Influence of processing route on microstructure and wear resistance of fly ash reinforced AZ31 magnesium matrix composites

Utilizing fly ash (FA) as reinforcement for magnesium matrix composites (MMCs) brings down the production cost and the land pollution. Magnesium alloy AZ31 was reinforced with FA particles (10 vol.%) successfully by two different processing methods namely conventional stir casting and friction stir processing (FSP). The microstructural features were observed using optical microscope, scanning electron microscope and electron backscatter diffraction. The sliding wear behavior was tested using a pin-on-disc wear apparatus. The stir cast composite showed inhomogeneous particle dispersion and coarse grain structure. Some of the FA particles decomposed and reacted with the matrix alloy to produce undesirable compounds. Conversely, FSP composite showed superior particle dispersion and fine, equiaxed grains by dynamic recrystallization. FA particles encountered disintegration but there was no interfacial reaction. FSP composite demonstrated higher strengthening and wear resistance to that of stir cast composite. The morphology of the worn surface and the wear debris were studied in detail.