JPH0441649A - Aluminum alloy excellent in scc resistance and having high strength and high formability - Google Patents

Abstract

PURPOSE:To obtain a clad plate of Al alloy excellent in stress corrosion cracking resistance by optimizing a composition containing Mg and Cu as to core material and also optimizing a composition containing Mg and Si as to cladding material. CONSTITUTION:An aluminum alloy which has a composition consisting of 4-10% Mg, 0.2-1.0% Cu, <=0.2% Fe, <=0.2% Si, and the balance Al with impurities or an aluminum alloy which has a composition further containing, besides the above, one or >=2 kinds among 0.01-0.2% Cr, 0.01-0.2% Zr, and 0.02-0.3% Mn is used as a core material and an aluminum alloy which has a composition consisting of 0.4-1.5% Mg, 0.3-2.0% Si, and the balance Al with impurities is used as a cladding material, and further, the thickness of the cladding material is regulated to 2-20% of the whole plate thickness per side, by which the aluminum alloy excellent in SCC resistance and having high strength and high formability can be produced.

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to a high-strength, high-formability aluminum alloy with excellent SCC resistance (stress corrosion cracking resistance).
The present invention relates to an aluminum alloy that is suitable for products that are subjected to electrodeposition coating after press working, has excellent moldability, and has improved SCC resistance and string rust resistance after electrodeposition coating. (Conventional technology and problems to be solved) Traditionally, such as automobile body panels and reinforcement parts,
AQ-Mg alloy containing 2 to 5% Mg (
For example, soft materials such as 5052.5154.5182) have been put into practical use. However, although these aluminum alloys have good moldability, they cannot cope with the increasingly complex shapes of molded products these days, and they have the problem of cracking when the molding conditions are severe. For this reason, research has been conducted to improve workability by increasing the amount of Mg in AQ-Mg alloys, but if the amount of Mg exceeds 3.5%, high temperature There were problems in that 5CC (stress corrosion cracking) was likely to occur during use in an atmosphere, and thread rust resistance after paint baking was likely to be poor. In order to solve this problem, the applicant first added Zn: 0 to an aluminum alloy core material containing Mg: 3 to 10% in order to improve formability and SCC resistance. We proposed an [aluminum alloy composite plate with excellent formability and stress corrosion cracking resistance] clad with aluminum alloy skin material containing 5 to 17% (Special Publication No. 62-1626).
No. 3). Further, it contains Mg: 3 to 10%, or Mg: 3 to 10%.
The core material is an aluminum alloy containing one or two of Zn: 2% or less and Cu: 2% or less, and is clad with pure AΩ. Tokuko Sho 63-209, which proposed “aluminum alloy plate”
No. 05). Furthermore, Japanese Patent Application Laid-Open No. 1983-1999 proposed an "aluminum alloy plate with excellent formability and thread rust resistance" which was clad with an aluminum alloy containing 0.5 to 4.0% Mn as a skin material.
1-91343). However, in all aluminum alloys, there is a decrease in strength due to the composite effect and a change in strength due to aging due to the addition of Zn, so it cannot be said that they are necessarily satisfactory. The present invention solves the above-mentioned drawbacks of the prior art, and provides an aluminum alloy that has high strength after baking, excellent moldability, excellent SCC resistance, and can improve string rust resistance after electrodeposition coating. The purpose is to provide (Means for Solving the Problems) In order to achieve the above object, the present inventor has developed an aluminum alloy that can improve SCC resistance while ensuring moldability, and further improve thread rust resistance after baking coating. As a result of our efforts to develop the core material, we discovered that it is possible to achieve this by optimizing the component composition containing Mg and Cu, and for the skin material by optimizing the component composition containing Mg and Si. The present invention has been made in this way. That is, in the present invention, Mg: 4 to 10% and Cu: 0.
Contains 2 to 1.0%, Fe: 0.2% or less, Sj20
．． Controlled to 2% or less, with the remainder made of AQ and impurities as the core material, or further Cr: 0.01
-0.2%, Zr: 0.01-0.2% and Mn: 0.
