JPH05202454A - Manufacture of baking hardenability aluminum alloy sheet for forming - Google Patents

Abstract

PURPOSE:To provide an Al alloy sheet for forming which is used for an automobile exterior plate or the like, facilitates the solution heat treatment in a continuous annealing equipment and has high baking hardenability. CONSTITUTION:An Al alloy contg., by weight, 0.2 to 3.0wt.% Si and 0.2 to 3.0wt.% Mg, furthermore contg., as necessary 0.01 to 1.5wt.% Cu and 0.01 to 0.25wt.% Fe and, moreover, contg., if desired, total 0.01 to 1.0wt.% of one or >=two kinds among 0.01 to 0.3wt.% Mn, 0.01 to 0.5wt.% Cr, 0.01 to 0.5wt.% Zr, 0.01 to 0.5wt.% Ti and 0.01 to 0.3wt.% Ni, and the balance Al with inevitable impurities is subjected to hot rolling or cold rolling, is subsequently subjected to heat treatment at >=480 deg.C, is thereafter subjected to cold rolling, is subjected to solution heat treatment at >=400 deg.C and is cooled at >=3 deg.C/sec cooling rate to manufacture the objective Al alloy sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention has excellent bake hardenability, and is required to have strength for automobile outer plates and packaging plate materials.
In addition, the present invention relates to a method for producing a bake-hardenable aluminum alloy sheet for forming, which is suitable for a member to be baked and coated.

[0002]

2. Description of the Related Art Conventionally, cold-rolled steel sheets have been mainly used for automobile outer panels. However, recently, the use of an aluminum alloy plate has been studied due to the demand for weight reduction of an automobile body, and it has been partially put into practical use. Materials for automobile outer panels are required to have excellent press formability, high strength, and excellent corrosion resistance. As a material satisfying such requirements, 5052 (Al-2.5wt
% Mg-0.25wt% Cr) alloy, 5182 (Al-0.35wt% M)
Al-Mg alloy (5000 series alloy) such as n-4.5 wt% Mg) or 6009 (Al-0.8 wt% Si-0.6 wt% Mg-0.
33wt% Cu-0.5wt% Mn) alloy, 6061 (Al-0.6wt
% Si-1.0 wt% Mg-0.28 wt% Cu-0.2 wt% Cr)
Al-Mg-Si alloys (6000 series alloys) such as alloys have been used.

[0003]

The above 6000 series alloys have relatively good press formability and can obtain high strength after baking coating, and thus have been conventionally applied to outer panel materials of automobiles.
The heat treatment type aluminum alloy sheet material used for such a purpose is usually subjected to solution treatment by continuous annealing equipment. However, in this conventional method, since the holding time at the solution temperature is short, the solution may not be sufficiently solutionized. The conventional paint baking temperature for automobiles was 180 ° C for about 1 hour, but there is a tendency for the paint baking temperature to be lower and shorter, so high strength after baking is required. However, since the solution treatment in the continuous annealing equipment is insufficient, the baking effect at low temperature and in a short time is small.

[0004]

As a result of various studies in view of the above, the present invention has developed a method for producing a bake hardenable aluminum alloy sheet for bake hardenability, which facilitates solution treatment in continuous annealing equipment and has a high bake hardenability. It was done.

That is, one of the manufacturing methods of the present invention is that Si 0.2-
An aluminum alloy containing 3.0 wt% (hereinafter wt% is abbreviated as%) and Mg 0.2 to 3.0% and the balance Al and unavoidable impurities is subjected to heat treatment at 480 ° C. or higher after hot rolling or cold rolling, and further, It is characterized in that after cold rolling, solution treatment is performed at 400 ° C or higher and cooling is performed at a cooling rate of 3 ° C / sec or higher.

Another one of the manufacturing methods of the present invention is Si
An aluminum alloy containing 0.2 to 3.0%, Mg 0.2 to 3.0%, Cu 0.01 to 1.5%, and the balance Al and unavoidable impurities is subjected to heat treatment at 480 ° C or higher after hot rolling or cold rolling, and further cooling. It is characterized by performing solution treatment at 400 ° C or higher after hot rolling and cooling at a cooling rate of 3 ° C / sec or higher.

Another one of the manufacturing methods of the present invention is Si
0.2-3.0%, Mg 0.2-3.0%, Fe0.01-0.25%, Mn0.01-0.3%, Cr0.01-0.5%, Zr
An aluminum alloy containing 0.01 to 0.5%, 0.01 to 0.5%, and 0.01 to 0.3% of Ni, 0.01 to 0.3%, and 0.01 to 1.0% in total, and the balance Al and inevitable impurities are hot-rolled. Alternatively, it is characterized in that after cold rolling, heat treatment is performed at 480 ° C or higher, and further cold rolling is performed, then solution treatment is performed at 400 ° C or higher, and cooling is performed at a cooling rate of 3 ° C / sec or higher. ..

