JPH0565573B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention is an aluminum casting with excellent pressure resistance suitable for use in mechanical parts such as engine parts of automobiles, ships, vehicles, etc., which require strict pressure leak resistance. - silicon-magnesium alloy,
Or it relates to an aluminum-silicon-magnesium-copper alloy. (Prior art) Aluminum-silicon-magnesium alloys generally represented by JIS standards AC4A and AC4C,
Aluminum-silicon-magnesium-copper alloys, represented by AC4D, AC8A, AC8B, AC8C, etc., have good castability and can be heat-treated to provide excellent mechanical properties and pressure resistance. It is widely used as an aluminum alloy for casting engine parts such as pistons, hydraulic parts, safety parts, and other mechanical parts in automobiles, ships, vehicles, etc. (Problem to be solved by the invention) However, in this type of aluminum alloy, when the iron content in the alloy increases, the pressure resistance of the casting rapidly decreases, and pressure leakage often occurs in cast parts. This was a problem because there was a risk of causing defects such as. According to the inventors' research, this phenomenon is almost never observed when the iron content in the alloy is 0.2% or less, but when it exceeds this, it gradually becomes seen here and there, and when it exceeds 0.4%, it tends to become more common. was found to be significant. By the way, generally in foundries, from the viewpoint of saving resources and costs, alloy ingots are made by adding a large amount of scrap material to the primary alloy ingot called new ingot, and secondary alloy ingots are mixed mainly by scrap material. is used in large quantities, but a large amount of iron is usually mixed in as an impurity in the scrap material, so foundries use this type of alloy for the above purpose, especially for strict pressure resistance. When used in engine parts such as pistons for automobiles and ships that require high performance, the iron content as an impurity must be reduced.
It is necessary to adjust the amount to the lowest possible amount of 0.4% or less, and the alloy blending operation for this purpose is extremely troublesome.
Moreover, this is not preferable because it causes an increase in costs. In addition, in cast parts with complex shapes, the increase in iron content in the alloy tends to cause poor pressure resistance in thick-walled parts that solidify slowly. However, it was necessary to conduct solidification, which was troublesome and required special ingenuity in the design of the mold and the casting method. The present inventors investigated the cause of the decrease in pressure resistance of castings due to increased iron content regarding the above-mentioned problems in aluminum-silicon-magnesium alloys or aluminum-silicon-magnesium-copper alloys for castings, and found that these systems When the iron content in the alloy increases, when casting from the molten alloy, the iron in the alloy component becomes aluminum,
Reacts with silicon to form acicular aluminum-silicon
Iron-based compounds are crystallized, and these acicular compounds rapidly increase near the final solidification part of the molten metal, such as the thick center of the casting, and develop into a cross-linked shape and become coarse, inhibiting the subsequent sufficiency of the molten metal in this area. It was found that crack-like shrinkage cavities and aggregates of fine continuous linear shrinkage cavities are likely to occur, which causes deterioration of the pressure resistance of the casting. Figure 1 a, b, c, and d are representative examples of experimentally illustrating the relationship between the iron content in the alloy and the occurrence of internal shrinkage cavities in aluminum-silicon-magnesium-copper alloy castings. . During the experiment, silicon 6.5%, magnesium 0.3%, and copper were used, each with varying iron content in the alloy.
A molten aluminum alloy containing 3.0% was cast into a Tater mold, and the cross section of the ingot was color checked to check for shrinkage cavity defects. As can be seen from Figure 1, the iron content in the alloy is
In the case of 0.05% alloy a, solidification is completed with the bottom of the solidification shrinkage, which is the final solidified part of the ingot, being rounded and almost no shrinkage cavity defects are observed. % of alloy B, thin, small crack-like shrinkage cavities and many fine linear shrinkage cavities appear at the bottom of solidification shrinkage, and alloy C with iron content of 0.36%, alloy d with iron content of 0.65%, and alloy B with iron content of 0.65%. As the size increases further, the number and size of these nest defects at the bottom of the solidification shrinkage expand, and they become partially in communication with each other. According to the inventors' experiments, this relationship is common not only to alloys with the above compositions but also to aluminum-silicon-magnesium alloys and aluminum-silicon-magnesium-copper alloys for practical casting of all compositions. Therefore, in actual castings made from these alloys, the interconnected cavities developed inside these castings are easily exposed to the surface due to surface processing after casting, and liquids and gases are easily exposed to the surface. Since it is distributed to the outside via these defects, when castings made of such alloys are used for pressure-resistant parts, the pressure resistance is impaired. In view of the above-mentioned facts, the present inventors have conducted extensive research to overcome these problems, and as a result,
When adding an appropriate amount of calcium to an aluminum-silicon-magnesium or aluminum-silicon-magnesium-copper alloy that contains a large amount of iron, it is important to avoid the formation of interconnected cracks found in the casting during alloy casting. It has been found that the occurrence of shrinkage cavities and fine linear shrinkage cavities can be greatly reduced, and therefore the pressure resistance of castings can be further improved. (Means for Solving the Problems) That is, the present invention contains 4 to 11% silicon, 0.1 to 2% magnesium, and 0.001 to 0.01% calcium, and further contains up to 5% copper and 1 manganese as required. % or less, 3% or less of nickel, and the balance consists of aluminum and impurities, and the iron content of the impurities is more than 0.4% and less than 0.8%.It is an aluminum alloy for casting with excellent pressure resistance. (Function) According to the present invention, the iron content in the alloy is 0.8
%, by adding 0.001 to 0.01% calcium, this kind of alloy casting can be improved in conventional practical aluminum-silicon-magnesium alloy castings or aluminum-silicon-magnesium-copper alloy castings. Without interfering with other unique and excellent properties, it is possible to prevent a decrease in pressure resistance caused by the occurrence of internal shrinkage cavities of a special shape based on the iron content in the alloy, and the strength, toughness, etc. are improved. Therefore, even if scrap metal or secondary alloy metal with a high iron content is used in a foundry, etc., it can be used to produce engine parts for automobiles, ships, etc. without having to take any care to adjust the iron content in the mixed metal. It is extremely effective because it allows casting of cast products that require strict pressure resistance. Next, the effects and reasons for limitations of each additive element in the alloy of the present invention will be explained. Addition of 4 to 11% silicon has the effect of strengthening the alloy matrix and improving flowability, shrinkage, prevention of casting cracks, etc. Below 4.0%, the effect is small, and above 11%, it improves the toughness and heat resistance of the casting. Significantly reduces impact resistance. Addition of 0.1 to 2% magnesium has the effect of precipitating Mg ₂ Si in the alloy structure by heat-treating the casting and strengthening the alloy matrix; below 0.1%, the effect is small, and above 2%, the effect is weak. elongation is small,
Castability also deteriorates. Addition of less than 5% copper will result in heat treatment.
Although it imparts significant strength to alloy castings through the aging effect, addition of 5% or more reduces elongation and impairs toughness. Addition of 1% or less of manganese and 3% or less of nickel imparts heat resistance to the casting, but
If the amount of manganese added exceeds 1%, the added manganese reacts with aluminum and silicon in the alloy components and iron contained as an impurity, crystallizing coarse needle-shaped compounds of aluminum-manganese-silicon-iron system, resulting in castings. Moreover, if the amount of nickel added exceeds 3%, coarse aluminum-nickel compounds are formed, which also causes a decrease in toughness. In the present invention, silicon,
Aluminum-silicon containing magnesium and, if necessary, copper, manganese, and nickel
Magnesium-based or aluminum-silicon
In magnesium-copper alloys, calcium
0.001 to 0.01% of calcium is added, but as mentioned above, calcium content in the above range may cause shrinkage cavities in alloy casting products due to the iron content in these two types of alloys. It has the effect of preventing a decrease in pressure resistance due to an increase in molten alloy, and if the content is less than 0.001%, the effect will be small, and if it exceeds 0.01%, the fluidity of the molten alloy will decrease and it will not be able to form a casting. You will want to create healthy products that will not cause hot spots etc. Therefore, the range of iron content in the alloy where the pressure resistance improvement effect can be obtained by adding calcium is as follows.
It is limited to a range of more than 0.4% and less than 0.8%. This is because if the iron content is less than 0.4%, there is no problem with the pressure resistance of the alloy casting, and if the iron content exceeds 0.8%, even the addition of calcium will not have a sufficient effect of improving the pressure resistance. The alloy of the present invention is produced by the general method normally used for this type of alloy system, and calcium is added by metallic calcium or aluminum.
A calcium mother alloy or a calcium-containing flux is used. In addition, when producing various cast products by casting the alloy of the present invention, treatment for improving the casting structure using sodium or strontium, etc., and refinement treatment for the casting structure using titanium, boron, etc., are carried out extensively in this type of alloy system. The inclusion of these metals added to the alloy by the above methods does not impede the effects of the present invention, so long as these treatments are carried out within the range of conventional methods. The alloy of the present invention can of course be applied to sand mold casting and die casting, but it can also improve the pressure resistance of cast products when applied to die casting and low pressure casting, which are becoming larger in size in recent years. Next, examples of the present invention will be shown. (Example) Alloys with various compositions as shown in Table 1 were melted and cast into JIS boat bottom molds and tater molds at a casting temperature of 720°C and a mold temperature of 200°C. A test piece for observation of nesting was created. Note that calcium in the alloy composition was added using an aluminum-5% calcium mother alloy. To measure strength and elongation, test specimens are held at 500°C for 6 hours, water quenched, and then tempered at 180°C for ₆ hours.
This was done after the treatment. To observe shrinkage cavities, the alloy casting cast in the Tater mold is divided into two in the vertical direction, the divided surfaces are faceted and smoothed, and then a color check is performed.
We investigated the presence of nests. These results are the first
Shown in the table. For the observation results of shrinkage cavities, refer to the experimental results shown in Figure 1, and those with no harmful shrinkage cavities observed in a are ranked A and b, c, and d.
They were ranked as B, C, and D according to the degree of conspicuousness of the shrinkage cavity.

