Influence of Sn and Al contents on the microstructure evolution and mechanical performance of stir-cast Mg-3.0Al-0.5Si alloy

Abstract

Mg-Al-Si alloys are designed for creep resistance, but high Si and Al contents lead to coarse Mg2Si phases and brittle eutectic structures, compromising mechanical performance at elevated temperatures. While research often targets alloys with Si >= 1.0 wt.%, low-Si, low-Al alloys with Sn additions are critical for enhancing mechanical properties. This study examines the microstructure, compressive strength, and creep behavior of a Mg-3.0Al-0.5Si alloy modified with 1.0 and 2.0 wt.% Sn, produced via stir casting, and compares its performance to a Mg-2.0Al-0.5Si-2.0Sn alloy to assess the influence of Al content. The addition of Sn significantly refined grain size and altered precipitate morphology, reducing the size and volume of Mg17Al12 and Mg2Si phases, while Mg2Si phases adopted smaller polyhedral forms. Mg-3.0Al-0.5Si-xSn alloys display improved microhardness, compressive yield strength (CYS), ultimate compressive strength (UCS), total strain to fracture (TSF), and work of fracture (WOF) at 298 and 473 K. Among the alloys, the Mg-2.0Al-0.5Si-2.0Sn alloy has the highest microhardness, CYS, UCS, TSF, WOF, and strain hardening response in the operating temperatures. The impression creep resistance of Mg-3.0Al-0.5Si alloy considerably improved following Sn addition and further proliferated with the reduction of Al content in Mg-2.0Al-0.5Si-2.0Sn alloy. The creep response was mostly governed by pipe diffusion-driven dislocation creep. The Mg-2.0Al-0.5Si-2.0Sn presented the maximum strength and creep resistance, while the Mg-3.0Al-0.5Si-2.0Sn alloy demonstrated best ductility and optimum strength and creep resistance.