JPH0247234A - High strength aluminum alloy for forming having suppressed age hardenability at room temperature and its manufacture - Google Patents

Abstract

PURPOSE:To obtain the title Al alloy having excellent formability and suppressed age hardenability and in which the lowering of strength after baking finish is prevented by incorporating trace amounts of Zn into an Al-Cu-Mg alloy having specific compsn., subjecting it to low temp. rolling and thereafter to final solution heat treatment. CONSTITUTION:An Al alloy contg., by weight, 4 to 6% Mg, 0.2 to 1.2% Cu, <10% Mg+5Cu, 0.04 to 0.50% Zn, 0.01 to 0.05% Ti and 0.0001 to 0.0100% Be is cast. The alloy is subjected to one-stage or multistage homogenizing treatment at 400 to 550 deg.C for 2 to 48hr and is subjected to solution heat treatment. Or, without the solution heat treatment, it is subjected to hot working in the deposition temp. range of <=440 deg.C. The alloy is then subjected to cold working into prescribed plate thickness, is thereafter rapidly heated to 480 to 550 deg.C and is subjected to final solution heat treatment. After rapid cooling, the alloy is subjected to weak working such as roll straightening and skin pass rolling. By this method, the high hardness Al alloy for forming in which the generation of stretcher strain marks is prevented and the age hardening at room temp. is suppressed can be obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an Al-Mg-Cu-Zn alloy with excellent formability and a method for producing the same, and particularly to an Al-Mg-Cu-Zn alloy that suppresses room temperature age hardening and Baking relates to an aluminum alloy that prevents strength loss after painting and its manufacturing method.

[Prior Art] Conventionally, mild steel plates have been widely used as automobile body materials, but aluminum alloy plates have come to be used to reduce the weight of car bodies. This aluminum alloy is 5182
, X5085, etc., AU2G, 203
Heat-treated alloys such as 6.2002.6009.6010 have been put into practical use. The strength of these alloys is approximately the same as that of conventional cold-rolled steel sheets used for automobiles, but they have the disadvantage of poor press formability, and various proposals have been made to overcome this disadvantage. being done. AI-Mg-Cu-Zn with both strength and formability
system alloy and its containing Mn, Cr, Zr, and V (Special Publication No. 5B-31858, Japanese Patent Publication No. 5B-3i)
No. 880), an alloy containing Be in the Al-Mg-Cu-Zn system (Japanese Patent Publication No. 80-50854) with improved strength, formability, and bending workability. A method for preventing the occurrence of strain marks (Japanese Patent Application No. 61-IH519) has been proposed.

[Problems to be Solved by the Invention] However, although these materials are said to have excellent formability, they all contain ZnSCu to increase their strength through age hardening, and before press forming, they must be age hardened at room temperature. It is undeniable that the strength is higher than when shipped, and the moldability is relatively poor. In recent years, press forming conditions have become quite severe, and plate materials with better press formability are required more than ever before.

Therefore, the purpose of the present invention is to have low strength before press forming.
The purpose of the present invention is to provide a material whose strength does not decrease even when the paint is baked after press forming.

[Means for Solving the Problems] To summarize the structure of the present invention for achieving the above object, Mg: 4 to 6%, Cu: 0.2 to 1.2% on a weight basis.
, Mg+5Cu: 10%, Zn: 0.04~
0.50%, Ti: 0.01-0.05%, Be: 0.0001-0.0100%, and the remainder consists of Al and unavoidable impurities. High-strength molding with suppressed room temperature age hardenability. Aluminum alloy for use, or the components of this alloy further include M n % Cr SZ r s
0602 to 0.20% of any one or more of V
The above aluminum alloy containing the aluminum alloy and the aluminum alloy having any of the above metal compositions are 400 to 550%
After single-stage or multi-stage homogenization treatment at 2 to 48 hours at ℃, hot working is performed in a precipitation temperature range of 440 ℃ or less with or without solution treatment before hot working, and then , after cold working to a predetermined thickness and quenching to 480-550°C, gentle processing such as roller straightening or skin pass rolling is performed to prevent the occurrence of stretcher strain marks and to achieve high strength with suppressed room temperature age hardenability. This is a method for producing an aluminum alloy for forming.

