Effects of Mg2Sn precipitation on the age-hardening and deformation behaviour of a Mg-Sn-Al-Zn alloy

The influences of Mg2Sn precipitation on the age-hardening and deformation behaviour of a Mg-4Sn-3Al-1Zn (wt.%) alloy have been systematically investigated via the assistance of analytical electron microscopy and X-Ray Computed Tomography (XCT) techniques. The Mg-4Sn-3Al-1Zn alloy shows a moderate hardening response during the ageing heat treatment at 175 °C, and a ∼35% increment of yield tensile strength was achieved with significantly deteriorated tensile elongation under the peak-aged condition. Nanosized Mg2Sn precipitates are uniformly distributed within grains, improving tensile strength properties. In addition, coarsened Mg2Sn precipitates can be observed along with precipitate-free zones (PFZs) at grain boundaries. During tensile deformation of the solution-treated alloy, plastic strain tends to be localized in the slip band array regions in grain interiors. For the as-aged alloy, strain localization primarily occurred in the PFZs. The degraded tensile ductility was associated with the initiation of early intergranular microcracks caused by coarse grain boundary Mg2Sn precipitates and PFZs. The results provide insights and implications for the development of affordable Mg alloys with a balanced combination of strength and ductility.