JPH0860315A - Production of aluminum alloy sheet for forming - Google Patents

Abstract

PURPOSE: To produce an Al alloy sheet for forming, reduced in secular change at room temp. and excellent in formability and baking hardenability. CONSTITUTION: An ingot of an alloy, having a composition consisting of 0.3-1.5% Mg, 0.4-2.0% Si, >0.4-1.4% Cu, one or >=2 kinds among 0.03-1.5% Zn, 0.03-0.4% Mn, 0.03-0.4% Cr, 0.03-0.4% Zr, 0.03-0.4% V, 0.03-0.5% Fe, and 0.005-0.2% Ti, and the balance essentially Al, is used. This ingot is homogenized, hot-rolled, and cold-rolled. The resulting alloy sheet is subjected to solution heat treatment at >=480 deg.C, cooled to 45-75 deg.C at a rate of >=100 deg.C/min, held at the temp. for a time in the range not shorter than 5sec and capable of controlling the proof stress of the alloy to <=105N/mm<2> , and successively subjected to stabilizing treatment at 80-150 deg.C for 0.5-40hr.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aluminum alloy sheet, which is used as a raw material for automobile body sheets, parts, various machines and appliances, home electric appliances, etc. after being subjected to molding and baking. In particular, the present invention relates to a method for producing an aluminum alloy sheet for forming, which has good formability, high strength after coating baking, and little change with time at room temperature.

[0002]

2. Description of the Related Art Conventionally, cold rolled steel sheets have been mainly used for body sheets of automobiles, but recently, rolled aluminum alloy sheets have been used from the viewpoint of reducing the weight of a vehicle body. Because the body sheet of an automobile is used after being pressed, it must have excellent moldability and not have any Rudermark during molding, and it must have high strength. In particular, since paint baking is performed, it is required that high strength be obtained after paint baking.

Conventionally, as such an aluminum alloy for an automobile body sheet, JIS having aging properties is used.
No. 6000 series alloy, that is, Al-Mg-Si based alloy is mainly used. This aging Al-Mg-Si
Based alloys have relatively low strength during molding before baking, and have excellent formability.On the other hand, they have the advantage of being aged by heating during baking to increase strength after baking. It has advantages such as the generation of dozen marks.

By the way, as a method for producing an Al--Mg--Si alloy plate, which is expected to age harden during baking,
After homogenizing and heat-treating the ingot, hot rolling and cold rolling are performed to a predetermined plate thickness, and if necessary, intermediate annealing is performed between hot rolling and cold rolling or in the middle of cold rolling. It is usual to carry out a solution treatment after cold rolling and quenching. However, it is difficult for such a conventional general manufacturing method to sufficiently satisfy the characteristics required for recent automobile body sheets.

That is, recently, there has been a strong demand for a further reduction in thickness in order to further reduce the cost. For this reason, a further increase in strength has been required so that sufficient strength can be obtained even with a thin wall. In this respect, the Al-Mg-Si alloy plate obtained by the conventional general manufacturing method is insufficient.

Regarding coating baking, in order to save energy and improve productivity, and in combination with a material such as a resin which is not preferably exposed to a high temperature, the baking temperature is made lower than before, and There is an increasing tendency to shorten the baking time. Therefore, in the Al-Mg-Si alloy plate obtained by the conventional general manufacturing method, the curing at the time of baking the coating (baking hardening) is insufficient, and there is a problem that it becomes difficult to obtain sufficient high strength after baking the coating. . In addition, conventional Al-Mg-
In Si-based alloy sheets, if the bake hardenability is to be increased in order to obtain high strength after painting and baking, hardening tends to occur due to natural aging when left at room temperature after the sheet is manufactured, which tends to hinder the formability. There is also the problem that

[0007]

SUMMARY OF THE INVENTION The present invention has been made under the circumstances described above, and it has good moldability and at the same time has excellent bake hardenability, resulting in high strength increase during coating baking. Moreover, there is little change over time at room temperature after plate production, and it is an object of the present invention to provide a method for producing an aluminum alloy plate for forming process in which there is little deterioration in formability due to hardening due to natural aging even when left for a long time. To do.