Next, the reason for limiting these alloy components will be described.

Mg: Mg is an essential element mainly for increasing strength and ductility, and is in the range of 4 to 6%. If it is less than 4%, strength and formability are insufficient, and if it exceeds 6%, hot workability deteriorates and rolling cracks are likely to occur.

Cu: Cu is an element that imparts hardness and increases strength, and particularly improves strength after paint baking and suppresses the occurrence of stretcher strain marks, and should be in the range of 0.2 to 1.2%. If it is less than 0.2%, the effect is small; 1.
If it exceeds 2%, the strength will be significantly increased, but problems will arise in hot workability and formability, and it will also cause a decrease in the corrosion resistance of the material.

M g + 5 Cu; M g + 5 Cu is 1
If it exceeds 0%, hot working cracks are likely to occur.

Zn: Zn is an element that improves hot workability, increases strength and prevents stretcher strain marks.
This is set to be in the range of 0.04 to 0.50%. By containing such a small amount, room temperature age hardening is suppressed, and the range is set such that age hardening does not occur even after about half a year. 0.
If the Cu content is less than 0.04%, baking will cause a decrease in strength after coating, and if it exceeds 0.5%, the product will age harden at room temperature, causing problems in formability.

Ti; Ti is effective in refining the crystal grains of the ingot, and 0
．． 01 to 0.05%.

If it is less than 0.01%, the effect will be small, and if it exceeds 0.05%, huge crystallized substances will be produced, which is not preferable.

Be: Be is effective in preventing oxidation of the molten metal during melting and casting, and is particularly essential as the Mg content increases.

If it is less than 0.0001%, the effect is small, and 0.010%
If it exceeds 0%, its toxicity becomes a problem.

Mn, Cr, Zr, V; Mn, Cr, Zr, and V are included as necessary, and are effective for refining recrystallized grains and improving strength, and are 0.02
-0.2% range. However, both are 0.02%
If it is less than 0.062%, these effects will not be obtained, and if it exceeds 0.62%, recrystallization will become too fine and stretcher strain marks will occur, resulting in poor quality. It also has the disadvantage of producing large intermetallic compounds.

Next, the reason for limiting these manufacturing conditions will be described.

(1) Homogenization treatment of the ingot; Homogenization treatment of the ingot can easily segregate during casting.
M for the effect of making Cu and Zn homogeneous and for finer recrystallization
This has the effect of sufficiently precipitating transition elements such as n, Cr5Zr, and V. For this purpose, it is heated and held at 400-500°C for 2-48 hours. In order to fully exhibit these effects, multi-stage heat treatment may be performed. The heating temperature is 40
If it is below 0°C, the effect of homogenizing the ingot is small, and if it exceeds 550°C, the surface of the ingot is likely to be oxidized, and there is a possibility that a part of the segregated phase may undergo eutectic melting. In addition, if it is less than 2 hours, the effect of homogenizing the ingot is small, and if it is more than 48 hours, the homogenizing effect is saturated and is industrially meaningless.

(2) Solution treatment: Solution treatment is performed during heating after homogenization treatment and before hot rolling, and may not be performed for the reasons described below. Homogenization of the ingot and heating before hot rolling are usually performed separately. A I -M g -Cu-based compound (
S phase) is often precipitated, and these precipitates usually tend to precipitate at grain boundaries and easily cause hot cracking during rolling. Moreover, if the precipitates are coarse, they become a cause of a decrease in strength during solution treatment in the final solution treatment. For this reason, it is preferable to heat to a solution treatment temperature of 450° C. or higher in order to re-dissolve the compound precipitated during cooling after the homogenization treatment. If it is less than 450°C, this effect cannot be obtained, and if it exceeds 550°C, eutectic melting will occur, which is not preferable. Further, it is possible to perform rolling without performing solution treatment as long as the rolling temperature is low. However, in this case, S
Since some of the phases have precipitated, it is preferable to lengthen the holding time in the final solution treatment.

