Semisolid processing AZ91 magnesium alloy by electromagnetic stirring after near-liquidus isothermal heat treatment

AZ91 magnesium alloy was semisolid processed under experimental conditions designed to yield from 3 to 40% of the primary particles, and the semisolid slurry was produced by electromagnetic stirring after feedstock had been isothermally heat treated at near-liquidus temperature. The thixotropic microstructures obtained were characterized in detail and linked to the corresponding tensile properties. A unique microstructure was exhibited that the primary particles conglutinated together to form clusters due to sliding between solid particles and plastic deformation of solid particles during semisolid deformation [C.P. Chen, C.-Y.A. Tsao, Acta Mater. 45 (5) (1997) 1955-1968] which resulted from electromagnetic stirring. An increase of solid fraction exacerbated this agglomerating phenomenon accompanying an increment of β-Mg17Al12 content, and those finally resulted in a reduction in elongation. The fractographic analysis revealed that fracture mechanism and corresponding morphology of the rapture surface of tensile bars depend on the solid fraction of the primary particles.