The core material is an aluminum alloy containing one or more of 02 to 0.3%, Mg: 0.4 to 1.5% and Si: 0.3 to 2.0%, High strength and high formability with excellent SCC resistance, characterized in that the skin material is an aluminum alloy with the remainder consisting of AQ and impurities, and the thickness of the skin material is 2 to 20% of the total plate thickness on one side. The focus is on aluminum alloys. The present invention will be explained in more detail below. (Function) First, the reason for limiting the chemical components of the core material and the skin material will be explained. ■ L waste material Mg: Mg is an element that reduces string rust resistance and SCC resistance, and improves moldability and strength. It is effective in improving elongation. However, if it is less than 4%, moldability deteriorates and strength decreases. On the other hand, if it exceeds 10%, Mg becomes oxidized during melting and cracks easily during casting, and rollability decreases due to increased processing resistance during hot rolling and cold rolling, which is not preferable. Therefore, the Mg content is in the range of 4 to 10%. Cu: Cu is an element that imparts strength and SCC resistance, and has a great effect of improving strength, especially after baking coating. On the other hand, regarding SCC resistance, P only exists in a solid solution state.
It is effective because it suppresses phase precipitation. However, if the content is less than 0.2%, the effect will be low, and if the content exceeds 1.0%, the effects of improving strength and SCC resistance will begin to be saturated, and at the same time, rolling properties will decrease, which is not preferable. Therefore, the Cu content is in the range of 0.2 to 1.0%. Cr, Mn, Zr: Cr, Mn, and Zr are elements that improve moldability and strength, and are effective in improving SCC resistance, so at least one or more of them can be added in an appropriate amount as necessary. Can be added. However, Cr and Zr are each 0.01
%, Mn is less than 0.02%, there is no such effect, and Cr is 0.2%, Zr is 0.2%, Mn is 0.
If the content exceeds 3%, moldability becomes poor, which is not preferable. Therefore, the Cr content is between 0.01 and 0.01.
2%, Zr content is in the range of 0.01-0.2%, and Mn content is in the range of 0.02-0.3%. Fe, Si: Fe and Si are elements that impart moldability, but as their content increases, they produce coarse crystallized substances, which inhibits flat deformation during molding and reduces elongation. Especially each 0.
If the content exceeds 2%, moldability will deteriorate. Therefore, the Fe content is 0.2% or less, and the Si content is 0.2%.
% or less. In addition, in order to refine the crystal grains of the ingot, Ti or T is usually added.
i+B, in which case Ti:0.
If B is 1% or less and B: 0.02% or less, the effects of the present invention (molding processability, thread rust resistance, SCC resistance) will not be adversely affected. Furthermore, if impurities such as Zn and Ni are each 0.1% or less, they will not adversely affect the effects of the present invention (molding processability, SCC resistance). U skin material The skin material is required to have better thread rust resistance and SCC resistance than the core material, and also to have better moldability. Furthermore, it is desirable that the strength after baking the paint can be improved. Mg: Mg combines with Si to improve material strength and strength through baking, but if it is less than 0.4%, thread rust resistance, SCC resistance, and formability are good, but the strength after baking is low and If the content exceeds 1.5%, the strength of the material and the strength after baking will increase, but the moldability will decrease. Therefore, the Mg content is 0.4-1. The range shall be 5%. Sj: Si combines with Mg to increase the strength of the material and the strength after baking, and when added in excess of the composition ratio of Mg2Si, Si particles are dispersed to prevent uniform deformation during molding. It becomes easier to raise and improves moldability. However, if the content is less than 0.3%, the strength and strength after baking will be low, and if the content exceeds 2.0%, the strength of the material and the strength after baking will be high, but hot rolling properties and formability will decrease. do. Furthermore, the thread rust resistance after painting is also reduced. Therefore, the Si content is in the range of 0.3 to 2.0%. In addition, in order to impart strength and formability to the aluminum alloy having the above composition, Cu, Zn: 0.5
% or less, Fe, Mn, Cr, V, Zr: 0°2% or less,
One or two of Ti: 0.1% or less, B: 0.02% or less
More than one species may be included. In that case, if there are two or more types, it is best to limit it to 1% or less. It should be noted that if the content exceeds the upper limit, thread rust resistance and moldability will deteriorate. Next, the reason for regulating the thickness of the skin material relative to the core material will be explained. (3) Thickness of the skin material The skin material may be provided on either one or both sides of the core material, but the thickness of the skin material should be 2 to 20% of the total board thickness per side. is preferred. However, if it is less than 2%, the skin material will be damaged during manufacturing, and no improvement in thread rust resistance and SCC resistance will be observed, and even if the skin material is not damaged, the thickness of the skin material will be less than the total board thickness Since it is thin (less than 2%), it has little effect on improving SCC resistance and thread rust resistance, and when the thickness of the skin exceeds 20%, thread rust resistance and SCC resistance are not good. Although this is true, it is not preferable because it greatly reduces moldability. Therefore, the thickness of the skin material should be 2 to 20% of the total board thickness on one side, depending on SCC resistance, thread rust resistance, and moldability.
