The effects of different microstructural features on the mechanical properties of a conventional and semi-solid gravity sand cast AM60B alloy are investigated. The Rapid Slurry Forming (RSFTM) technology and a step casting geometry, with a range of thickness from 5 to 20 mm, have been used. Tensile specimens have been drawn from the middle and external regions of the casting. The results show that the microstructure of conventionally gravity cast step castings consist of primary α-Mg dendrites, while those cast from the semi-solid state show the presence of globular and rosette-like α-Mg phase. Partially divorced Mg-Mg17Al12 eutectic and fine intermetallic AlxMny compounds, distributed among the interdendritic channels and along grain boundaries, are also revealed. Due to low solidification rate, discontinuous precipitation of Mg17Al12 also takes place. The presence of primary blocky α-Mg phase and lower eutectic fraction tend to increase the mechanical properties of semi-solid cast Mg alloy.
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