Microstructure and Performance of Four Casting Processes for Magnesium Alloy AZ91

Abstract

The performance of four different casting processes for magnesium alloy AZ91 were evaluated through microstructure characterization, mechanical testing, and SEM analysis of fracture surfaces. Passenger car control arms were cast by indirect squeeze cast, low pressure permanent mold (LPPM), T-Mag, and ablation processes. Samples were cut from twelve locations of the control arms for microstructure characterization. The microstructure, grain size, porosity distribution, and defect analyses were performed using optical microscopy and an image analyzer. Five different defects including microporosity, oxide film, sponge shrinkage, gas pore, and a crack-like defect were identified. The mechanical behavior was characterized using four-point bending (FPB) and tensile tests. The four casting processes were evaluated in terms of reliability using two-parameter Weibull statistics of the ultimate bending strength (UBS) determined from the FPB test samples. Metallographic analyses were performed on these samples, revealing noticeable microstructural differences between them, with some showing possible evidence of oxide films.