material having a thermal conductivity of 0.01 W / m · K or more), If the thermal conductivity is excessively high, the early heat transfer between the green powder billets during extrusion may not sufficiently exert the effect of providing the temperature difference to each divided billet according to the method of the present invention. is there. By the way, in the powder billet of the above-mentioned high temperature high strength Al-Si alloy, for example, the powder billet having a relative density of about 60 to 90%, the thermal conductivity is about 0.01 to 1 W / m · K. The thermal conductivity of other aluminum alloy compact billets is similar.

<Overall process>
FIG. 1 shows an outline of an example of the entire production process when producing a powder alloy extruded material of the present invention, for example, to produce an Al alloy powder forged product. Therefore, the outline of the whole process will be described first with reference to FIG.

As shown in FIG. 1, a metal powder, for example, an Al alloy powder, is compression molded according to a conventional method to obtain three or more green compact billets for extrusion (compression molding step S1). That is, after the extrusion process, the green compact billet rear end disposed at the distal end for the compact billets and bottom rear end is arranged on the most distal end side of the extrusion direction of the extrusion container, sandwiched therebetween And one or more intermediate powder billets placed in the middle.

Next, each green compact billet is preheated (preheating step S2). In this preheating step, the front end green powder billet, the rear end green powder billet, and one or more intermediate green powder billets are heated to different temperatures. That is, the front and rear billets are preheated to relatively high temperatures, and the intermediate powder billet is preheated to relatively low temperatures.
Subsequently, these three or more powder billets are loaded in series along the extrusion direction into the same extrusion container. At this time, a green powder billet preheated to a relatively high temperature is disposed at the leading end and the rear end in the extrusion direction, and a green powder billet preheated to a relatively low temperature is disposed in the middle thereof. In this state, the three or more green compacts in the container are pressurized in the series direction to perform hot extrusion (hot extrusion step S3). In extrusion, it is also effective to heat the extrusion container itself. In that case, it is desirable to heat the container from the stage prior to placing the powder billet into the extrusion container.

  The extruded material obtained by the hot extrusion is subjected to die forging into a product shape (die forging step S4) to make a final product, for example, a piston for an automobile engine. Depending on the type of Al alloy, it goes without saying that heat treatment may be carried out after extrusion or after die forging, and when die forging is carried out, it may be carried out combining the die forging and heat treatment.

  In the process of FIG. 1, the extruded material is further subjected to die forging to obtain a product shape, but in some cases, die forging is not performed, and it is acceptable to produce the extruded material as it is.

  Further, the details of each step as described above will be described.

<Compression molding process>
The Al alloy powder, which is the starting material, is compression-molded into a cylindrical or disk-like shape suitable for extrusion, to obtain a green compact billet. Although the manufacturing method of Al alloy powder to be used is not specifically limited, It is desirable to apply the method of obtaining fine powder efficiently, such as the atomizing method. The particle size of the powder to be subjected to compression molding is, for example, preferably about 30 to 70 μm in average particle size. The compression molding may be performed cold or hot. Furthermore, the density of the green compact is not limited, but it is generally about 60 to 90% in relative density.

  Here, three or more compacted powder billets to be arranged in series in the extrusion container are one or more relatively long billets obtained in one compression molding, three or more in the lengthwise direction with a cutter or the like. Alternatively, three or more green compact billets may be compression molded so as to be individually short and have the same diameter. In any case, before the next preheating step, three or more compacted powder billets of the same diameter, that is, a front end and rear end compacted powder billet, and one or more intermediate compacted powder billets And prepare. The lengths (length in the extrusion direction) of the green powder billets do not have to be the same.

<Preheating>
In the preheating step, the front end green powder billet, the rear end green powder billet, and one or more intermediate green powder billets are heated to different temperatures. That is, the front and rear billets are preheated to relatively high temperatures, and the intermediate powder billet is preheated to relatively low temperatures. Although the specific heating temperature in the preheating of each green powder billet varies depending on the component of the metal powder, in the case of an Al alloy, for example, the aforementioned high-temperature high strength Al alloy of the Al-Si system, the powder billet for tip and back The end-use powder billet is preferably heated to a temperature in the range of 350 to 420 ° C, and the intermediate-use powder billet is preferably heated to a temperature in the range of 230 to 300 ° C.