[Table] *: ppm display From the results in Table 1, conventional aluminum-silicon-magnesium alloys without calcium addition (sample numbers 1 to 4) and aluminum-silicon-magnesium-copper alloys (sample numbers 9 to 11) As long as the iron content in the alloy is low, the shrinkage cavity rank is A and there is no problem (sample number 1), but when the iron content exceeds 0.2% (sample numbers 2 to 4 and 9).
~11) Harmful shrinkage cavities have been observed, and as the content increases, the amount of these harmful shrinkage cavities increases in B, C, and D, causing problems with the pressure resistance of castings made with these alloys. However, in the first to fourth alloys of the present invention (sample numbers 5 to 8 and 12 to 15) in which calcium is added to these alloy systems within the scope of the present invention, the iron content in the alloys is amount is 0.2
%, no harmful shrinkage cavities are present at rank A, indicating that the alloys of the present invention have excellent pressure resistance. In addition, the strength and elongation measurement results show that the aluminum-silicon-magnesium alloy and the aluminum-silicon-magnesium-copper alloy of the present invention have generally higher strength and elongation than conventional alloys containing silicon, magnesium, and copper with the same composition. It can be seen that the mechanical properties, especially the toughness, are improved. (Effects) As mentioned above, conventional aluminum-silicon-magnesium alloys or aluminum-
The aluminum alloy for casting of the present invention, which is a silicon-magnesium-copper alloy containing an appropriate amount of calcium, has a high iron content in the alloy. Since there are no defects caused by internal shrinkage cavities of a special shape caused by the formation of iron compounds, it has excellent pressure resistance.
It also has improved strength and toughness, making it ideal for casting engine parts such as pistons for automobiles and ships, hydraulic containers, and other machine parts that require pressure resistance. In addition, when mixing scrap materials and secondary alloy ingots in foundries, etc., it is extremely efficient and economical because the alloy can be melted without having to worry about adjusting iron impurities in the mixed ingots. .

