Influence of Microstructure on the Mechanical Properties of Thixomolded® Magnesium Alloys

Abstract

Abstract Thixomolding® processes of magnesium have been highlighted in research and applications in the last decade. While in the past its use was mainly driven by consumer goods and electronic applications by Asian manufacturers (such as notebook computer cases, digital camera bodies, chain saw housings, etc.), currently Thixomolding® has been widely extended to other applications. Some examples are in automotive and sports equipment, such as automotive shift cams, bicycle saddles, fishing reels, snowboard bindings, etc. Wider applications of Thixomolding® magnesium alloys mainly depend on various advantages such as a simple and completely automatic manufacturing process, high productivity, and repeatability of the mechanical properties of parts. Moreover, due to low molding temperatures and laminar flow of the semisolid injected material, longer die life and dimensional precision are expected. In addition, complex geometry and net shape forming are possible, thus avoiding any further machining. Finally, residual porosity, which is one of the typical defects of cast parts (due to gas entrapment in turbulent flow), is avoided because of the laminar flow injection molding in tool-die. In this work, the thixomolded AZ91D and AM60B alloys have been investigated. A complete analysis has been conducted on the as-supplied material, by investigating the microstructure, tensile properties and axial fatigue (fatigue ratio R=0.1) performance. To improve mechanical characteristics, the Tx heat treatment has been performed on the thixomolded material and its effect on the microstructure has been analyzed and documented as a partial dissolution of brittle β-Mg17Al12 phase. The effect of heat treatment on mechanical properties of the material has been investigated and documented including the evaluation of a toughness index.