| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for producing an Al alloy sheet low in an earing ratio and stably excellent in flanging formability, ironing properties and strength. SOLUTION: At the time of casting an Al-Mg-Mn alloy, thereafter subjecting it to homogenizing treatment and moreover executing hot rolling, the starting temp. is controlled to 350 to 580 deg.C, and, in the stage of 20 to 200 mm sheet thickness in the process of the hot rolling, in the region to a depth of 50μm from the surface, recrystallization is allowed to occur by >=30%. Moreover, from the stage of >=20 mm sheet thickness in the process of the hot rolling to the completion of the hot rolling, the total hot rolling ratio is controlled to <=98%, the rolling temp. in each pass therebetween is controlled to 220 to 450 deg.C, the strain rate in each pass is controlled to 2 to 350/sec, the residence time between each pass is controlled to <=10 min, and the recrystallizing ratio in each pass is controlled to the range of 1 to 80%. Furthermore, the hot rolling finishing temp. is controlled to 200 to 330 deg.C, the finishing sheet thickness is controlled to 1.0 to 7.0 mm, and the average cooling rate of the hot rolled sheet directly after the completion of the hot rolling to a room temp. is controlled to <=100 deg.C/hr to obtain a hot rolled sheet having <=95% recrystallizing ratio at a room temp. and >=70 MPa proof stress. Moreover, after primary cold rolling of 2 to 60%, continuous annealing or batch annealing is executed, and then, final cold rolling of >=50% is executed.
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