Macro-alloying Effects of Al and Ag on the Age-Hardening Behavior and Precipitates Microstructure of a Mg-4Sn Alloy

The effects of macro-alloying of Al and Ag on the age-hardening behavior and precipitates microstructure of a Mg-4Sn alloy aged at 160°C were investigated. All the alloys exhibited a similar hardening trend, and achieved the peak-aged state around 230 h. The peak-aged Mg-4Sn alloy contained several thin basal plates and a few Mg2Sn laths heterogeneously distributed within the matrix, which resulted in a poor hardening response. The Mg-4Sn-4Al alloy exhibited an improved age-hardening response by the enhanced precipitation process and an increased volume fraction of the Mg2Sn precipitates. An addition of 1.5 wt.% Ag to the ternary alloy significantly refined the Mg2Sn precipitates. In the peak-aged Mg-4Sn-4Al-1.5Ag alloy, Al and Ag solute atoms still supersaturated the α-Mg matrix, thus further improving the hardness by the solid-solution strengthening effect. Some Ag atoms segregated with the Mg2Sn precipitates, and minor Ag-enriched particles were also formed. In contrast, Al distributed more uniformly in the matrix.