Achieving extremely high speed extrusion and medium strength in a Mg–Bi–Si ternary alloy

Abstract

In this work, we report a new Mg–5Bi–1Si (wt.%) alloy showing a synergy of extrusion speed (ES) and tensile yield strength (TYS). At high ESs, it still has a good alloy surface, owing to the formation of thermally stable Mg3Bi2 and Mg2Si phases and the disappearance of small-sized low-melting divorced eutectic Mg3Bi2 phases for the as-cast alloy. During 70 m/min extrusion, the fragmentation of pre-existing eutectic (Mg3Bi2 and Mg2Si) phases and the dynamic precipitation of new (Mg3Bi2) phases impede the excessive grain coarsening and provide the effective strengthening contributions on the TYS of ∼253 MPa. After T5 peak aging, two types of basal Mg3Bi2 precipitates are found and further enhance the TYS to ∼280 MPa.