[0008]

Means for Solving the Problems As a result of repeated experiments and studies by the present inventors in order to solve the above problems, Al-
The inventors have found that the above-mentioned problems can be solved by appropriately selecting the component composition of the Mg-Si alloy and at the same time performing an appropriate heat treatment after the solution treatment during the plate manufacturing process, and have completed the present invention. It was

Specifically, the method for producing an aluminum alloy plate according to the present invention uses Mg 0.3 to 1.5% and Si 0.4 to
2.0%, containing more than Cu 0.4% and 1.4% or less,
And Zn 0.03 to 1.5%, Mn 0.03 to 0.4
%, Cr 0.03 to 0.4%, Zr 0.03 to 0.4
%, V0.03-0.4%, Fe0.03-0.5%,
An alloy containing one or more selected from 0.005 to 0.2% Ti and the balance being Al and unavoidable impurities is used as a raw material, and the ingot is homogenized, hot-rolled and cooled. Hot rolling to a rolled plate having a required plate thickness, the solution rolling treatment is performed on the rolled plate at a temperature of 480 ° C. or higher, and then 45 to 7 at a cooling rate of 100 ° C./min or higher.
After cooling to a temperature range of 5 ° C, holding for 5 seconds or more within this temperature range, and limiting the upper limit of the holding time so that the proof stress (σ _0.2 ) of the alloy is 105 N / mm ² or less, Then heat to a temperature in the range of 80-150 ° C,
It is characterized in that a stabilizing treatment is carried out for holding in this temperature range for 0.5 to 40 hours.

[0010]

First, the reasons for limiting the composition of the alloy used in the manufacturing method of the present invention will be described.

Mg: Mg is a basic alloying element in the alloy of the system targeted by the present invention, and contributes to the strength improvement in cooperation with Si. When the amount of Mg is less than 0.3%, Mg ₂ Si contributes to strength improvement by precipitation hardening at the time of coating baking.
Since the amount of M produced is small, sufficient improvement in strength cannot be obtained. On the other hand, if it exceeds 1.5%, the formability is deteriorated.
The amount of g was set within the range of 0.3 to 1.5%.

Si: Si is also a basic alloying element in the alloy of the present invention, and contributes to improvement in strength in cooperation with Mg. Further, Si is generated as a crystallized product of metallic Si during casting, and the periphery of the metallic Si particles is deformed by processing to become a recrystallization nucleus generation site during solution treatment, so that the fine recrystallization structure is fine. Also contributes to Si is 0.4%
If it is less than 2.0%, the above effect cannot be sufficiently obtained, while if it exceeds 2.0%, coarse Si is generated and the toughness of the alloy is lowered. Therefore, Si is set within the range of 0.4 to 2.0%.

Cu: Cu is an element effective in promoting age hardening and increasing the strength of the alloy. If the Cu content is 0.4% or less, the effect is not sufficiently obtained, while if it exceeds 1.4%, the corrosion resistance decreases, so that Cu exceeds 0.4% and 1.4
It was set within the range of% or less.

Zn, Mn, Cr, Zr, V, Ti, F
e: These are added in one kind or two or more kinds in order to improve the strength and refine the crystal grains. Of these, Zn is an element that contributes to the strength improvement through the improvement of the aging property of the alloy, and if the content thereof is less than 0.3%, the above effect is insufficient, while if it exceeds 1.5%, it is formed. Since the corrosion resistance and the corrosion resistance decrease, the Zn content in the case of adding Zn is 0.03 to
It was set within the range of 1.5%. Furthermore, Mn, Cr, Zr, V
Is an element effective in improving the strength, refining the crystal grains and stabilizing the structure.
If it is less than 0.1%, the above effect cannot be sufficiently obtained, while if it exceeds 0.4%, not only the above effect is saturated, but also a huge intermetallic compound may be formed, which may adversely affect the formability. Therefore, Mn, Cr, Zr, and V are all within the range of 0.03 to 0.4%. Also Ti
Is an element effective in improving strength and refining the ingot structure. If the content is less than 0.005%, a sufficient effect cannot be obtained, while if it exceeds 0.2%, the effect of Ti addition is saturated. Not only that, but there is a possibility that huge crystallized substances may occur,
Ti was made into the range of 0.005-0.2%. And Fe is also an element effective in improving strength and refining crystal grains,
If the content is less than 0.03%, a sufficient effect cannot be obtained, while if it exceeds 0.5%, the formability may be deteriorated. Therefore, Fe is in the range of 0.03 to 0.5%. did. These Zn, Mn, Cr, Zr, V, T
The ranges of i and Fe are shown for the case where these elements are included as positively added elements, and it is not a particular problem that both of them contain less than the lower limit value thereof as impurities. In particular, Fe of less than 0.03% is usually unavoidably contained by using a normal aluminum base metal.