Still another one of the manufacturing methods of the present invention is Si
0.2-3.0%, Mg 0.2-3.0%, Cu 0.01-1.5%,
Fe0.01-0.25%, Mn0.01-0.3%, Cr
0.01-0.5%, Zr0.01-0.5%, Ti0.01-0.5%,
Ni 0.01 to 0.3% of one or two or more total 0.01 to
Aluminum alloy containing 1.0% and balance Al and unavoidable impurities is hot-rolled or cold-rolled, then heat-treated at 480 ° C or higher, then cold-rolled, and then solution-treated at 400 ° C or higher. It is characterized by cooling at a cooling rate of 3 ° C./sec or more.

[0009]

In the manufacturing method of the present invention, the alloy composition is limited as described above for the following reason. Si precipitates Mg ₂ Si together with Mg during baking coating to improve the strength. However, the addition amount is limited to 0.2 to 3.0% because if it is less than 0.2%, its effect is small, and if it exceeds 3.0%, the formability after solution treatment deteriorates.

Since Mg is a solid solution in the matrix after the solution treatment, it contributes to the improvement of formability and also precipitates Mg ₂ Si together with Si during baking coating to improve the strength.
The reason why the addition amount is limited to 0.2-3.0% is
If it is less than 0.2%, the effect is small, and if it exceeds 3.0%, the formability after solution treatment is deteriorated.

As described above, Si and Mg are M during baking coating.
It precipitates as g ₂ Si and improves the strength. However, if the abundance ratios of these two elements are different, the bake hardenability is also different.
If the amount of Si is excessive with respect to the amount of g ₂ Si, more excellent bake hardenability can be obtained. It should be noted that addition of Ag, Cd, etc. to control the aging behavior during baking coating does not impair the effects of the present invention.

Cu is used in the GP zone, θ ', and
Precipitation of S phase etc. improves the strength. The reason why the addition amount is limited to 0.01 to 1.5% is that if it is less than 0.01%, the strength is not improved so much, and if it exceeds 1.5%, not only the corrosion resistance decreases but also the quenching sensitivity becomes too high. Fe
Is usually contained as an impurity of Al. However, Fe easily forms a compound with Si, and if contained in excess of 0.25%, it hinders the improvement of strength during baking coating. Meanwhile 0.
If it is less than 01%, the effect is saturated and it is economically disadvantageous.

Mn, Cr, Zr, Ti and Ni are added to refine the crystal grains or improve the matrix strength. However, if it is less than the lower limit, the effect is small, and if it exceeds the upper limit, the formability after solution treatment is deteriorated. Further, if the total amount of these elements exceeds 1.0%, the formability after solution treatment deteriorates. If B or the like, which is usually added as a refinement material for the cast structure, is 0.1% or less, the effect of the present invention is not impaired.

Next, the manufacturing process of the present invention will be described.
The present invention melts an aluminum alloy having the above composition by a conventional method, forms an ingot by DC casting, homogenizes the ingot, and then hot-rolls the hot-rolled or hot-rolled and cold-rolled steel. After rolling, heat treatment at 480 ℃ or more, cold rolling, and solution heat treatment at 400 ℃ or more, 3 ℃ / se
Cool at a cooling rate of c or higher.

In the solution treatment, additional elements such as Si and Mg are once solid-solved in the matrix, and fine compounds such as Mg ₂ Si are precipitated during the subsequent baking and heating to improve the strength. Therefore, after hot rolling or cold rolling
Si, Mg before solution treatment after heat treatment at 480 ℃
By making the compound of the system fine and small, solid solution in a solution treatment for a short time is facilitated. Where the heating temperature is 4
The reason why the temperature is set to 80 ° C. or higher is that if the temperature is lower than 480 ° C., coarsening of the compound proceeds due to precipitation of Si and Mg, and rapid solution treatment becomes difficult, resulting in insufficient strength improvement after baking and heating. The holding time and the cooling rate are not particularly specified, but the holding time is preferably 1 hour or more and the cooling rate is preferably 3 ° C./sec or more.

The solution treatment temperature is set to 400 ° C. or higher because
If the temperature is less than 400 ° C, the additional elements cannot be sufficiently solid-dissolved, and the improvement in strength during baking and baking is small. The holding time is not particularly specified, but the time at which the temperature is 400 ° C. or higher is preferably 5 seconds or longer. Cooling rate after solution treatment is 3
C./sec. Or more is because a coarse compound is precipitated at a cooling rate of less than 3.degree. C./sec, so that the formability is lowered and the improvement in strength after baking is reduced.

