Observations of intermetallic particle and inclusion distributions in magnesium alloys

As part of an international program to qualify magnesium alloy ingots as feed stock for die-castings, numerous studies have been conducted on the microstructures of AM50, AM60, and AZ91 virgin and recycled ingots. The studies have focused on intermetallic particles and inclusions distributed throughout the ingot bulk, and concentrated in surface defect regions such as folds. The studies have included optical macrography and micrography to document the particle distributions, automated optical image analysis for quantifying the particle volume fraction and size, and scanning electron microscopy and energy dispersive spectroscopy to characterize the elemental content of the particles and surrounding matrix. Several example case studies are presented in this paper.