  When the heating temperature of the front end / rear end green compact billet is less than 350 ° C., the deformation resistance is large, and the extrusion pressure limit may be exceeded to make extrusion difficult or impossible. On the other hand, if the temperature exceeds 420 ° C., the surface roughness of the extruded material increases, for example, to Rz 0.1 μm or more, the surface roughness varies, and further, the surface of the extruded material may have a muffle, etc. It may cause deterioration. If the temperature is in the range of 350 to 420 ° C., both the extrudability and the surface quality of the extruded material can be satisfied for the front end and rear end powder billets. More preferably, it is desirable to heat the front and rear end green compact billets to a temperature within the range of 370 to 400 ° C.

  For the intermediate powder billet, it is desirable to preheat to a temperature in the range of 230-300 ° C. If the preheating temperature of the intermediate powder billet is less than 230 ° C., the temperature range where good extrudability can be obtained can not be reached even in anticipation of temperature rise due to heat storage during extrusion, deformation resistance becomes large, and extrusion pressure limit Exceeding this may make extrusion difficult or impossible. On the other hand, if the temperature exceeds 300 ° C., the surface roughness of the extruded material increases, for example, to Rz 0.1 μm or more due to temperature rise due to heat storage during extrusion, or the surface roughness varies, and further, the surface of the extruded material becomes muddy. And may cause deterioration of the surface quality. It is desirable that the preheating temperature of the intermediate powder billet be set to a temperature in the range of 250 to 270 ° C., more preferably.

  The heating means for preheating is not particularly limited, and for example, any heating means such as heating in a heating furnace in which a powder billet is inserted into a heating furnace, or induction heating can be applied.

<Loading of billet into extrusion container>
The preheated three or more green powder billets are loaded in series into the extrusion container of the extruder. In FIG. 2, in the extrusion container 3 of the extruder 1 for backward extrusion, three green powder billets, that is, a green powder billet 9F for the leading end, a green powder billet 9R for the rear end, and an intermediate green compact The state which loaded billet 9M in series (the state just before the extrusion start) is shown. Further, in FIG. 3, in the extrusion container 3 in the extruder 1 for backward extrusion, four green powder billets, that is, a green powder billet 9F for the leading end, a green powder billet 9R for the rear end, and two middle The green powder billets 9M ₁ and 9M ₂ are loaded in series. The front end powder billet 9F is in contact with the extrusion die 5, and the rear end powder billet 9R is in contact with the pressing plate 8 and surrounded by the extrusion container 3, respectively, and the intermediate pressure billet 9M ( 9M ₁ and 9M ₂ ) are surrounded by the extrusion container 3 without contacting other members. Reference numeral 7 denotes an extrusion ram for advancing and retracting the extrusion die 5.
In addition, as an extrusion method, not only backward extrusion but forward extrusion can also be applied. The loading condition of each green powder billet in the case of forward extrusion is shown in FIG.

  Here, immediately after preheating, it is desirable that the time to load three or more green compact billets into the extrusion container and to start the extrusion be as short as possible. Specifically, it is preferable to set the time from the time immediately after preheating (for example, the time of taking out the billet from the heating furnace when the green compact billet is preheated by the heating furnace) to 180 seconds or less before starting the extrusion. If this time is too long and exceeds 180 seconds, the temperature (particularly the surface temperature) of the preheated green compact billet may be lowered, and the extrudability may be deteriorated. In addition, if the time for which the front and rear billets are in contact with the middle billet is long before the start of extrusion, the temperature difference between the front and rear billets and the middle billet becomes small, which causes a temperature difference. There is a possibility that the effect by providing the may not be sufficiently exhibited. If the time from the point immediately after preheating to the start of extrusion is within 180 seconds, the temperature drop of the preheated powder billet is reduced, and the temperature difference between the front and rear billets and the intermediate billet To maintain both extrudability and surface quality.

