Microstructural evolution and tensile mechanical properties of AM60B magnesium alloy prepared by the SIMA route

Cyclic closed-die forging (CCDF) was introduced into the strain induced melt activation (SIMA) route to replace conventional upset or extrusion. The microstructure evolution of CCDF formed AM60B magnesium alloy heated into the semi-solid state has been investigated. Tensile mechanical properties for AM60B magnesium alloy thixoformed from starting material produced by the SIMA route were determined. The results show that the SIMA route (four-pass CCDF and partial remelting) produced ideal, fine semi-solid microstructure, in which completely spheroidal primary solid grains had a little amount of entrapped liquid. With increasing the equivalent strain, the solid grain size decreased and the degree of spheroidization tended to be improved. Furthermore, the rate of liquation was also slightly increased. Increasing the reheating temperature was favorable for obtaining spheroidal semi-solid microstructure and decreasing the probability of coalescence among solid grains. However, prolonging holding time resulted in grain coarsening. The tensile mechanical properties of the thixoformed components were influenced by the amount of equivalent strain during CCDF. Good elongation to fracture (15%) was obtained for thixoformed AM60B magnesium alloy component, with a yield strength of 199.2 MPa and a tensile strength of 306.7 MPa.