JPH0368098B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field This invention is an Al-Mg alloy hot-rolled sheet that is used as hot-rolled for various large welded structural materials, etc., and in particular, the Mg content is increased to 5.7% or more to increase the strength. This relates to a hot-rolled Al-Mg alloy sheet. Note that in this specification, a hot-rolled plate means a plate that has been finished by a hot rolling mill and is not passed through a cold rolling mill. Prior art The 5083 alloy, which is a typical conventional Al-Mg alloy, is
As it is a non-heat-treated high-strength material, with recent advances in welding technology, it has become suitable for large welded structures such as onshore LNG (liquefied natural gas) storage tanks, tanker tanks, and large forming welds such as tank trucks. Although they are now widely used in structures, there is a strong desire to further improve the strength of this type of alloy and reduce its thickness in order to reduce costs by reducing the amount of material used. Furthermore, this type of Al-Mg alloy is expected to be applied to high-strength structural materials with low electrical conductivity, such as vacuum chamber materials for experimental fusion reactors and other auxiliary equipment, and for this purpose, further efforts are needed. High strength is desired. On the other hand, heat-treated alloys have traditionally been used as molds for plastic molding, but
Heat-treated alloys generally have high internal stress, which often causes problems in terms of dimensional accuracy after cutting. Therefore, Al-, which is a non-heat-treatable alloy with low internal stress,
By increasing the strength of the Mg alloy, Al-Mg is suitable for use in this type of plastic molding mold.
Demand for base alloys is also expected. By the way, 5083 alloy is Mg4.0 according to the JIS standard.
~4.9%, Mn0.30~1.0%, Cr0.05~0.25%, with the balance consisting of Al and inevitable impurities, and other impurity components include Cu0.10% or less and Si0.40% or less. , Fe 0.40% or less, Zn 0.25% or less, and Ti 0.15% or less are allowed. The alloying elements that contribute to the strength of 5083 alloy are mainly Mg, Mn, and Cr. Among these, Mg has a particularly high content, so Mg
has the highest contribution to the strength. Therefore, Al−Mg
In order to increase the strength of the alloy compared to the conventional 5083 alloy, it is possible to increase the amount of Mg added to 5% or more compared to the case of 5083 alloy, and it is actually possible to increase the strength by increasing the amount of Mg. However, on the other hand, if the amount of Mg is increased, a problem arises in that hot rollability is significantly impaired, as will be described in detail below. Therefore, in the past, Al-Mg based alloys
The amount of Mg was normally 4.9% or less as specified in the 5083 alloy. Problems to be solved by the invention As mentioned above, increasing the amount of Mg in Al-Mg alloys is effective in improving strength, but on the other hand,
If the amount of Mg is increased, hot deformation resistance will increase due to the solid solution hardening mechanism of Mg, and hot rollability will be significantly impaired. Furthermore, if the Mg content increases beyond around 6%, low melting point eutectics such as β phase (Al ₃ Mg) will be present at grain boundaries, promoting intergranular cracking during hot deformation. Edge cracking (edge cracks) during hot rolling
Alligator cracks (crocodile cracks) are more likely to occur. In particular, in this type of alloy, the presence of even a trace amount of Na or Ca significantly increases the susceptibility to brittle cracking during hot rolling. Increasing the amount of Mg in the Al-Mg alloy compared to the amount of Mg in the conventional typical 5083 alloy (4.0 to 4.9%) is effective in improving strength, but it significantly impairs hot rollability. 5% or more due to deterioration.
The reality is that it has been difficult to produce Al-Mg-based alloy plates containing Mg on an industrial scale, even on a laboratory scale. Methods to improve the hot rolling properties of Al-Mg alloys include minimizing trace amounts of harmful impurities such as Ca and Na, as well as segregation of alloy components at grain boundaries and low melting point eutectic impurities. It is thought that it is necessary to remove the inclusions by sufficient soaking treatment, but with the former method alone, Al containing a large amount of Mg
- It is difficult to significantly improve the hot rolling properties of Mg alloys, and on the other hand, even in the latter method, it is difficult to soak to the point where low melting point eutectic inclusions are sufficiently removed on a commercial scale. In systems containing Mg at a high concentration of 5 to 6% or more, it is difficult to improve hot rolling properties by soaking alone. This invention was made against the background of the above-mentioned circumstances, and in order to improve the strength, 5.7% or more
The object of the present invention is to provide a hot-rolled sheet of an Al-Mg-based alloy that has sufficiently improved hot rolling properties in a high-Mg-based Al-Mg alloy to which Mg has been added. Means for Solving the Problems The present inventors have investigated the following means as a measure to improve the hot rolling properties of high Mg Al-Mg alloys. In other words, since fractures during hot deformation are mainly grain boundary fractures, we investigated ways to alleviate the concentration of deformation strain at grain boundaries. in this way
As a result of repeated research to find specific measures to alleviate the concentration of deformation strain at grain boundaries during hot deformation of Al-Mg alloys, we found that by actively adding Fe, Al as a second phase compound −Dispersing the Fe eutectic compound and further dispersing the eutectic compound with Mn
As an Al-Fe-Mn-based compound that is stable at high temperatures in the coexistence of , actually alleviates the concentration of deformation strain on the grain boundaries, resulting in high
It was discovered that even Mg-based Al-Mg alloys can significantly improve hot rolling properties, leading to the present invention. Specifically, the Al-Mg alloy hot-rolled sheet of the first invention contains 5.7 to 9% Mg, 0.05 to 1.0% Mn, and 0.05 to Cr.