[0017]

EXAMPLES The present invention will be described below with reference to examples. Table 1
The aluminum alloy of the composition shown in Figure 3
The ingot was cast to obtain an ingot, and the ingot was subjected to a homogenization treatment and then hot rolled into a plate material having a thickness of 7 mm. This plate material was cold-rolled at the rolling rate shown in Table 2, and also heat-treated and cold-rolled under the conditions shown in Table 2 to obtain a plate material having a thickness of 1 mm. Further, this plate material was subjected to solution treatment under the conditions shown in Table 2 and cooled at the rate shown in Table 2.

A tensile test, an Erichsen bulge test, and a limit deep drawing (LDR) test were conducted on the plate material thus manufactured. Also simulated the baking coating process 1
Tensile tests were conducted after heat treatment at 50 ° C, 180 ° C, and 200 ° C for 60 minutes each. The results are shown in Table 3. In the tensile test, tensile strength, proof stress and elongation were measured using JIS No. 5 test pieces. Erichsen overhang test is JIS Z2247A
The overhang height was measured by the method. Limit deep drawing (LDR)
In the test, a blank coated with lubricating oil was deep-drawn with a punch having a diameter of 33 mm, and the maximum blank diameter without breaking was divided by the punch diameter to obtain a value.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

[Table 3]

As is clear from Table 3, the production method (N
The plate materials of No. 1 to No. 10) are superior to the conventional manufacturing method (No. 21) both in formability after solution treatment and strength after baking coating treatment. On the other hand, it can be seen that the plate materials according to the comparative manufacturing method (No. 11 to No. 20) that deviates from the conditions of the present invention are inferior in any one or more of the above.

[0023]

As described above, according to the present invention, an aluminum alloy sheet material for molding having a high bake hardenability can be obtained, and a remarkable effect is industrially exhibited.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kunihiko Kishino 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Aluminum Co., Ltd. (72) Inventor Gen Watanabe 2-6-1, Marunouchi, Chiyoda-ku, Tokyo Furukawa Aluminum Co., Ltd.

Claims (4)

[Claims] 1. Si 0.2-3.0 wt%, Mg 0.2-3.0 wt
%, Aluminum alloy consisting of balance Al and unavoidable impurities is subjected to heat treatment at 480 ° C. or higher after hot rolling or cold rolling, and further cold rolling is performed, and then solution treatment is performed at 400 ° C. or more, A method for producing a bake-hardenable aluminum alloy sheet for forming, which comprises cooling at a cooling rate of 3 ° C./sec or more. 2. Si 0.2-3.0 wt%, Mg 0.2-3.0 wt
%, Cu 0.01 to 1.5 wt%, and aluminum alloy consisting of balance Al and unavoidable impurities, hot-rolled or cold-rolled, then heat-treated at 480 ° C. or higher, and then cold-rolled at 400 ° C. A method for producing a bake-hardenable aluminum alloy sheet for forming, which comprises performing the above solution treatment and cooling at a cooling rate of 3 ° C./sec or more. 3. Si 0.2-3.0 wt%, Mg 0.2-3.0 wt
%, Fe 0.01 to 0.25 wt%, Mn 0.01 to 0.3 wt%
%, Cr 0.01 to 0.5 wt%, Zr 0.01 to 0.5 wt%, Ti0.
An aluminum alloy containing 0.01 to 1.0 wt% of 01 to 0.5 wt% and 0.01 to 0.3 wt% of Ni and 0.01 to 1.0 wt% in total, and the balance Al and unavoidable impurities are hot-rolled or cold-rolled. A bake-hardening aluminum alloy characterized by being heat-treated at 480 ° C or higher, cold-rolled, then solution-treated at 400 ° C or higher, and cooled at a cooling rate of 3 ° C / sec or higher. Method of manufacturing a plate. 4. Si 0.2-3.0 wt%, Mg 0.2-3.0 wt
%, Cu 0.01 to 1.5 wt%, Fe 0.01 to 0.25 wt%,
Furthermore, Mn0.01-0.3wt%, Cr0.01-0.5wt%, Zr0.
01-0.5wt%, Ti0.01-0.5wt%, Ni0.01-0.3wt
% Or more of 0.01% to 1.0% by weight in total, and aluminum alloy consisting of balance Al and unavoidable impurities is subjected to heat treatment at 480 ° C. or higher after hot rolling or cold rolling, and then cold A method for producing a bake-hardenable aluminum alloy sheet for forming, which comprises subjecting a solution treatment to 400 ° C or more after rolling, and cooling at a cooling rate of 3 ° C / sec or more.