Microstructure and Mechanical Properties of a Cold-Rolled Al-6.5Mg-1.5Zn-0.5Fe-0.5Mn System Alloy

The annealing characteristics of cold-rolled Al-6.5Mg-1.5Zn-0.5Fe-0.5Mn alloy, newly designed as an automobile material, are investigated in detail, and compared with those of other aluminum alloys. Using multi-pass rolling at room temperature, the ingot aluminum alloy is cut to a thickness of 4 mm, width of 30 mm, and length of 100 mm to reduce the thickness to 1 mm (r = 75%). Annealing after rolling is performed at various temperatures ranging from 200 to 500 degrees C for 1 hour. The specimens annealed at temperatures up to 300 degrees C show a deformation structure; however, from 350 degrees C they have a recrystallization structure consisting of almost equiaxed grains. The hardness distribution in the thickness direction of the annealed specimens is homogeneous at all annealing temperatures, and their average hardness decreases with increasing annealing temperature. The tensile strength of the as-rolled specimen shows a high value of 496MPa; however, this value decreases with increasing annealing temperature and becomes 338MPa after annealing at 400 degrees C. These mechanical properties of the specimens are compared with those of other aluminum alloys, including commercial 5xxx system alloys.