0.3%, Ti 0.005-0.2%, Fe 0.25-1.00%, and the remainder consists of Al and inevitable impurities. Moreover, the Al-Mg alloy hot-rolled sheet of the second invention further contains 0.05 to 0.3% of Cu in addition to the above-mentioned components. Effect In a high Mg Al-Mg alloy with an Mg content of 5.7 to 9%, by adding Fe, an Al-Fe eutectic compound is dispersed and crystallized as a second phase compound. Since this eutectic compound is dispersed and crystallized near the grain boundaries during the solidification process, the strain of hot deformation is also shared from the grain boundaries to these dispersed and crystallized compounds. Also, Al crystallized during the solidification process.
- Fe-based eutectic compounds are Al-Fe-Mn that is stable at high temperatures during various thermal history processes after casting due to the coexistence of Mn.
The Al-Fe-Mn-based compound is further uniformly broken and dispersed during the hot rolling process, and as a result, the hot deformation strain is evenly distributed,
It plays a role in improving hot rolling properties. Further, by adding Ti (combined addition of Ti and B if necessary), crystal grains are made finer. By refining the crystal grains in this way, the alloying elements segregated to the grain boundaries can be easily diffused and homogenized by soaking treatment, and the low melting point eutectic such as the β phase described above can be refined and dispersed. This is achieved, and the degree of concentration of strain deformation on individual grain boundaries is also reduced, which together act to improve hot rollability. In this way, the crystallization of the second phase compound due to the addition of Fe and the grain refinement due to the addition of Ti (combined addition of Ti + B as necessary) combine to achieve high
Even Mg-based Al-Mg alloys can sufficiently improve hot rolling properties. Reasons for Limiting Components Next, the reasons for limiting each component in this invention will be explained. Mg: Mg is an effective element for increasing the strength of non-heat-treated Al alloys, but if the amount is less than 5.7%, the high strength targeted by this invention cannot be achieved.
Furthermore, when the Mg content is less than 5.7%, hot rolling properties do not pose much of a problem. On the other hand, even if Mg is increased beyond 9%, the contribution to strength improvement will be small and it will be uneconomical, so it is limited to a range of 5.7 to 9%. In order to obtain particularly high strength within this range, Mg
It is desirable that the amount is 6% or more, more preferably 7% or more. Mn, Cr: These elements are effective in ensuring strength, especially proof stress, and reducing stress corrosion cracking, but each
These effects cannot be obtained at less than 0.05%. on the other hand
If Mn exceeds 1.0% and Cr exceeds 0.3%, intermetallic compounds will increase, and sometimes large intermetallic compounds will crystallize, making it impossible to obtain a healthy ingot and potentially impairing the uniformity of the quality of the rolled material. From, Mn is 0.05-1.0%, Cr is
It was limited to within the range of 0.05-0.3%. Ti: Ti is an element that is effective in refining crystal grains.
Ti plays a role in improving hot rollability through grain refinement, but if it is less than 0.005%, the effect of grain refinement is not recognized, while if it exceeds 0.2%, the toughness will deteriorate, so the amount of Ti added is It was limited to within the range of 0.005-0.2%. Note that when Ti is added in combination with B, it exhibits a more pronounced crystal grain refining effect than when Ti is added alone, so it can be added as necessary.
B may be added together with Ti. However, B is 0.001
If it is less than 0.1%, the effect will be small, whereas if it exceeds 0.1%, the toughness will deteriorate. Therefore, when B is added in combination with Ti, it is preferable that the amount of B is within the range of 0.001 to 0.1%. Fe: As mentioned above, Fe crystallizes an Al-Fe-based eutectic compound during the casting stage. Due to the coexistence of Mn, this Al-Fe-based eutectic compound becomes an Al-Fe-Mn-based compound that is stable at high temperatures during various thermal history processes after casting, and is uniformly broken and dispersed during the hot rolling process.
