The influence of calcium and cerium mischmetal on the microstructural evolution of Mg-3Al-1Zn during extrusion and resulting mechanical properties

The role of calcium and rare earth elements containing particles in magnesium alloys during extrusion in the temperature range T = 250-350 degrees C is studied by optical metallography and texture measurements. A reduction of the final grain size after extrusion, mainly caused by the influence of intermetallic particles is observed, which becomes more distinct for higher alloying contents and low extrusion temperature. The smallest mean grain size (D-mean = 8 mu M) could be observed in a AZ31 + 0.4% Cc mischmetal + 0.8% Ca alloy after extrusion at T= 250 degrees C. The extruded rods exhibit a {1120} + {1010}-fiber texture (c-axes in the radial direction) with a high tension-compression asymmetry of the yield stress in the extrusion direction. The influences of the alloying contents on the texture evolution are discussed in terms of the activation of non-basal slip modes at higher temperatures and the mechanisms of dynamic recrystallization. The textures are distinctly influencing the mechanical properties. The combination of texture and particle hardening is leading to improved strength of calcium-containing alloys. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.