(3) Rolling temperature: After the solution treatment, it is cooled to 440° C. or lower, and hot working is started in the temperature range where the S phase precipitates. If rolled at a temperature exceeding 440° C., recrystallization tends to occur, and if the rolling speed is increased, grain boundary precipitation is likely to occur, causing hot cracking. For this reason, it is necessary to keep the hot working temperature to 440° C. or lower.

If the temperature is below 200°C, the deformation resistance becomes high, which is not preferable.

(4) Final thermal refining; Industrially, the final thermal refining is a solution quenching treatment using a continuous annealing heating furnace. In this case, the temperature is generally high and short. For this purpose, the material is heated to a temperature of 480 to 550 DEG C. for a short period of time to be quenched. If the heating temperature is less than 480°C, recrystallization may not occur, and if it exceeds 550°C, eutectic melting tends to occur, which is not preferable.

(5) Mild cold processing; Prevents stretcher strain marks after quenching! To achieve this, gentle processing such as roller leveling or skin pass rolling is performed.

[Example] The present invention will be explained below with reference to Examples.

Example 1 An alloy having the components shown in Table 1 below was formed into an ingot by a normal melting method. The homogenization treatment was performed by holding at 420°C for 2 hours and at 500°C for 8 hours, followed by furnace cooling. In addition, No. 5 to which Zr was added
．． 8, 9, 10, 11°21 further becomes 24 at 550°C.
Added time homogenization process. Before hot working, it was reheated at 500°C for 1 hour, air cooled to 420°C, and after solution treatment, hot working was started. Thereafter, a plate having a thickness of IIIR was obtained through a cold rolling process. In the final solution treatment, the temperature was maintained at 540° C. for 30 seconds in a salt bath, followed by cooling with a fan. After that, a 1% skin pan was added and a tensile test was performed, and the 0.2% yield strength was measured and the surface condition (rough skin, stretcher strain marks) at the point when the elongation reached 326 during the tensile test in the rolling direction. The presence or absence) was investigated. Also,
The room temperature age hardenability after being left at room temperature for 3 months, and the age hardenability when heated at 170°C for 30 minutes, which corresponds to painting baking, were investigated by changes in 0.2% proof stress in a tensile test. Room temperature age hardenability and paint baking hardenability are expressed as + and - decreases based on the yield strength after skin pass rolling, and the results are shown in Table 1. If a crack occurred during hot rolling, further testing was discontinued.

As an evaluation, hot processing is possible, there is no surface roughness or stretcher strain marks when the elongation reaches 3% during the tensile test, and the yield strength change is 0.5 kg 3 months after skin pass. /mm2 or less, and the increase in yield strength after heating at 170°C for 30 minutes after skin pass is 1.0
The present invention includes those having a weight ratio of kg/m m2 or more.

Nα14 has a high Zn content, and the change in yield strength 3 months after skin pass is as high as 1.6 kg/mm'.

In No. 15, Cu; Zn was not added, so when the elongation reached 3% during the tensile test, roughness occurred on the surface due to coarsening of crystal grains, and the surface condition was poor.

No. 16 is high in Cu and M g + 5 Cu, No. 17 is high in Mg and M g + 5 Cu, and No. 18 is high in Mg, Cu and M g +
5 Cu was high, hot rolling cracking occurred in all cases, and the test was discontinued.

No. 19 has a high Mn content (No. 20 has a high Cr content), and in both cases, roughness due to stretcher strain marks occurred on the surface when the elongation reached 396 during the tensile test, and the surface condition was poor.

N (L21 had high Zr (, No. 22 had high ■), and in both cases, the homogenization treatment coarsened the crystallized substances, making rolling impossible, and the test was discontinued.

No. 23 has low Cu and after skin pass [70°C
There is little increase in yield strength after heating for 30 minutes.

No. 24 has a high Mg+5CLJ of 10.596 and causes rolling cracks.

Since Ti is not added to Nα25, the casting composition is not densified and rolling cracks occur.

No. 26 has no Ti and Be added, so
The casting surface of the ingot is poor, and the casting structure is not densified, causing rolling cracks.

Example 2 Using some of the materials shown in Table 1, manufacturing was carried out with various conditions for homogenization treatment, solution treatment, hot rolling, cold rolling, final solution treatment, and weak working. Table 2 shows the results of tests similar to those shown in the table.