In addition to the above elements, basically Al and unavoidable impurities may be used. However, in general, a small amount of Be may be added to a Mg-containing alloy in order to prevent oxidation of the molten metal. In the case of the alloy according to the present invention, addition of about 0.0001 to 0.01% of Be is also required. Permissible. Further, in general, B may be added at the same time as Ti described above for refining the crystal grains, and in the case of the present invention as well, it is permissible to add B in an amount of 500 ppm or less together with Ti.

Next, the manufacturing process in the method of the present invention will be described.

The process up to the solution treatment, that is, the process for forming a rolled plate having a required product plate thickness, is the same as in the conventional J.
It may be the same as the IS 6000 series Al-Mg-Si series alloy. That is, after casting by a DC casting method or the like, homogenization treatment may be performed by an ordinary method, and hot rolling and cold rolling may be performed to obtain a required sheet thickness. In addition, hot rolling and cold rolling may be performed. Alternatively, intermediate annealing may be performed as needed in the middle of cold rolling.

After the required product plate thickness is obtained as described above, solution treatment is performed at a temperature of 480 ° C. or higher. In this solution treatment, Mg ₂ Si or the like is solid-dissolved in the matrix,
This is a step necessary for imparting bake hardenability and improving the strength after baking for coating, and is also a step for recrystallizing to obtain good formability. If the solution treatment temperature is lower than 480 ° C., the solid solution amount of Mg ₂ Si is small and sufficient bake hardenability cannot be obtained. Although the upper limit of the solution treatment temperature is not particularly defined, it is usually desirable to be 580 ° C. or less in consideration of the possibility of eutectic melting and coarsening of recrystallized grains. The time for the solution treatment is not particularly limited, but is usually 120 minutes or less.

After the solution treatment, the material is cooled (quenched) to a temperature range of 45 to 75 ° C. at a cooling rate of 100 ° C./min or more. Here, the cooling rate after the solution treatment is 100 ° C.
If it is less than / min, a large amount of Mg ₂ Si will be precipitated during cooling, and the formability will decrease, and at the same time, the bake hardenability will decrease, making it impossible to expect a sufficient improvement in strength during baking of the coating.

After the solution heat treatment at a temperature of 480 ° C. or higher as described above, the solution is cooled at a cooling rate of 100 ° C./min or higher.
Cooling (quenching) in the temperature range of 5 to 75 ° C, and then 45 to 7
Hold for a time T within a temperature range of 5 ° C. This holding time T
Has a lower limit of 5 seconds and an upper limit (T _max ) of which the proof stress of the alloy is 10
Adjust so that it is 5 N / mm ² or less. Then, after holding for 5 seconds to T _max in the temperature range of 45 to 75 ° C in this way, it is heated again to a temperature in the range of 80 to 150 ° C,
Stabilization treatment is carried out by maintaining the temperature within this temperature range for 0.5 to 40 hours.

After solution treatment as described above, 45 to 75 ° C.
The reason for cooling to 5 seconds to hold T _max for 5 seconds is as follows. That is, after the solution treatment, especially 100 ° C./m
When cooled to a room temperature of less than 45 ° C. at a cooling rate of in or more, room temperature clusters are generated. This room temperature cluster contributes to the strength of G. P. Since it is difficult to move to the zone, the structure in which the room temperature cluster is formed is disadvantageous in the paint bake hardenability. On the other hand, when the solution is cooled to a temperature exceeding 75 ° C. and kept as it is after the solution treatment, high temperature clusters or G. P. Although a zone is formed and it is advantageous for the bake hardenability of the coating, it has a large change over time due to room temperature aging after the stabilization treatment, which adversely affects the formability. Therefore, from the viewpoint of the balance between formability and paint bake hardenability, it is necessary to quench within the temperature range of 45 to 75 ° C after the solution treatment. That is, 45 to 7 after solution treatment
By cooling within the temperature range of 5 ° C., both moldability and paint bake hardenability can be satisfied.

