JPH0355537B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field This invention relates to aluminum alloys, particularly Al-Zn-Mg or Al-
This invention relates to a Zn-Mg-Cu-based aluminum alloy with high strength, excellent formability, and improved stress corrosion cracking resistance. In this specification, all "%" used for alloy components are based on weight. Conventional technology and problems Among 7000 series alloys, that is, Al-Zn-Mg alloys, 7003 alloy is a typical structural alloy that has relatively high strength and can be extruded. known. In addition, it is a representative alloy that has the highest strength among various aluminum alloys including 7000 series alloys and can be rolled.
7075 alloy is well known. However, even with the above-mentioned 7003 alloy, it was not always possible to obtain sufficiently satisfactory excellent extrudability.
The 7075 alloy could not necessarily be said to have satisfactory rolling properties. Furthermore, in recent years, in the use of various structural materials,
There is a strong demand for thinner and lighter materials, and there is a strong demand for increasing alloy strength. Under these circumstances, while maintaining good extrudability, rollability, and especially hot formability,
In order to further increase the strength, attempts have been made in the prior art to increase the Zn content or further increase the Mg content. However, when the Zn content is increased, the alloy becomes more susceptible to stress corrosion cracking, and there is a tendency for the alloy to become unusable in applications such as structural materials. Furthermore, when the Mg content is increased, the moldability decreases, particularly hot formability such as rollability and extrudability, or even cold formability, which tends to result in poor productivity. Furthermore, in the case of 7075 alloy, it is highly susceptible to stress corrosion cracking, so conventionally heat treatment was performed under conditions that would give the alloy its maximum strength.
The reality is that it is put into practical use in a tempered state equivalent to that of _T7 material, whose structure has been stabilized by tempering at a higher temperature and for a longer time than _T6 treatment. For this reason, there was a problem in that the strength had to be sacrificed by 10 to 20% compared to _T6 material, which provides the highest strength. Due to the above-mentioned circumstances, the conventional technology provides sufficient satisfaction in both strength and stress corrosion cracking resistance.
Furthermore, it has been extremely difficult to obtain aluminum alloys that have excellent formability such as extrudability and rollability. Based on the background of the prior art as described above, the present invention is based on the 7000 series Al-Zn-Mg series or Al-Zn
An object of the present invention is to provide an aluminum alloy based on a -Mg-Cu alloy that has the beneficial properties inherent therein and has improved formability and stress corrosion cracking resistance. Means for Solving the Problems Based on the above objectives, the inventors conducted various experiments and research and found that Al-Zn-, which has been widely used as a high-strength wrought material, Based on Mg-based alloys, by keeping the Mg content relatively low and adding rare earth elements such as Y, La, Ce, Pr, Nd, and Sm, the inherent excellent mechanical properties of the above alloys are enhanced. In addition to improving extrudability during the production of alloys, hot rolling properties for obtaining plate materials, and furthermore cold workability, Al-Zn-Mg based It has been found that the low stress corrosion resistance, which is a common drawback of alloys, can be significantly improved. Therefore, this invention was completed based on the above findings, and one of the invented alloys is:
As essential elements, Zn is 3-12% and Mg is more than 1.5%.
Contains less than 2.5% of Cu, or further contains Cu.
0.05-3.0%, and (or) Mn: 0.1-1.0%,
Contains one or more of Cr: 0.05-0.3%, Zr: 0.05-0.25%, and further contains rare earth elements such as Y, La, Ce, Pr, Nd, and Sm as main essential elements. The gist is an aluminum alloy containing one or more selected from the group in a total amount in the range of 0.5 to 10%, with the remainder consisting essentially of Al and inevitable impurities. The above-mentioned alloy according to the present invention retains the inherently excellent mechanical properties of Al-Zn-Mg alloys by containing Zn and Mg, while improving workability and improving workability by containing rare earth elements. In particular, it improves hot workability, significantly reduces stress corrosion cracking susceptibility, and exhibits excellent durability even under practical conditions under load stress. Also,
The addition of Cu further increases the strength of the alloy. Furthermore, the alloy of the present invention further contains one or more elements selected from the group of Mn, Cr, and Zr in the above range, so that the alloy contains a Refine the crystal grains and make the structure even more stable. Next, the significance of each chemical component of the aluminum alloy and the reason for limiting its content range will be explained as follows. As is well known, Zn contributes to improving the strength of aluminum alloys. Zn content is 3
If it is less than %, the required high strength cannot be obtained from the alloy. However, even if it is contained in a large amount exceeding 12%, the strength will not be improved comparatively, and the content of more than that is essentially meaningless. Therefore, the effective content of Zn is in the range of 3 to 12%, but when it is desired to obtain particularly high strength, Zn can be added in a relatively large amount, that is, in the range of 7.0 to 10.0%. It is effective to add and contain it within the range. Mg also contributes to improving the strength of aluminum alloys. Therefore, in order to obtain good high strength equivalent to 7000 series alloys, it is necessary to contain at least 1.5%. However, as the Mg content increases, the ductility of the alloy decreases and the workability decreases. Although it is possible to increase the Mg content to about 5.0% in order to obtain as high strength as possible even at the cost of some degree of workability, it is possible to increase the Mg content to about 5.0%. For the purpose of obtaining extrudability, rollability, and other processability, the Mg content is 2.5%.
