Age Hardening Behavior and Mechanical Properties of Al-11%Zn-3%Mg-1.4%Cu (-0.2%Ag) Alloys

Aging behavior, cluster formation including near grain boundaries, and mechanical properties of Al-11%Zn-3%Mg-1.4%Cu (-0.2%Ag) alloy were investigated. The effect of Ag as a microalloying element was also clarified. The Al-11%Zn-3%Mg-1.4%Cu (-0.2%Ag) alloy showed higher aging hardening ability and shorter time to peak aging than the Al-5%Zn-2%Mg (-0.3%Ag) alloy from the early aging stage. The effect was greater with the addition of Ag, showing that the effects of solute content and micro-alloying elements on age hardening were recognized. 3DAP analysis revealed that Ag contributed significantly to the initial stage of cluster formation even when the solute elements were high. It was also found that clustering occurred in the vicinity of the grain boundary at a high density and fineness from the early stage of aging. By increasing the solute content of Zn and Mg to 11% and 3% respectively, the tensile strength of the alloy was over 800 MPa, and the addition of Ag further increased the strength.