If the holding time T in the temperature range after cooling in the temperature range of 45 to 75 ° C. after the solution treatment is 5 seconds or less, the above effects, particularly the effect of suppressing room temperature aging, cannot be obtained. On the other hand, when the holding time T in the temperature range of 45 to 75 ° C. is long, a cluster having a structure and properties close to a room temperature cluster or G. P. A large number of zones are generated, and the subsequent paint bake hardenability deteriorates. Since the influence of the holding time T when holding for a long time depends on the alloy components until the solution heat treatment, the solution temperature, etc., the upper limit of the holding time T cannot be uniformly set, but the yield strength of the alloy is It can be set as an index. That is, if the holding time at 45 to 75 ° C. becomes long and a large amount of clusters are generated in that temperature range, the yield strength of the alloy also becomes high.
Of can define the upper limit T _max, according to the experiments of the present inventors, it proof stress is effective to restrict the upper limit T _max of the retention time T so as to be in the range of 105N / mm ² or less There was found. The yield strength is 1 after solution treatment.
It means the proof stress in a state of being cooled to a temperature range of 45 to 75 ° C. at a cooling rate of 00 ° C./min or more and being kept in that temperature range. Therefore, in actual operation, this proof stress is 1
The upper limit T of the holding time T such that it becomes less than or equal to 05 N / mm ^2.
The specific value of _max may be obtained by conducting a preliminary experiment according to actual specific conditions such as alloy composition and solution treatment temperature.

After holding in the temperature range of 45 to 75.degree. C. as described above, the temperature of 80 to 80.degree.
Stabilization is performed by heating to a temperature in the range of 150 ° C. This stabilization process is finally performed on the cluster or G. P. This stabilization treatment is a step necessary for improving the stability of the zone, suppressing the change with time after plate production, ensuring sufficient bake hardenability and obtaining good moldability. ~ 0.5 to a temperature in the range of ~ 150 ℃
It is necessary to set the condition for holding for 40 hours. If the stabilization treatment temperature is lower than 80 ° C, the above effects cannot be sufficiently obtained, while if it exceeds 150 ° C, the material strength becomes high due to high temperature aging, and the formability deteriorates. Further, when the holding time at a temperature in the range of 80 to 150 ° C. in the stabilization treatment is less than 0.5 hours, the subsequent change with time at room temperature becomes fast and the moldability and bake hardenability deteriorate, while 40 hours If it exceeds, the material strength will increase due to aging, the moldability will decrease, and the productivity will be impaired.

As described above, in the production method of the present invention, the composition of the alloy components is appropriately adjusted, and during the production process, the solution treatment is performed at a temperature of 480 ° C. or higher, and the temperature range is set to 45 to 75 ° C. After cooling (quenching) and appropriate holding in that temperature range, the stabilizing treatment is performed again under the condition of 80 to 150 ° C. to change with time at room temperature after plate production, that is, the progress of natural aging at room temperature. As a result, it is possible to sufficiently secure good moldability and excellent bake hardenability even when the plate is left for a long period of time and then subjected to molding and coating baking. It was.

[0025]

EXAMPLES Alloys of alloy symbols A1 to A3 within the compositional range of the present invention shown in Table 1 and alloys of alloy symbols B1 to B2 outside the compositional range of the present invention were cast by a DC casting method according to a conventional method. , 530 ℃ × 5 to the obtained ingot
After carrying out the homogenizing treatment of h, hot rolling was started, and then cold rolling was carried out to obtain a rolled plate having a thickness of 1 mm. Next, each rolled plate is subjected to a solution treatment at 520 ° C. for 10 seconds, then quenched at various temperatures at a cooling rate of 100 ° C./min or more, and held at the quenching temperature, and further 80 to 150 ° C. Stabilization was performed at. Detailed conditions are shown in Table 2.