<Hot extrusion process>
If three or more green powder billets are loaded in series in the extrusion container and hot extrusion is performed, the contact parts of the green powder billets are not in contact with the molten materials, as plastic deformation occurs. Since the surfaces of the green compacts are in contact with each other, as described above, it is possible to obtain an integrated extruded material which is strongly joined by plastic deformation by extrusion.
During extrusion, as described above, the temperature tends to rise in the middle part, but since the intermediate billet sets the preheating temperature to a low temperature, the temperature rise during extrusion causes a decrease in surface quality. Is avoided. And if the preheating temperature of the billet for intermediate use is in a moderate low temperature range (for example, within the range of 230 to 300 ° C., preferably within the range of 250 to 270 ° C. for aluminum alloy), extrudability is ensured by temperature rise during extrusion. While maintaining good surface quality.
On the other hand, although the temperature rise may be small at the front end portion and the rear end portion, or the temperature may decrease slightly, the front end and rear end powder billets set the preheating temperature to a high temperature, It is possible to maintain good extrudability. And, if the preheating temperature of the billet for front end / rear end is in an appropriate high temperature range (for example, in the range of 350 to 420 ° C., preferably 370 to 400 ° C. for aluminum alloy), it is good while avoiding the surface quality deterioration Good extrudability.
The directionality of extrusion may be either backward extrusion (FIG. 2, FIG. 3) or forward extrusion (FIG. 4) as described above.

<Container heating>
In hot extrusion, each green powder billet (preheated green powder billet) is loaded into the container while the extrusion container is heated to a predetermined temperature in advance, and the container is heated during extrusion as well. It is desirable to continuously maintain the inner surface temperature of the container at a predetermined temperature. By extruding while maintaining the container at a predetermined temperature in this manner, the temperature of the powder billet preheated and loaded into the container is excessively increased due to processing heat generation or frictional heat generation, and the extruded material is extruded. It is possible to prevent the surface quality of the container from being impaired, and the temperature drop by the heat removal to the inner surface of the container to lower the extrusion property.

Here, the container inner surface temperature (hereinafter referred to as "container temperature") maintained during extrusion by container heating is preferably a temperature range of 270 to 400 ° C when the target is an aluminum alloy.
The higher the container temperature, the better the extrudability, and even the difficult-to-process materials can be easily extruded. However, if the container temperature exceeds 400 ° C., there is a concern that the temperature of the powder billet will rise due to heat absorption from the container and the surface quality of the extruded material will be impaired. On the other hand, if the container temperature is low, heat removal from the powder billet to the container lowers the temperature of the powder billet, and the effect of improving the surface quality of the extruded material becomes large, but conversely, the extrudability decreases significantly. In particular, when the container temperature is less than 270 ° C., the tendency becomes strong. Therefore, from these viewpoints, it is desirable that the container temperature be in a temperature range of 270 to 400 ° C.
In addition, the means to heat a container is not specifically limited, For example, an appropriate heating means, such as induction heating and electrical resistance heating, may be applied.

<Container temperature area control>
As described above, it is desirable that the container temperature be in the range of 270 to 400 ° C. However, it is further possible to divide into three or more regions according to the position in the extrusion direction and control each region to an appropriate temperature. It is preferable for the coexistence of extrudability and surface quality.
That is, as shown in, for example, FIG. 2 or FIG. 3, the extrusion container 3 has, in the extrusion direction, a front end region 3F, a rear end region 3R, and one or more intermediate regions 3M between them. Divided into Here, the front end region 3F is a region corresponding to the front end green powder billet 9F, the rear end region 3R is a region corresponding to the rear end green powder billet 9R, and the middle region 3M is an intermediate green powder The region corresponds to the body billet 9M (9M ₁ , 9M ₂ ). Then, the front end region 3F and the rear end region 3R of the extrusion container 3 are relatively heated to a high temperature, and the middle region 3M is relatively heated to a low temperature.

  Here, when the container temperature area control is performed, when the metal powder is an Al alloy, for example, the above-described high-temperature high-strength Al-Si alloy, the front end region 3F and the rear end region 3R of the extrusion container have their inner surface temperatures Is preferably in the range of 330 to 400.degree. C., and the middle region 3M of the extrusion container is preferably heated so that the inner surface temperature is in the range of 270 to 330.degree. The reason is as follows.

  That is, if the temperature of the front end region 3F of the extrusion container is lowered to about 300 ° C., the peak pressure at the time when the front end of the extruded material is pushed out from the die may increase, making extrusion difficult. On the other hand, if the temperature of the rear end region 3R of the extrusion container is lowered to about 300 ° C., the heat dissipation to the billet is reduced, and the deformation resistance of the billet may be increased to make extrusion difficult. And if the front end region 3F and the rear end region 3R of the extrusion container are heated within the range of 330 to 400 ° C., good extrudability can be achieved without impairing the surface quality of the front end and rear end of the extruded material. It becomes possible to secure.

