Microstructure and Mechanical Behavior of Cast Mg AZ31B Alloy Produced by the Magnetic Suspension Melting Process

Magnesium is the lightest of all structural metals and offers significant weight savings compared to traditional automotive materials. This paper describes the macrostructure and the microstructure of Mg AZ31B alloy produced via the Magnetic Suspension Melting (MSM) technique at a low superheat of 5 degrees C. It was found that casting at this low superheat produced a fine globular grain structure in comparison to a dendritic structure in conventionally cast alloys. The intermetallic phases were analyzed in detail and compared with the conventionally cast alloy. In the MSM cast alloy, the Mg17Al12 phase formed mainly at the grain boundaries, in contrast to typical dendritic entrapment of this phase within the grains in conventional castings. The formation of the Al-rich secondary-alpha phase during solidification was investigated. The effects of this morphology change on mechanical and fracture behavior of this material are presented. These results are discussed relative to conventionally cast Mg alloys.