The plate obtained by subjecting the plate to the stabilization treatment as described above is further left to stand at room temperature for 1 day or 40 days, and each plate is subjected to coating baking treatment by heating at 180 ° C. × 60 minutes, and The mechanical properties and formability before baking and the mechanical properties after baking were examined. Table 3 shows the results.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

Production Nos. 1 to 3 are those in which the composition of the alloy is within the range specified by the present invention and the manufacturing conditions also satisfy the conditions specified by the present invention. The elongation before coating baking and the Erichsen value are sufficiently high, the moldability is excellent, and the bake hardenability is high, and a large increase in strength occurs during coating baking, and even when left at room temperature for 40 days after plate production, The elongation and Erichsen value did not decrease so much that the moldability did not decrease, and sufficient bake hardenability was exhibited.

On the other hand, in Production Nos. 4 to 7, the alloy composition was within the range specified by the present invention, but the production conditions did not satisfy the conditions specified by the present invention. And manufacturing number 4 (alloy code A1) is what was cooled to room temperature (25 ° C.) after solution treatment, but in this case, the same alloy (alloy code A1) was used as an example of the present invention (manufacturing number 1). Bake hardenability was inferior compared with. Serial number 5
(Alloy symbol A2) has a proof stress of 105 N at the time of holding because the holding time at 55 ° C. after solution treatment-cooling was too long.
/ Mm ² and in this case the same alloy (alloy code A
The bake hardenability was inferior to the invention example (Production No. 2) using 2). Further, in the production number 6 (alloy symbol A3), since the quenching temperature was too high, the change with time due to room temperature aging after the production was large as compared with the invention example (production number 3).
After the day, sufficient bake hardenability was not obtained. Further, in the production number 7 (alloy symbol A2), the temperature of the stabilization treatment was too high and the holding time of the stabilization treatment was too short. In this case, the invention example (production number 2) was used. In comparison, the secular change due to aging at room temperature was large, and sufficient bake hardenability was not obtained.

On the other hand, the production numbers 8 and 9 are applied to the alloys whose component compositions are out of the range specified by the present invention, and the processes under the conditions specified by the present invention are applied. In this case, Not only was the material strength low in all cases, but also the bake hardenability was low, and the strength after baking was not sufficiently obtained.

[0033]

EFFECTS OF THE INVENTION According to the method for producing an aluminum alloy sheet for forming of the present invention, the formability is excellent, the bake hardenability is excellent, and the strength after baking is extremely high.
Moreover, it is possible to obtain a stable aluminum alloy sheet for forming, which has little change with time at room temperature, has little deterioration in formability even after being left at room temperature for a long time after production, and has little change in bake hardenability. Therefore, it is most suitable for the production of aluminum sheet for automobile body sheets, home electric appliance parts, various machine / equipment parts, and other applications for which molding and painting are applied.

Claims (1)

[Claims] 1. Mg 0.3 to 1.5% (weight%, the same applies hereinafter), Si 0.4 to 2.0%, Cu 0.4% and more than 1.
4% or less, and Zn 0.03 to 1.5%, Mn
0.03-0.4%, Cr 0.03-0.4%, Zr
0.03-0.4%, V0.03-0.4%, Fe0.
An alloy containing one or more selected from 03 to 0.5% and Ti 0.005 to 0.2%, with the balance being Al and unavoidable impurities, and homogenized into an ingot. Processing, hot rolling and cold rolling to obtain a rolled plate having a required plate thickness, and the rolled plate is subjected to solution treatment at a temperature of 480 ° C. or higher and then cooled at a cooling rate of 100 ° C./min or higher to 45 It is cooled to a temperature range of up to 75 ° C and held for 5 seconds or longer within this temperature range, and the upper limit of the holding time is regulated so that the yield strength (σ _0.2 ) of the alloy is 105 N / mm ² or less. Then, the composition is heated to a temperature in the range of 80 to 150 ° C. and then subjected to a stabilizing treatment in which the temperature is maintained in this temperature range for 0.5 to 40 hours. And aluminum for molding with excellent bake hardenability Method of manufacturing a gold plate.