JPH05279822A - Production of aluminum alloy material for forming excellent in hardenability of coating/baking, formability, and shape freezability - Google Patents

Abstract

PURPOSE:To produce an aluminum alloy material for forming suitable for producing automobile outer sheet, transport equipment, etc., and excellent in formability at the time of press working, shape freezability, and baking hardenability. CONSTITUTION:An alloy having a composition consisting of, by weight, 0.4-1.5% Si, 0.3-1.5% Mg, and the balance Al is subjected to semicontinuous casting. The resulting ingot is subjected to ordinary rolling, to solution heattreatment, to hardening, and to air cooling at room temp. The resulting stock is subjected to pre-heat treatment within a day at 15-120 deg.C for >=1hr and then to final heat treatment at 200-300 deg.C for <1min. By this method, the aluminum alloy material for forming excellent in hardenability of coating/baking, formability, and shape freezability can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an aluminum for forming, which is particularly suitable for the production of transportation equipment such as outer plates for automobiles and which is excellent in formability during press working, shape fixability and paint bake hardenability. The present invention relates to a method for manufacturing an alloy material.

[0002]

2. Description of the Related Art Conventionally, various aluminum alloy materials have been developed and used as materials for transportation equipment such as outer panels for automobiles.

For example, the required performance of an outer panel for automobiles is 1) formability, 2) shape freezeability (the shape of the press die is accurately produced during press working), 3) high strength, and 4) resistance. Dent property, 5) Corrosion resistance, etc.

Among the required performances, the formability is evaluated by elongation, Erichsen value, etc., and the shape fixability becomes better as the longitudinal elastic modulus becomes larger and the proof stress becomes smaller. Further, the dent resistance becomes better as the yield strength and the plate thickness increase.

In order to solve this contradiction, the proof stress before the press working is low, the shape fixability is improved, and after the press working, it is hardened in the coating baking process at 175 ° C. for about 30 minutes, so that the proof stress is remarkably increased. If so, the dent resistance becomes good and all the problems are solved. However, the existing alloy produced by the conventional method could not satisfy both the excellent shape fixability during press working and the dent resistance and structural strength after press working.

For the above problem (Japanese Patent Application No. 3-1243)
In 1), a method for producing a material excellent in paint bake hardenability was described, but the final heat treatment was as long as 1 minute or more, which was not desirable in industrial production using a continuous heat treatment furnace.

[0007]

Therefore, in the present invention, a detailed examination of the chemical composition and the thermomechanical treatment step will result in
It is intended to provide an aluminum alloy for molding, which can shorten the final heat treatment time and which does not deteriorate the performance and is excellent in paint bake hardenability, formability, and shape fixability.

[0008]

The constitution of the present invention for solving the above-mentioned problems is a method for producing an aluminum alloy material for forming as described in the claims.

Each condition will be specifically described below.

Si: Required for obtaining high strength, Mg ₂
High strength can be obtained by forming Si. If it is less than 0.4%, the strength is low and sufficient strength cannot be obtained even if the coating is heated by baking. On the other hand, if it exceeds 1.5%, the yield strength after the final heat treatment is high, and the moldability and shape fixability are poor.

Like Mg: Si, it is necessary to obtain high strength, and if it is less than 0.3%, the strength is low and sufficient strength cannot be obtained by heating during baking of the coating. On the other hand, if it exceeds 1.5%, the yield strength after the final heat treatment is high and the formability and shape fixability are poor.

Cu: The strength can be further increased by adding Cu. However, if added in excess of 1.0%, the yield strength after completion of the final heat treatment is high, the formability and shape fixability are poor, and the corrosion resistance is poor.

Mn: By adding Mn, the strength can be further increased, and the crystal grains can be made finer.
Moldability is improved. However, if added in excess of 0.5%, the yield strength after completion of the final heat treatment is high, the formability and shape fixability are poor, and the coarse intermetallic compounds increase, so the formability decreases.

Cr: By adding Cr, the strength can be further increased, the crystal grains can be made finer, and the formability can be improved. However, if it is added in an amount of more than 0.2%, the yield strength after completion of the final heat treatment is high, the formability and the shape fixability are poor, and coarse intermetallic compounds increase, so that the formability decreases.

