Innovative rheocasting processes in Mg foundry

In the present work, the effects of different microstructural features on the mechanical properties of a traditional 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. The results show that the microstructure of traditionally gravity cast step castings consist of primary α-Mg dendrites, while those cast at semi-solid state show the presence of quasi-globular α-Mg phase. Partially divorced α-Mg/β-Mg17Al12 eutectic and fine intermetallic Al-Mn compounds, distributed among the interdendritic regions and along grain boundaries, are also revealed. Due to low solidification rate, discontinuous precipitations of Mg17Al12 into α-Mg grains take also place. The few micrometers size range of α-Mg grains, and the blocky morphology of α/β eutectic and Al-Mn compounds increase the mechanical properties of semi-solid alloy. Furthermore, lower fraction of α/β eutectic in the semi-solid castings tend to increase the mechanical properties.