The limit is less than That is, when Mg is contained in an amount of 2.5% or more, the ductility decreases, making it impossible to obtain fully satisfactory results in terms of rolling properties, extrudability, and other processability. The rare earth elements that are the most important additive elements in this invention are 15 elements with atomic numbers from 57 to 71, i.e.
La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb,
It consists of a group of 17 elements including Dy, Ho, Er, Tm, Yb, Lu, and these plus Y and Sc. These elements do not necessarily need to be used as individual elements, and Mitsushi metal obtained by electrolyzing mixed chlorides of rare earth metals may be used. Industrially, Y, La, Ce, Pr, Nd, Sm are used due to their ease of acquisition.
It is preferable to use one type or a combination of two or more types selected from the group below. This rare earth element is contained in the aluminum alloy of the present invention and has the effect of mainly improving the formability of the alloy and improving the stress corrosion cracking resistance. In view of this effect, all of the rare earth elements in the above groups can be evaluated as substantially equivalent to each other in the present invention. Therefore, one or more of them can be used in any combination, but if the total content in the alloy is less than 0.5%, it is insufficient to improve the formability and stress corrosion cracking resistance. On the other hand, if the content exceeds 10%, the stress corrosion cracking resistance will not improve much, but rather a large number of coarse crystallized substances will be generated in the alloy, increasing the possibility that the strength will decrease. Therefore, the permissible content of rare earth elements is 0.5-10
%, but in order to provide the generally desired high stress corrosion cracking resistance, a relatively high content within the above range should be selected, taking into account the relationship with cost. , preferably in the range of 2.0 to 7.0%, and most preferably in the range of 4.0 to 6.0%, great satisfaction can be obtained. In addition to the effect of increasing stress corrosion cracking resistance, the inclusion of rare earth elements also makes the crystal structure in the alloy fine and stable as described above, resulting in improved formability in extrusion, rolling, etc. However, it shows a remarkable effect. Therefore, with the application of this invention, it is possible to efficiently industrially produce alloys that are extremely difficult to extrude or roll even if high strength can be expected from their composition using conventional techniques. .
For example, a high-strength alloy containing a large amount of Zn, a reinforcing element, exceeding 7.0% can be easily produced without any problems. As is known, Cu contributes to improving strength, but if the content is less than 0.05%, the effect is not sufficient, and even if it is more than 3.0%, it has no effect on improving strength. This is not preferable because it increases the susceptibility to weld solidification cracking, worsens weldability, and reduces corrosion resistance and hardenability. Therefore, even within the content range specified above, if particularly high strength is required, it may be added close to the upper limit, but for alloys used for welded structural materials. In such cases, it is desirable not to actively include Cu beyond the content range as an impurity, or to include it within a relatively low range of 0.3% or less. Mn, Cr, added in the alloy of this invention
Zr is useful for refining crystal grains during hot working, but if Mn is less than 0.1, Cr is less than 0.05%, and Zr is less than 0.05%, the above effects will be poor.
When Mn: exceeds 1.0%, Cr: exceeds 0.3%, and Zr: exceeds 0.25%, coarse crystallized substances are generated in the alloy, reducing the strength of the alloy. Effects of the Invention As will be understood from the Examples described later, the aluminum alloy according to the present invention is an Al-Zn-Mg alloy, and although it has high strength inherent to it, it is different from conventional alloys. It has superior workability such as extrudability and rollability, and is also significantly superior in stress corrosion cracking resistance. Therefore, in various applications where the alloy is used as a wrought material such as extruded material, rolled material, forged material, etc., it is possible to make it thinner and lighter while improving its formability even more than conventional alloys. In particular, even if the alloy corresponds to the conventional 7075 alloy in terms of Mg and Cu contents, the improved alloy further containing rare earth elements according to the present invention can have the highest strength. It becomes possible to put it into practical use as a _T6 heat treated material. In addition, it has the advantage of being able to further increase productivity compared to conventional alloys due to improved workability such as extrudability and rollability. Examples Example 1 Aluminum alloys of various compositions Nos. 1 to 14 shown in Table 1 below were cast into billets with a diameter of 3 inches using a water-cooled mold. Next, this billet was homogenized at 460°C for 12 hours, then loaded into an extruder container and heated to 450°C.
It was extruded at ℃ into a flat bar with a cross-sectional size of 3 mm x 30 mm.

