Microstructure And Mechanical Properties Of Die Casting Mg-Al-Nd Magnesium Alloys And Computer Simulation On Die Casting Processes

Magnesium alloys are the lightest structure materials for various application alloys, due to their low density, high specific strength, high specific stiffness, excellent heat conduction and electric conduction, good dimension stability and easy recovery. However, The use of magnesium alloys has been limited due to poor mechanical properties. So increasing mechanical properties of magnesium alloys is a key problem. Microstructure, tensile properties and low-cycle fatigue properties of as-cast and die-cast Mg-Al-Nd magnesium alloys were studied, in order to establish necessary theory foundation and provide reliable theory evidence for developing and applying magnesium alloys. Meantime, numerical simulation of die casting mold filling process for magnesium alloy die castings were studied, optimizing technological parameters of die-casting.Results show that the microstructure of as-cast and die-cast Mg-Al-Nd magnesium alloys can be refined for the addition of rare earth element Nd, the as-cast alloy with addition of 1% Nd was refined obviously, while the die-cast alloy with the addition of 0.5% Nd is refined obviously. The mechanical properties at room temperature of as-cast Mg-Al-Nd magnesium alloy is the highest with 1% rare earth element Nd, while with the addition of 0.5% Nd, the mechanical properties at room temperature of die-cast Mg-Al-Nd magnesium alloy is the highest. Under different imposed total strain amplitude, die-cast Mg-Al-Nd magnesium alloys exhibite obviously cyclic strain hardening during fatigue deformation, when the imposed total strain amplitudes are 0.3%,0.45% and 1.2%, Mg-8%Al-0.5%Nd magnesium alloys exhibite the longest fatigue life, when the imposed total strain amplitudes are 0.6%,0.8% and 1.0%, Mg-8%Al-1.0%Nd magnesium alloys exhibite the longest fatigue life. On the condition of low-cycle fatigue loading, fatigue cracks initiate transgranularly at casting defect which at the surface of fatigue samples, and propagate in a transgranular mode. Mold filling and solidification processes of magnesium alloy engine hood can be reproduced accurately by computer simulation technology, the optimal parameters are gained according to orthogonal test:injection velocity with 6m/s, die-cast mould temperature with 220℃and pouring temperature with 700℃. Structure of engine hood produced by die-cast is dense, fine grain size. Fractograph is mixture of ductile rupture and cleavage fracture. Mechanical property is that ab=241-244 MPa,σs=179～185 MPa,δ=5.5-6.7%.