Narrow Results

The solidification microstructure of cast SiC particles reinforced magnesium composite has been studied using optical and transmission electron microscope (TEM). Metallographical examination showed that the grain size of magnesium composite was much smaller than that of unreinforced magnesium alloy. In the mean time most SiC particles were pushed and segregated at the grain boundaries while few SiC particles were entrapped in the magnesium grain. The primary magnesium phase which heterogeneously nucleated on the SiC particle surface has been identified with a small lattice disregistry (2.3%) while their crystallographic orientation relationship was . Finally, the grain refining mechanisms in SiC particles reinforced magnesium composite have been proposed.

The effects of different initial condition (as-cast, homogenized) on grain refinement strengthening of AZ31B magnesium alloy were investigated by optical microscopy and tensile testing. The results show that the inhomogeneous second-phase γ-Mgl7Al12 along the grain boundary in as-cast was still distributed unevenly after extrusion. Compared with as-cast, tensile strength of homogenization was increased greatly after extrusion. At 250°C and extrusion ratio of 50, tensile strength reached to 391Mpa and elongation of 15.2%.The grain size after extrusion is bigger than that of as-cast after extrusion, so the Tensile strength is lower than that of as-cast. Besides, non-equilibrium phase γ-Mgl7Al12 has been dissolution after homogenized and grain distributed uniformly. Therefore, plasticity was improved greatly at the same condition as upon.