JP2004323952A5 - - Google Patents

Description

3. The method for producing an aluminum alloy sheet for forming according to claim 2,
After the stabilization treatment, the mixture is further heated to a temperature in the range of 170 to 280 ° C. at a heating rate of 100 ° C./min or more and maintained at a temperature in the range for 5 minutes or less , and then cooled at a rate of 100 ° C./min or more. A method for producing an aluminum alloy sheet for forming, which is excellent in bending and other formability and bake hardenability and has low elongation and bending anisotropy, characterized by performing a final heat treatment of cooling at a high speed.

The method for producing an aluminum alloy sheet for forming according to the third aspect of the present invention is the method for producing an aluminum alloy sheet for forming according to the second aspect, wherein after the stabilizing treatment, the temperature is further increased to 100 ° C./min or more. After heating to a temperature in the range of 170 to 280 ° C. at a heating rate and maintaining the temperature within the range for 5 minutes or less , a final heat treatment of cooling at a cooling rate of 100 ° C./min or more is performed. It is.

Further, in the present invention, the sum of the lengths of the small-angle grain boundaries in the crystal structure, that is, the sum of the lengths of the grain boundaries having a rotation angle in the range of 5 to 15 °, is the sum of the lengths of all the grain boundaries having a rotation angle of 5 ° or more. It should fall within the range of 2-90% relative to the sum of the length. That is, since the sum of the lengths of the small-angle grain boundaries of 5 ° or more and 15 ° or less is within a certain range with respect to the sum of the lengths of all the grain boundaries of 5 ° or more, the bending along the grain boundaries is performed. The effect of alleviating cracks is obtained. If this ratio is less than 2%, good bendability may not be obtained. On the other hand, if it exceeds 90%, the surface may be roughened at the time of molding and the surface quality of the sheet may be degraded. Therefore, in the present invention, the ratio of the small-angle grain boundaries is specified as described above in order to obtain good bending properties and good sheet surface quality.

After the solution treatment, cooling (quenching) is performed at a cooling rate of 100 ° C / min or more to a temperature range of 50 ° C or more and less than 150 ° C. Here, if the cooling rate after the solution treatment is less than 100 ° C./min, a large amount of Mg ₂ Si or elemental Si precipitates at the grain boundaries during cooling, and the moldability, particularly the hem bending property, decreases, and at the same time, The bake hardenability is reduced, and it is no longer possible to expect a sufficient improvement in the strength during baking.

After performing the stabilization treatment as described above, it may be used as it is as a product plate, and may be subjected to a forming process for an automobile body sheet or the like, but in order to further improve paint baking hardenability and hem bending property. May be further subjected to a final heat treatment. The final heat treatment is heated to equity 5 minutes or less coercive at a heating rate of 100 ° C. or more within a temperature range of 170 to 280 ° C., it is necessary to make the conditions for cooling at 100 ° C. / min or higher cooling rate.