Microstructure and properties of solution treated semi-solid AZ91 magnesium alloy slab which was forged with 60% reduction at 400℃ after extrusion were investigated. The results indicate that fine grain size in extruded AZ81 magnesium alloy can be observed

in which major broken Mg17Al12 phase is dispersedly distributed along grain boundary with minor streamline ones. Yield strength

tensile strength and elongation of the extruded alloy are increased by 69.9%

63.2% and 164.6%

respectively

compared with those of semi-continuous alloy slab. Refiner grain size can be observed in extruded AZ81 magnesium alloy after forged treatment

in which re-broken Mg17Al12 is partly dissolved into grain. The yield strength

tensile strength and elongation of extruded AZ81 magnesium alloy after forged treatment reach 229MPa

337MPa and 15.5%

respectively

increased by 9.6% and by 8.7%

22.3%

respectively

compared with those of extruded ones

greatly improving the mechanical properties. Properties of the AZ81 magnesium alloy are closely related to the refinement of grain and distribution of Mg17Al12 phase. SEM and OM observation show that fracture morphology of extruded-forged AZ81 magnesium alloy is characterized by ductile crack.