  On the other hand, even if the billet temperature (preheating temperature) is low, there is no room for heat escape during extrusion, so the temperature of the central portion of the billet may be higher than the heat absorption from the inner surface of the container and the surface condition may be degraded. If the temperature of the middle region 3M of the extrusion container is set to a relatively low temperature, for example, about 270 to 330 ° C., even the billet middle portion corresponding to the middle region 3M can be extruded without losing the surface quality.

<Die forging>
The alloy powder extruded material obtained as described above may be machined as it is to obtain a product, but high temperature high strength such as picitone for automobile engines mainly targeted in the present invention is required In the case of a product to be processed, it is general to subject the extruded material to die forging to obtain a product shape or a shape close to it (product formed material shape). As die forging at this time, in the case of the Al-Si based alloy as described above, hot die forging is preferable, but depending on the alloy type, cold die forging is also acceptable. In some cases, forging may be repeated twice or more, and in that case, hot die forging and cold die forging may be combined. Furthermore, depending on the alloy type, heat treatment may be performed after extrusion or die forging. These forging conditions and heat treatment conditions are not particularly limited, and may be the same as conventional ones.

  Hereinafter, examples of the present invention will be described together with comparative examples.

Experimental Example 1
A molten metal of an Al-Si based aluminum alloy containing 12% by mass, Fe: 7%, Cu: 3%, Mg: 1% by mass%, the balance being Al and unavoidable impurities is produced by a conventional method The resultant was rapidly solidified by atomization to obtain an Al alloy powder having an average particle size of 50 μm. The Al alloy powder was subjected to hot compression molding by hot press molding to obtain a cylindrical green compact billet having a relative density of about 70%, a diameter of 203 mm, and a length of 1000 mm. The green powder billet was divided into three in the length direction (extrusion direction) to obtain a front end billet and a rear end billet each having a length of 250 mm and an intermediate billet having a length of 500 mm.

The billets thus obtained were preheated to different heating temperatures by the billet for the leading end and the billet for the rear end, and the billet in the middle portion, respectively, in a heating furnace. Each heated billet was taken out, loaded and transported on a loading platform, temporarily placed on a transfer machine using a billet holding jig, and transferred to a billet loader. When transferring to the billet loader, the high temperature billet (tip billet and rear end billet) is first transferred to the front and back sides of the billet loader, and then the low temperature billet (intermediate billet) is billet loader Transferred to the middle part of. The three billets transferred to the billet loader were loaded by a pusher into the extrusion container of the rear extruder. Therefore, among the three billets, the front end billet and the rear end billet are disposed at both ends of the container in the extrusion direction, and the middle billet is disposed at the middle. Moreover, also about the container, the front-end part and the back end part and the intermediate part were heated to different heating temperature by induction heating. Here, as a heating temperature of each part of the container, the container front end portion and the rear end portion were heated to 350 ° C., and the container middle portion was heated to 300 ° C.
Thereafter, hot extrusion was performed by backward extrusion, and the extrudability and surface roughness of the extruded material were evaluated. The results are shown in Table 1.
In Table 1, ○ indicates that extrudable and surface roughness Rz is less than 0.1 μm, Δ indicates that extrudable but surface roughness Rz is 0.1 μm or more, and × indicates extrusion. In the case where the surface quality of the extruded material is bad at the visual level, such as impossibility or generation of a mussel on the surface, respectively, is shown.

As shown in Table 1, when the preheating temperatures of the front end billet and the rear end billet were lower than 370 ° C., the extrusion pressure limit was reached because the deformation resistance was large, and extrusion became impossible.
On the other hand, when the preheating temperatures of the front end billet and the rear end billet were in the range of 370 to 400 ° C., the deformation resistance decreased, the extrusion property was improved, and the extrusion became possible.

  On the other hand, if the preheating temperature of the intermediate billet becomes higher than 300 ° C, although extrusion is possible, the billet temperature is further raised during extrusion due to the increase in heat storage capacity, and the surface roughness of the extruded material middle portion It was confirmed that the surface quality was lost.

  Then, the billet for leading end and trailing end is preheated to a temperature within the range of 370 to 400 ° C., and the intermediate billed powder billet is preheated to a temperature within the range of 250 to 300 ° C. It was confirmed that an extruded material having good surface quality was obtained while maintaining good extrudability over the entire length.

