Preparation and characterization of aluminum borate whisker reinforced magnesium alloy composites by semi-solid process

To develop a new kind of composite material, 'graded morphology MMCs', a semi-solid magnesium alloy was squeeze-cast into an aluminum borate whisker preform. Currently, to increase the interfacial tensile/shear strength between MMCs and some metal parts, the joining processes have beenstudied. However, a suitable process has not yet been found. In this study, we first studied the optimum manufacturing condition to increase the preform compressive strength which should be necessary to prevent the preform from deformation in the squeeze cast process. The dependence of thebinder types, which were the SiO₂, Al₂O₃, and TiO₂ sols, the binder content (0-5 mass% vs whisker amount), and the sintering temperature (1000- 1 160°C) of the preform were measured. We then examined the microstructure of the obtained materialwhich was in situ joined with the semi-solid magnesium alloy (Mg-9 mass% Al-1 mass% Zn). The results were as follows: (1) The SiO₂ sol was the most effective as a binder to increase the preform compressive strength. (2) During the squeeze cast process, the particles of the α-Mgsolid phase in the semi-solid alloy were filtered by the preform and piled up in front of the preform/ semi-solid alloy interface. This causes a gradational distribution of the primary crystals in part of the obtained material.