Nα31 to Nα38 are within the scope of the present invention, and hot heating is possible, and when the elongation reaches 3% in the tensile test, rough skin and stretcher strain marks will not occur on the surface. 3 months after skin pass, the change in yield strength is less than 0.5 kg/mm', and the increase in yield strength after heating at 170℃ for 30 minutes after skin pass is 1.0.
kg/mm' or more, which is within the evaluation range.

For Nα39, the test was discontinued due to the low homogenization temperature and the occurrence of edge cracks.

For Nα40, the homogenization temperature was high, and eutectic melting was observed after the homogenization treatment.

For Nα41, the homogenization treatment time was short and the test was discontinued due to the occurrence of edge cracking.

In No. 42, the final solution treatment temperature was low and stretcher strain marks occurred.

For Nα43, the final solution treatment temperature was high, and some melting was observed.

Since Nα44 was not subjected to mild processing after the final solution treatment, stretcher strain marks were generated.

[Effect of the invention] As explained above, the present invention provides Al-M g -C
We present an aluminum alloy that has excellent formability, suppresses the aging effect at room temperature, and prevents the strength from decreasing after painting by incorporating a small amount of Zn into a u-based alloy and further performing low-temperature rolling, and a method for producing the same. I was able to share one with you.

Patent Applicant Sumitomo Light Metal Industries Co., Ltd. Agent Patent Attorney Hidetake Komatsu Agent Patent Attorney Hiroshi Asahi Agent Patent Attorney Mikio Kaga

Claims (4)

[Claims] (1) In weight%, Mg: 4-6% Cu: 0.2-1.2% Mg+5Cu: <10% Zn: 0.04-0.50% Ti: 0.01-0.05% Be: A high-strength forming aluminum alloy with suppressed room temperature age hardenability, characterized by containing 0.0001 to 0.0100% and the remainder consisting of Al and unavoidable impurities. (2) In weight%, Mg: 4-6% Cu: 0.2-1.2% Mg+5Cu: <10% Zn: 0.04-0.50% Ti: 0.01-0.05% Be: 0.0001 to 0.0100%, and further includes Mn: 0.02 to 0.20% Cr: 0.02 to 0.20% Zr: 0.02 to 0.20% V: 0.02 to 0 A high-strength forming aluminum alloy with suppressed room-temperature age hardenability, characterized by containing at least one of the above .20% and the remainder consisting of Al and unavoidable impurities. (3) In weight%, Mg: 4-6% Cu: 0.2-1.2% Mg+5Cu: <10% Zn: 0.04-0.50% Ti: 0.01-0.05% Be: An aluminum alloy containing 0.0001 to 0.0100% was heated at 400 to 550°C for 2
After single or multi-stage homogenization treatment for ~48 hours,
With or without solution treatment before hot working, 4
Hot working is performed in a precipitation temperature range of 40°C or less, and then
Stretcher strain marks characterized by cold working to a predetermined thickness, rapid heating to 480 to 550°C, final solution treatment, rapid cooling, and then mild processing such as roller straightening or skin pass rolling. A method for producing a high-strength forming aluminum alloy that prevents the occurrence of and suppresses room temperature age hardenability. (4) In weight%, Mg: 4-6% Cu: 0.2-1.2% Mg+5Cu: <10% Zn: 0.04-0.50% Ti: 0.01-0.05% Be: 0.0001 to 0.0100%, and further includes Mn: 0.02 to 0.20% Cr: 0.02 to 0.20% Zr: 0.02 to 0.20% V: 0.02 to 0 Ameminium alloy containing at least one of .20% and the remainder consisting of Al and unavoidable impurities,
After single-stage or multi-stage homogenization treatment at 2 to 48 hours at °C, hot working is performed in a precipitation temperature range of 440 °C or less, with or without solution treatment before hot working, and then, Stretcher strain marks characterized by cold working to a predetermined thickness, rapid heating to 480 to 550°C, final solution treatment, rapid cooling, and then mild processing such as roller straightening or skin pass rolling. A method for producing a high-strength forming aluminum alloy that prevents the occurrence of and suppresses room temperature age hardenability.