V: By adding, the strength can be further increased, the anisotropy of mechanical properties can be reduced, the crystal grains can be made finer, and the formability can be improved. However, if added over 0.2%, the yield strength after completion of the final heat treatment is high and the formability and shape fixability are poor.

By adding Ti, the cast structure can be made finer and ingot cracking can be prevented. But 0.05
If it is added in excess of%, coarse intermetallic compounds increase, resulting in deterioration of moldability.

B: By adding together with Ti, the cast structure can be made finer and ingot cracking can be prevented. However, if it is added in excess of 100 ppm, the amount of coarse intermetallic compounds increases, and the formability decreases.

Room temperature storage time When the room temperature is lower than 15 ° C .: If the material is not preheated within 1 day of storage at room temperature, GP zones are sufficiently formed due to room temperature aging, and GP zones formed below 15 ° C. are extremely It is stable and requires a lot of decomposition energy. Therefore, in order to lead to dispersion and deterioration of performance in the subsequent heat treatment, preheat treatment is performed within 1 day and the temperature is kept at 15 ° C or higher. If it is left at room temperature for more than 1 day, the final heat treatment will take a long time, which is industrially undesirable.

When the room temperature is 15 ° C. or higher: The performance can be obtained even if the material is left at room temperature as it is quenched, but if the temperature is maintained at a higher temperature, the final heat treatment provides a higher performance in a shorter time.

Pre-heat treatment after being left at room temperature: By maintaining the temperature at 15 ° C. or higher and 120 ° C. or lower for 1 hour or more within 1 day of standing at room temperature, formation and stabilization of a GP zone that easily decomposes can be achieved.

Sufficient performance can be obtained by controlling the time of the final heat treatment even at 15 to 30 ° C., but it is desirable to maintain the temperature at 35 ° C. or higher in order to further shorten the final heat treatment.

As a result, the room temperature age hardening in the final heat treatment is suppressed to maintain good formability, and the coating baking
When heated to about 75 ° C., it easily hardens in a short time.
At room temperature, a GP zone that is difficult to decompose is formed at less than 15 ° C, and the subsequent heat treatment does not cause sufficient hardening.
If it exceeds 20 ° C., a metastable phase precipitates and the final yield strength increases, so that the formability decreases.

There is no problem even if the pre-heat treatment time is long.

Final heat treatment after pre-heat treatment: 2 after pre-heat treatment
The GP zone is decomposed by performing a restoration treatment for 1 minute or less at a temperature of 00 ° C or more and 300 ° C or less, and then the room temperature age hardening is suppressed to maintain good formability, and when the coating is heated to about 175 ° C. Easy to cure in a short time.

If the temperature is less than 200 ° C., it is not sufficient for decomposition of the GP zone, and the coating bake hardenability deteriorates.
Above 0 ° C, the yield strength increases due to the precipitation of metastable phases,
Further, since the elongation is lowered, the formability is poor and the paint bake hardenability is also lowered.

There is no time limit at room temperature from the end of the preheat treatment to the start of the final heat treatment.

[0027]

[Examples] After semi-continuous casting of the alloys shown in Table 1, the surface of the casting surface was cut. Fe is an impurity. Then 500 ° C
After homogenizing for 24 hours, start hot rolling to obtain a thickness of 6
Rolled to mm. And after cold rolling, thickness 1mm
It was a plate. Further, in the continuous annealing furnace, the heating rate is 500
Perform solution treatment at 530 ° C for 60 s at 10 ° C / min for 10
It was cooled to 0 ° C. at 500 ° C./min, and subjected to room temperature standing time-pre-heat treatment-final heat treatment under the conditions shown in Table 2. The mechanical properties of these materials were evaluated after aging for 1 month at room temperature after the final heat treatment.

Table 3 shows the evaluation results of the test materials. The judgment is
Those with a yield strength after room temperature aging for 1 month of 130 MPa or less are excellent shape fixability, and those with an elongation of 28% or more and an Erichsen value of 9.5 mm or more have good moldability,
And the increase in yield strength after heating to 175 ° C for 30 minutes is 50M
A material having Pa or more was considered to have good paint bake hardenability, and a material having a proof stress after paint bake hardening of 135 MPa or more was regarded as a material having good dent property, and was passed.