The range shall be . (Example) Next, an example of the present invention will be shown. As the core material and skin material, aluminum or aluminum alloy having the chemical composition shown in Table 1 is hot rolled (combined rolling The plate was then cold rolled to a thickness of 1.5 m, and then intermediate annealed at 350"C for 2 hours.Then the plate was rolled to a thickness of 1.0 mm (the skin thickness was 5% per side). Cold rolling was carried out until the core material was provided on both sides.This 1i++o thick aluminum alloy plate was
It was rapidly heated to 30°C, held at that temperature for 10 seconds, and then rapidly cooled at an average cooling rate of 600°C/win to obtain a test material. For each of the obtained test materials, the tensile strength of the material, the tensile strength after baking, and the Erichsen value (molding workability) were investigated, as well as the SCC resistance and the thread rust resistance after painting. The results are shown in Table 2. Note that the SCC resistance test method and thread rust resistance test method were carried out in the following manner. (1) SCC resistance test method A sample material with a thickness of 11 was cold rolled to a thickness of 0.7 mm,
After sensitization treatment at 120℃ x 7 days, 0.70+u
+t x 20mmw x 80mmQ cut, SC
C test was conducted. As for the SCC test conditions, the stress load uses the constant strain method using U-shaped bending, and the corrosive atmosphere is 3.5.
% NaCQ aqueous solution using an accelerated test method in which a current of 5 mA/1 nch2 was applied. SCC resistance is 0
(No cracking after 600 minutes or more), Δ (no cracking after 240 minutes or more), and X (cracking occurred after less than 240 minutes). (2) Thread rust resistance test method ■Preparation of test piece 70mm x 150mm test piece → Degreasing → Zinc phosphate treatment → Cationic electrodeposition coating (baking at 170°C for 30 minutes) → Intermediate coating (140°C for 30 minutes) → Top coating (140°C ℃ x 30 minutes) to prepare a test piece. ■ Corrosion test Artificially add a flaw (see Figure 1) marked with an
2371, 24 hr) → Wet test (240 hr at 80-85% temperature at 40° C.) Corrosion test was conducted. ■ Evaluation of thread rust resistance As shown in Figure 1, depending on the occurrence of thread rust from the artificial flaw (1), O (thread rust length less than 0.5 mm), O (thread rust length less than 0.5 mm),
It was evaluated as Δ (thread rust length: 0.5 m+a or more, less than 2 mm), × (thread rust length: 2 ffl11 or more). As can be seen from Table 2, it is clear that the examples of the present invention are superior in SCC resistance and thread rust resistance, as well as in strength and moldability, compared to the comparative examples. Disappointment 1 Regarding the combination of core material (C-1) or (C-4) and skin material (S-1) shown in Example 1, a plate thickness of 1.0 mm manufactured by the same method as Example 1 was used. A test material was prepared with skin material provided on both sides at 0 to 25% of the total board thickness on one side, and the thickness, tensile strength, formability, and durability of the skin material were determined by the same test as in Example 1. We investigated the relationship between SCC and sex. The results are shown in Table 3. As is clear from Table 3, SCC resistance is not improved when the skin thickness is less than 2% of the total plate thickness. Furthermore, when the thickness of the skin material exceeds 20%, although the SCC resistance is improved, the Erichsen value becomes low and the moldability becomes poor.

[Left below]

(Effects of the Invention) As detailed above, according to the present invention, not only SCC resistance but also good moldability, high strength, and excellent two-ply thread rust resistance are achieved. It is suitable for use in body panels, reinforcement parts, etc., and has great industrial effects.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating a test piece and test procedure for a thread rust resistance test. Patent applicant: Kobe Steel, Ltd. Patent attorney Nao Nakamura t4, @-&sa

Claims (2)

[Claims] (1) Contains Mg: 4-10% and Cu: 0.2-1.0% in weight% (the same applies hereinafter), Fe: 0.2% or less, Si: 0.2% or less The core material is an aluminum alloy with the remainder consisting of Al and impurities, and Mg: 0.4~
The skin material is an aluminum alloy containing 1.5% and Si: 0.3 to 2.0%, with the remainder consisting of Al and impurities,
A high-strength, highly formable aluminum alloy with excellent SCC resistance, characterized in that the thickness of the skin material is 2 to 20% of the total plate thickness on one side. (2) The core material further contains Cr: 0.01-0.2%, Z
r: 0.01-0.2% and Mn: 0.02-0.3%
The high-strength, high-formability aluminum alloy with excellent SCC resistance according to claim 1, which is an aluminum alloy containing one or more of the following.