It plays a role in promoting the dispersion of deformation strain during hot deformation and improving hot rollability. When Fe is less than 0.25%, Al− containing Mg at a high concentration of 5.7% or more
It is difficult to sufficiently improve the hot rolling properties of Mg alloys, and on the other hand, if Fe exceeds 1.00%, the number of compounds distributed is too large, which may deteriorate the ductility and toughness of the alloy material. Therefore, Fe is 0.25-1.00%
was within the range of In addition to the above-mentioned component elements, in the second invention of the present application,
It is assumed that Cu is contained in an amount of 0.05 to 0.30%. In other words, Cu is effective in improving stress corrosion cracking resistance, but this effect is not observed at less than 0.05%;
If it exceeds 0.30%, Al− containing a high concentration of Mg
Since there is a risk of impairing hot rolling properties in Mg alloys, the Cu content in the second invention was set to 0.05 to 0.30%. Furthermore, in the alloy of this invention, Si is an unavoidable impurity, and Zn is another impurity.
may be included, and these are permissible within the following ranges: That is, Zn is allowed up to 0.50%. Zn
If it exceeds 0.50%, problems will arise especially in the corrosion resistance of the weld heat affected zone. Furthermore, Si is allowed up to 0.40%.
If Si exceeds 0.40%, Al-Mg-Si-based eutectic compounds increase, and these tend to melt during welding with large heat input, leading to micro-cracks at grain boundaries in the heat-affected zone. The alloy of this invention is an alloy containing a high concentration of Mg, which is easily oxidized. Therefore, in order to prevent oxidation of the molten metal during melting and casting of the alloy, the Be content is set at 0.0001 to 0.0001.
It is preferable to add about 0.002%. Example Alloys with the compositions shown in No. 1 to No. 12 in Table 1 were
Add 1 to 2 ppm of Be and melt it, and the thickness is determined by the mold.
It was cast into an ingot measuring 40 mm, width 110 mm, and height 150 mm. The ingot was then subjected to soaking treatment at 460° C. for 30 hours or more, and then faceted by 1 mm on both sides in the thickness and width directions to a thickness of 38 mm, width of 108 mm, and height of 150 mm. The ingot after face cutting is heated to 460℃.
After heating for 1 hour in an experimental rolling mill, the roll was rolled at 460° C. and reloaded in a furnace at a rolling reduction of 2 mm per pass, and hot rolled from 38 mm to 5 mm thick. Then, hot rolling properties were evaluated by observing the presence or absence of alligator cracks during hot rolling and ranking the occurrence of cracking at the edge after rolling to a thickness of 5 mm. Further, each plate of the hot rolling mill was subjected to finish annealing at 350°C for 50 hours to obtain a zero material, and then a tensile test was conducted to examine the mechanical properties. The results are shown in Table 2. In addition, in Table 2, ranks A, B, and C of the occurrence of edge cracking regarding the evaluation of hot rollability were classified as follows. In other words, A is when the occurrence of edge cracks remains as small as the conventional 5083 alloy.
B indicates a case where edge cracking exceeds that of conventional 5083 alloy and is 10 mm or less, and C indicates a case where edge cracking of 10 mm or more occurs. As is clear from Table 2, all of the alloys within the composition range of this invention (No. 1 to No. 5) exhibited good hot rollability equivalent to that of the conventional 5083 alloy, and their strength was also improved, especially since they contained Mg. Alloys No. 1, 3 to 5 with a content of 7% or more have a tensile strength of 37Kg/mm3 ^or more and a yield strength of 17Kg/mm3.
It was confirmed that it exhibits high strength and yield strength with a value of mm ³ or more. On the other hand, comparative alloys Nos. 9, 10, and 12 with Fe contents lower than the range of the present invention, and comparative alloy No. 11 without Ti addition, all have poor hot rollability, and also have Cr or Mn. It was found that Comparative Alloys No. 7 and 8, in which the content was lower than the range of the present invention, had poor yield strength.

【table】

[Table] Effects of the invention As is clear from the above explanation, the Al-
Although the Mg alloy hot-rolled sheet has an increased amount of Mg compared to the conventional 5083 alloy to improve strength, its hot rolling properties are lower than that of the conventional 5083 alloy.
It is as good as or better than 5083 alloy, and can be stably made into crack-free plates without hindrance to hot rolling. Therefore, non-heat treated high strength
It has become possible to manufacture Al-Mg alloy materials with even higher strength than conventional sheets on a commercial scale as Al alloy hot-rolled sheets, and by thinning large welded structures using Al-Mg alloys, It is possible to reduce the cost of the structure, and by applying it to fields where heat treatable alloys have been used in the past, it is possible to bring about various benefits such as being able to reduce heat treatment costs.

Claims (1)

[Claims] 1 Mg5.7-9%, Mn0.05-1.0%, Cr0.05-0.3
%, Ti0.005~0.2%, Fe0.25~1.00%,
A hot-rolled aluminum-magnesium alloy hot-rolled sheet with excellent hot rollability, characterized in that the remainder consists of Al and unavoidable impurities. 2 Mg5.7~9%, Mn0.05~1.0%, Cr0.05~0.3
%, Ti0.005~0.2%, Fe0.25~1.00%, Cu0.05~
A hot-rolled aluminum-magnesium alloy hot-rolled sheet with excellent hot rollability, characterized in that the aluminum-magnesium alloy contains 0.3% and the remainder consists of Al and unavoidable impurities.