Effects of extrusion temperature and extrusion ratio on the microstructure and properties of Mg–5Sn–1Ca alloy prepared by continuous squeeze casting-extrusion process

In this study, a high-strength and high-toughness Mg–5Sn–1Ca (i.e., TX51) alloy was produced through a continuous squeeze casting-extrusion (CSCE) process without billet homogenization or secondary preheating for the first time. Effects of extrusion temperature and extrusion ratio on the microstructure and mechanical properties of extruded TX51 alloy were investigated. The results show that the CaMgSn eutectic in the as-cast billet was crushed during the CSCE process and exerted the particle stimulated nucleation (PSN) effect, which stimulated dynamic recrystallization of α-Mg. Improper extrusion temperature and extrusion ratio will lead to incomplete recrystallization or grain growth in the extruded alloy, whereas the average grain size of CSCE TX51 alloys can be as small as 2 μm under appropriate process parameters. Interestingly, the TX51 alloy prepared by the CSCE process achieved an excellent strength-toughness match, with optimal ultimate tensile strength, yield strength and elongation of 277.1 MPa, 233.2 MPa and 23.27%, at an extrusion ratio of 16:1 and an intermittent time of 60s (i.e., extrusion temperature is 246 °C). Based on quantitative calculations, the high strength and plasticity are attributed to four strengthening mechanisms, among which grain boundary strengthening and geometric strengthening are the most important contributors.