The
microstructures of cast and die-cast magnesium alloys were compared.The microsturcture and mechanical properties of AZ91D die-cast
magnesium alloy after
isothermal heat-treatment were studied.The die cast
alloy was isothermally heat-treated at 300℃ for different time,and then its
microstructure and mechnical properties were investigated by scanning electron microscopy(SEM),X-ray diffraction(XRD),and tensile tests.The results show that the microstructures of cast and die cast samples mainly consist of α-Mg
phase and β-Mg_(17)Al_(12) phase.The β phase is continuously distributed along the boundaries of α-Mg phase and its size is larger in cast alloy than that in die cast sample.During long isothermal heat-treatment of the die cast sample at 300℃ for 60h,the β phase in alloy is coarsening and granulating,and tensile strength(σ_b) and yield strength(σ_(0.2)) of the alloy increase firstly and then decrease slightly because of the solution strengthening effect of β phase.However,the elastic modulus(E) is continuous growing.In addition,the discontinuous distribution of β phase caused by the granulation results in the decrease of elongation(δ) and micro-hardness(HV).
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