Improving mechanical properties of age-hardenable Mg-6Zn-4Al-1Sn alloy processed by double-aging treatment

Microstructure and mechanical properties of a new high-strength Mg-6Zn-4Al-1Sn alloy were investigated. Microstructure of the as-cast Mg alloy exhibited partially divorced characteristics. The dendritic structure of the Mg-6Zn-4Al alloy was significantly refined with the addition of 1% (in weight) Sn, but Mg2Sn phases were not formed. In addition, an icosahedral quasi-crystal phase was formed in the as-cast Mg-6Zn-4Al-1Sn alloy. It was found that after the double-aging treatment through two different heat treatments on the Mg-6Zn-4Al-1Sn alloy, the precipitates were finer and far more densely dispersed in the matrix compared with single-aged counterpart, resulting in a significant improvement in tensile strength with yield strength, ultimate tensile strength and elongation of 175 MPa, 335 MPa and 11%, respectively.