Hot extrudability of Mg-Al-Zn based alloy cutting chips and surface properties of extrusions

Hot extrusion tests for the purpose of recycling of cutting chips were carried out for AZ31B and AZ91D magnesium alloys. The tensile properties at room temperature and the surface quality of the extrusions were evaluated. Excellent mechanical properties at room temperature were obtained for an extrusion temperature of 423 K for AZ31B and for 573 K for AZ91D alloy, respectively. The tensile strength and yield strength of AZ31B cutting chip extrusion were higher than those of the extrusion from AZ31B cast billet, probably due to a grain refinement effect. However, the peculiar and wavy surface roughness almost perpendicular to the extrusion direction was formed in the extrusions from cast billet as well as in the extrusions from cutting chips of both alloys. On the extrusion surface of AZ31B alloy cutting chips, a mixed texture of basal and non-basal planes was formed. Moreover, a strong basal plane texture was observed in the layer approximately 0.4 mm from the surface. Discontinuous metal flow due to the difficulty of basal plane slip along the die exit corner with a sharp rectangular edge appeared to form the peculiar and wavy surface roughness.