The Research On The Semi-solid Diecasting Processing Of AZ91D Magnesium Alloys

The task of this study is forming good parts by semi-solid die casting via to optimizing the forming processes. Preparative of the no-dendrite AZ91D magnesium alloy billets by semi-solid isothermal heat treatment.The tradition chamber can not be used in semi-solid diecasting, now, the condition has changed, because the chamber which designed for semi-solid diecasting was used in the experience. The heated chamber which can supply the calories for the liquid alloy and abate the freezing speed. The excellent fluidity of the alloy fit the semi-solid diecasting of magnesium alloy.The influences of filling speed and pressure of diecasting was investigated. The result indicated that the tensile strength and elongation increased with increasing of filling speed or pressure. The tensile strength has the maximal of 237.5MPa and the elongation is 4.8%. After T4 treatment, the tensile strength has increased to 248MPa, elongation is 4.6%, and hardness is 69HBS.The structures of different positions of the casting were observed. Comparing with the isothermal heat treatment, the grain size is smaller after diecasting. The result shows that the plunger forge plays a role on grain refinement. The liquid phase in remelt billets is decrease after shaped and the solid phase has incrased from the location piercer to the location far away from ingate.The fracture morphology of tensile tested specimens has analysed. The result indicated that the fracture morphology of the semi-solid diecasting was along grain boundaries mainly. The structure of diecating specimens is primary α-Mg and β phase. The β phase is frangible, which leads to frangible fracture at the boundaries.