【table】

[Table] The extrudability of each alloy was also evaluated at the above-mentioned limit extrusion speed during extrusion processing. In addition, each of the above extruded materials was solution-treated by heating at a temperature of 460°C for 2 hours, then water-cooled and quenched, and further
Manufactured into _T6 material by artificial aging treatment at 120℃ for 24 hours. Using each T ₆ obtained by this as a sample,
Their stress corrosion cracking resistance and tensile strength as one of the mechanical properties were investigated. those results as a second
Shown in the table. Note that the alloy numbers in Table 2 are the same as the alloy numbers in Table 1. The numerical value shown as the evaluation of extrudability represents a relative evaluation value when compared to A6063 aluminum alloy, which is known as a typical extrusion alloy, and assuming that the limit extrusion speed of the 6063 alloy is 100. . In addition, the stress corrosion cracking resistance test results are as follows: 20 kg in the rolling or extrusion direction of the test piece in a 3.5% NaCl aqueous solution.
The graph shows the number of days until cracking occurs when a stress of f/mm ² is applied.

【table】

[Table] As seen in the results in Table 2 above, the alloy according to the present invention falls within the range of aluminum alloys containing a high percentage of Zn and a relatively low Mg content. Although it possesses high strength as an inherent property, it has excellent extrudability that is equivalent to or better than comparative alloys that do not contain rare earth elements, and it has significantly superior stress corrosion cracking resistance. It can be seen that it has properties. Moreover, the alloy according to the present invention has finer grains than comparative alloys, and has improved hardenability and
It also had excellent weldability. Example 2 Alloy Nos. 1 to 5, 7 to 9 and No. shown in Table 1 above.
10 types of alloys 15 and 16 were cast in a water-cooled mold to a size of 50 mm thick and 150 mm wide. This was then hot rolled at 450°C to a thickness of 3 mm. Then, the rollability was evaluated based on the required number of passes of hot rolling from 50 mm to 3 mm in thickness, and the results are shown in Table 3. The alloy numbers in the same table correspond to the numbers in Table 1. In addition, for each rolled plate obtained as above,
After applying heat treatment as in Example 1 to obtain T ₆ materials, these were used as test materials to examine stress corrosion cracking life and tensile strength in the same manner as in Example 1 above. The results are shown in Table 3.

【table】

[Table] As can be easily understood from the results shown in Table 3, the aluminum alloy according to the present invention has a high strength comparable to that of the comparative alloy even when manufactured into a rolled material. It had excellent stress corrosion cracking resistance and even better rolling properties.

Claims (1)

[Claims] 1. High strength containing 1 Zn: 3 to 12%, Mg: more than 1.5% and less than 2.5%, one or more rare earth elements: 0.5 to 10%, and the balance is Al and inevitable impurities. Aluminum alloy. 2 Zn: 3-12% Mg: More than 1.5% but less than 2.5% Cu: 0.05-3.0% One or more rare earth elements: 0.5-10% High strength consisting of Al and inevitable impurities. Aluminum alloy. 3 Zn: 3-12% Mg: More than 1.5% and less than 2.5% Contains one or more rare earth elements: 0.5-10%, and Mn: 0.1-1.0% Cr: 0.05-0.3% Zr: Contains one or more of 0.05 to 0.25%, with the remainder being Al.
A high-strength aluminum alloy consisting of and unavoidable impurities. 4 Contains Zn: 3-12% Mg: More than 1.5% and less than 2.5% Cu: 0.05-3.0% One or more rare earth elements: 0.5-10%, and Mn: 0.1-1.0% Cr: Contains one or more of the following: 0.05-0.3% Zr: 0.05-0.25%, the remainder being Al
A high-strength aluminum alloy consisting of and unavoidable impurities.