High-strength extruded magnesium alloys: A critical review

Abstract

Magnesium (Mg) has great potential for application in the automotive and aerospace sectors due to its abundant resources and low density. However, the industrial applications of Mg alloys are far below aluminum alloys. At present, most commercial Mg alloys exhibit a low yield strength of < 300 MPa, and their specific strength does not exhibit an advantage over that of aluminum alloys and high-strength steels. Improving the strength of Mg alloys is one of the key topics in this field. In the past two decades, high-strength Mg alloys made by powder metallurgy and severe plastic deformation techniques have been reported, but the small sample dimension and high-cost limit their industrial production. Extrusion can be used to fabricate bulk materials with fine-grained microstructures and improved mechanical properties, which is considered as a suitable route of producing high-strength Mg alloys at the industrial level. In this review, recent advances in the extrusion of different Mg alloys are briefly summarized, including commercial Mg alloys, high-alloyed Mg-RE alloys, and Ca-containing Mg alloys. Different strengthening strategies, including alloying, grain refinement, texture modification, etc., are employed in developing high-strength Mg alloys, with special attention to a novel strengthening mechanism, namely hetero-deformation-induced strengthening, which has recently been applied to simultaneously improve the strength and ductility of Mg alloys. Therefore, the heterostructured Mg alloys prepared by extrusion are also introduced in this work, and the influences of alloying elements and extrusion parameters on the preparation of heterostructured Mg alloys are discussed systematically. Furthermore, this review summarizes the effect of post-extrusion treatment on the mechanical properties of extruded Mg alloys, along with a brief comparison of the mechanical properties between Mg and Al alloys. Finally, some potential research directions for further advancing the high-performance and low-cost extruded Mg alloys are suggested.