Influence of different Mg/Si ratio on recrystallized structure and mechanical properties of Al-Mg-Si alloy containing Zn

Abstract:

In order to improve overall performance of automotive sheet of Al-Mg-Si series alloy, three groups of alloy ingots were prepared by casting method, then, 1 mm thick alloy sheets were achieved through homogenization, hot rolling, intermediate annealing, cold rolling. After solution treatment at 560 ℃ for 30 mins, immediately pre-aging at 100 ℃ for 8 h, and then stored at room temperature for 14 days to simulate the process of transportation and storage. Finally, the alloy sheets baked hardening at 185 ℃ for 20 mins after 2% deformation. The microscopic structure of alloy was observed by metallographic microscope; its texture was analyzed by scanning electron microscope equipped with electron back scattering diffraction, and the mechanical property was tested by electronic universal testing machine. The effect of different Mg/Si ratio and high Zn content on recrystallized structure and texture, bake hardenability and corrosion sensibility were studied. The results indicated that the recrystallized structure of alloy with equal Mg/Si ratio was smaller and more uniform. The average size of grains was 190 μm. The cube orientation {001}<100> was smaller, while the P orientation {011}<122> was larger. Whereas the local grains of alloys with high Mg content and high Si content were coarse, the cube component {001}<100> was larger and the P component {011}<122> was smaller. The strength of alloy with equal Mg/Si ratio was higher, accompanied by good bake hardenability after pre-aging. The paint-bake hardening increment was 107 MPa. After bake hardening, more Zn atoms were diffused into grain boundary, enhancing the response of micro-current. The resistance of corrosion sensibility was poorer than that of high Mg content and high Si content alloy. The depth of corrosion was 121 μm.