Effects of Mechanical Vibration and Wall Thickness on Microstructure and Mechanical Properties of AZ91D Magnesium Alloy Processed by Expendable Pattern Shell Casting

Abstract

Mechanical vibration was introduced into the solidification process of AZ91D magnesium alloy during the expendable pattern shell casting process, and the combined effects of mechanical vibration and wall thickness on the microstructure and mechanical properties were investigated. The results indicate that with the increase of wall thickness, the morphologies in α-Mg phase and β-Mg₁₇Al₁₂ phase of the samples obtained without vibration evolved from a fine dendrite to a coarse dendrite and from a fine continuous network structure to a coarse continuous network structure, respectively, and the mechanical properties and density of AZ91D alloy continuously decreased. With the application of mechanical vibration, the coarser dendrites transformed into fine equiaxed grains, and the previous coarse continuous network structure of the β-Mg₁₇Al₁₂ phase was changed to a discontinuous granular morphology. Meanwhile, the mechanical properties and density of AZ91D alloy greatly increased. The effect of mechanical vibration on the microstructure and mechanical properties increased with increasing vibration frequency and wall thickness. The fractographs of the tensile samples show a change in fracture surface from brittle to that of a tough fracture with the addition of vibration.