<Experimental Example 2>
As a comparative example for the present invention, compression molding is carried out in the same manner as in Experimental Example 1 using a rapidly solidified powder by an atomizing method consisting of an aluminum alloy of the same composition as that used in Experimental Example 1. Powder billets of the same dimensions were made. The green powder billet was divided into three in the longitudinal direction (extrusion direction) in the same manner as in Experimental Example 1 to obtain the same tip billet for rear end and the billet for rear end, and the middle billet.
When preheating each billet using a heating furnace, only the front end billet is heated to 370 ° C., the middle billet and the rear end billet are heated to 270 ° C., and the same is loaded into the extrusion container, and heat is applied. Extrusion was performed.
In the case of this experimental example 2, although the extrusion could be performed without problems from the initial stage to the middle stage of the extrusion, the extrusion pressure increased toward the end of the extrusion and reached the pressure limit before the end of the extrusion, making the extrusion impossible.

<Experimental Example 3>
As a comparative example for the present invention, compression molding is carried out in the same manner as in Experimental Example 1 using a rapidly solidified powder by an atomizing method consisting of an aluminum alloy of the same composition as that used in Experimental Example 1. Powder billets of the same dimensions were made. The green powder billet was divided into three in the longitudinal direction (extrusion direction) in the same manner as in Experimental Example 1 to obtain the same tip billet for rear end and the billet for rear end, and the middle billet.
When preheating each billet using a heating furnace, only the billet for the rear end is heated at 370 ° C., the billet for the middle and the billet for the tip are heated to 270 ° C., and loaded into the extrusion container as described above Hot extrusion was performed.
In the case of this experimental example 3, the pressure rise was remarkable from the beginning of the extrusion, and when the tip of the extruded material was extruded from the die, the pressure limit was reached and the extrusion became impossible.

DESCRIPTION OF SYMBOLS 1 ... Extruder, 3 ... Extrusion container, 5 ... Die, 7 ... Extrusion ram, 8 ... Press disc, 9F ... Powder billet for tips, 9M, 9M ₁ , 9M ₂ ... Powder billet for middle, 9R ... Powder billet for rear end, 20 ... extruded material.

Claims (8)

A preheating step of preheating three or more powder billets formed by compression molding of metal powder;
And extruding the hot-extruded three or more green compact billets into the extrusion container of the hot extruder in series along the extrusion direction;
In the preheating step, a green compact billet and the first green compact billet disposed in the extrusion direction top end side arranged in the direction of extrusion leading-edge side in the extrusion container in said extrusion step, these top method of producing a powder alloy extruded material, characterized in that interposed between heating temperature higher than the one or more compact billet is positioned between the tip side pressure powder billet and the top rear side pressure powder billet .   The method for producing a powder alloy extruded material according to claim 1, wherein the metal powder is an aluminum alloy powder. Wherein the preheating step, the green compact billet and compact billets which are located closest to the rear end side is arranged on the most distal end side of the extrusion direction of the extrusion container heated to 350-420 ° C., these advanced lateral pressure The powder alloy according to claim 2, characterized in that one or more powder billets placed between the powder billet and the end-side powder billet are heated to 230 to 300 ° C. Method of manufacturing extruded material.   4. The powder alloy extruded material according to claim 2, wherein the extrusion container is heated so that the inner surface temperature of the extrusion container is 270 to 400 ° C. in the extrusion step. Production method.   The temperature control of the inner surface temperature of an extrusion container is independently carried out in the said extrusion process in the front-end | tip part of an extrusion direction, a back end part, and those intermediate parts. The manufacturing method of the powder alloy extrusion material as described in any one of Claims. In the above-mentioned extrusion process, the inner surface temperature of the extrusion container becomes a temperature within the range of 330 to 400 ° C. at the leading end and the rear end of the extrusion direction, and becomes a temperature within the range of 270 to 330 ° C. at the middle part of the extrusion direction The method for producing a powder alloy extruded material according to claim 5, wherein the extrusion container is heated as described above.
  The powder alloy according to any one of claims 1 to 6, wherein the thermal conductivity of the powder billet is in the range of 0.01 W / m · K or more and 1 W / m · K or less. Method of manufacturing extruded material.   A method for producing a forged product, wherein the powder alloy extruded material obtained by the method according to any one of claims 1 to 7 is further subjected to die forging to obtain a forged product.

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