Correlation between microstructure and tensile properties in powder metallurgy AZ91 alloys

The ultrafine-grained (0.3-1.3 mu m) AZ91 alloys, which were fabricated by powder extrusion in the range of 200 to 350 degrees C and subsequent aging at 100 degrees C for 8 h, exhibit a remarkable yield stress of 360-478 MPa and moderate tensile elongations of 6-8%. A composite structure was developed after extrusion with uniform beta (Mg(17)Al(12)) particles dispersed in magnesium matrix. The extrusion temperature has an indirect role on yield stress since partial dissolution of beta particles induced by high extrusion temperature fails to retard grain growth. Moreover, the strength was further enhanced by the formation of nano-scale precipitates during artificial aging. The high strength could be attributed to a combination effect of grain refinement, particle reinforcement and precipitation hardening. (C) 2011 Elsevier BM. All rights reserved.