The Mechanical Property and Microstructure of Extruded Mg-8Sn-4Al Alloy with Different Extrusion and Heat Treatments

The process optimization of extrusion, solution, and aging treatment was investigated to improve the microstructure and mechanical property of extruded Mg-8Sn-4Al-1Ag-0.8Sc alloy. The microstructure was characterized by X-ray diffraction (XRD), electron backscattered diffraction (EBSD), and transmission electron microscopy (TEM), and tensile tests were used to measure corresponding mechanical property. The solution–extrusion-treated (SE), solution–extrusion–aging-treated (SEA), and solution–ageing–extrusion-treated (SAE) alloys were mainly studied. The SAE alloy exhibited a noticeable tensile strength with a relatively good elongation of 359.86 MPa and 18.08%, respectively. This is mainly attributed to a smaller average grain size (~ 1.86 μm), which is due to a more thorough dynamic recrystallization behavior induced by aged precipitates. Interestingly, the Mg₂Sn precipitates enriched in Sn, Ag, and Sc elements were observed in both the SEA and SAE alloys. The Mg₂Sn precipitates morphology of the SEA alloy is mainly blocky and ellipsoidal. However, the Mg₂Sn precipitates morphology of SAE alloy is mainly spherical or ellipsoid with a smaller precipitates size. The different shapes and sizes of Mg₂Sn precipitates from the SAE and SEA alloys also slightly contributed to their different mechanical properties and corresponding mechanism was discussed in detail.