Abstract: Effect of Mg content on the microstructure and mechanical properties of Al-Zn-Mg alloy and the effect of aging treatment after cold rolling on the strain hardening were studied by analysis of the as-cast and as-rolled microstructure and mechanical properties of Al-6.0Zn-xMg (x=2, 3, 4) alloys undergone different deformation+heat treatments with XRF, SEM, OM and universal tensile testing machine. The results show that the Mg content has only little effect on the morphology, grain size and second phase type in as-cast state, where the amount of non-equilibrium eutectic phase T-AlZnMg increases with increasing Mg content. When the Mg content is 4%, the amount of eutectic phase decreases, which is related to the increase of MgZn₂ disperse phase near the grain boundaries. After homogenization treatment, hot rolling and cold rolling processing, the high melting point Al₃Fe phase is broken and distributed along the rolling direction. The microstructure transforms as following: as-cast microstructure→fiber microstructure→recrystallized microstructure→fiber microstructure. With the increase of Mg content, the strengths of the as-rolled Al-6.0Zn-xMg alloys increase, but the increments decrease. Aging treatment after cold rolling results in an 80-100 MPa decrease of the strength, and 6%-8% increase of the elongation. Among the three alloys, the Al-6.0Zn-4Mg alloy shows the best comprehensive properties.

Key words: Al-6.0Zn-xMg alloy, Mg content, microstructure, mechanical properties