All of Examples 1 to 12 of the present invention are within the scope of the claims and good performances are obtained.

In Comparative Example 13, the amount of Si was smaller and in Comparative Example 14, the amount of Mg was smaller than the lower limit of the claimed range, so that the coating bake hardenability was poor and the yield strength was low even in the heat treatment at 175 ° C. for 30 minutes. ..

Comparative Example 15 has a Si content, and Comparative Example 16 has a Mg content.
In Comparative Example 17, since the Cu content was larger than the upper limit of the claimed range, the yield strength exceeded 135 MPa, the shape fixability was poor, and the moldability was poor.

Comparative Example 18 has a Mn content, and Comparative Example 19 has a Cr content.
In Comparative Example 20, the amount of V was larger, the amount of Ti in Comparative Example 21 was larger than the amount of Ti in Comparative Example 22, and the amount B was larger than the upper limit of the claimed range, so the elongation was small and the formability was poor.

In Comparative Examples 23 and 24, the pre-heat treatment temperature was lower than the lower limit of the claims, so that the coating bake hardenability was poor.

In Comparative Example 25, the preheat treatment temperature was higher than the upper limit of the claimed range, so that the yield strength exceeded 135 MPs, the shape fixability was poor, and the moldability was poor.

In Comparative Example 26, the final heat treatment temperature was lower than the lower limit of the claimed range, and thus the coating bake hardenability was poor.

In Comparative Example 27, since the final heat treatment temperature was higher than the upper limit of the claimed range, the yield strength was increased, the shape fixability was poor, and the paint bake hardenability was low. In Comparative Example 28, the coating bake hardenability was inferior because the room temperature standing time was longer than the upper limit of the claims.

[0037]

[Table 1]

[0038]

[Table 2]

[0039]

[Table 3]

[0040]

[Table 4]

[0041]

EFFECTS OF THE INVENTION By using the present invention, various kinds of thin plate molding materials can be manufactured in a short time using conventional equipment, and further weight reduction can be promoted. Further, although the present invention has been mainly described with respect to the plate material, it can be applied to other manufacturing methods such as an extruded material because the principle of alloy material manufacturing is the same.

Further, even if the coating baking temperature is lowered to 150 ° C. or lower in the near future, curing as high as 175 ° C. cannot be expected, but when the method of the present invention is used, it is clearly better than the conventional method. Excellent performance can be obtained.

Alternatively, when heated at 200 ° C., which is similar to that in Europe and America, a sufficient amount of curing can be expected in a shorter time than conventional materials.

Claims (2)

[Claims] 1. A weight-based alloy containing Si: 0.4% or more and 1.5% or less, Mg: 0.3% or more and 1.5% or less, and the balance being Al semi-continuously cast, The obtained ingot is subjected to normal rolling, solution treatment, quenching, and left at room temperature, and preheated at a temperature of 15 ° C. or higher and 120 ° C. or lower for 1 hour or longer, and then 200 ° C. A method for producing an aluminum alloy material for forming, which is excellent in paint bake hardenability, formability, and shape fixability, characterized by performing a final heat treatment for 1 minute or less at a temperature of 300 ° C. or less. 2. On a weight basis, Si: 0.4% or more and 1.5% or less, Mg: 0.3% or more and 1.5% or less, and further Cu: 1.0% or less and Mn. : 0.5% or less Cr: 0.2% or less V: 0.2% or less Ti: 0.05% or less B: 100 ppm or less One kind is contained, and the balance is obtained by semi-continuously casting an alloy consisting of Al. After subjecting the obtained ingot to ordinary rolling, solution treatment, quenching, and leaving at room temperature, the material is preheat-treated at a temperature of 15 ° C or higher and 120 ° C or lower for 1 hour or longer, and then 200 ° C or higher. A method for producing an aluminum alloy material for forming, which is excellent in paint bake hardenability, formability, and shape fixability, characterized by performing a final heat treatment for less than 1 minute at a temperature of 300 ° C. or less.