Magnesium alloys are known as attractive materials because of their low density and good thermal conductivity. However, compared to their competing metallic materials like aluminum alloys, the strength of magnesium alloys is low. Among different methods introduced for the strengthening of metallic materials, processing by severe plastic deformation is an outstanding method because of its efficiency and relative simplicity. The present study aims to investigate the effect of bismuth content on the microstructure evolution and the hardness of magnesium AZ31 alloy subjected to severe plastic deformation through equal channel angular pressing. For this purpose, different AZ31 alloys containing nominal bismuth contents of 0, 1%, and 3% are processed by up to four passes of equal channel angular pressing at 300 °C. Afterwards, microstructure evolutions of these alloys are observed using the optical and the scanning electron microscopes. The hardness of specimens is measured using the Vickers method. Results show that the bismuth-enriched second-phase particles are fragmented through the severe plastic deformation. Also, increasing of the bismuth content causes more rapid grain refinement through the severe plastic deformation because of the pining effect of these second-phase particles on the grain boundaries. More rapid rates of the hardening through severe plastic deformation are observed for the bismuth-containing AZ31 alloys. This effect is attributed to the more rapid grain refinement and increase of the Hall-Petch coefficient due to the presence of fine bismuth-enriched particles.

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