[Brief explanation of the drawing]

Figures 1a, b, c, and d are specimens for observation of shrinkage cavities using a color check to show the relationship between the iron content in the alloy and the state of occurrence of shrinkage cavities in conventional aluminum-silicon-magnesium-copper alloys.
This sample also serves as a ranking sample that indicates the degree of shrinkage cavity generation means, and indicates that the amount of shrinkage cavities increases in the order of A, B, C, and D.

Claims (1)

[Claims] 1. Silicon 4-11%, magnesium 0.1% by weight
-2%, calcium 0.001-0.01%, the balance consists of aluminum and impurities, and the content of iron in the impurities is more than 0.4% and less than 0.8%, and has excellent pressure resistance for casting. 2 By weight, silicon 4-11%, magnesium 0.1
~2%, copper less than 5%, calcium 0.001~0.01%
An aluminum alloy for casting with excellent pressure resistance, the balance being aluminum and impurities, with an iron content of more than 0.4% and less than 0.8%. 3 By weight, silicon 4-11%, magnesium 0.1
~2%, calcium 0.001~0.01%, and one or more of 1% or less manganese and 3% or less nickel, with the balance consisting of aluminum and impurities, and the iron content in the impurities is
An aluminum alloy for castings with excellent pressure resistance of more than 0.4% and less than 0.8%. 4 By weight, silicon 4-11%, magnesium 0.1
~2%, copper less than 5%, calcium 0.001~0.01%
and further contains one or more of manganese or less and nickel or less and 3% or less, with the balance consisting of aluminum and impurities, and the iron content of the impurities is more than 0.4% and less than 0.8%. Aluminum alloy for casting with excellent properties.