Fabrication of aluminum borate whisker reinforced AZ91D magnesium alloy composites by semi-solid process and their mechanical properties

In order to develop a light weight piston for an automobile engine, aluminum borate whisker reinforced AZ91D magnesium alloy composites were fabricated by a semi-solid material process using squeeze casting. By controlling the solid fraction, f_s, and the rate of the infiltration into the preform, we succeeded in reinforcing a part of the cast alloy without deformation of the preform. The tensile strength of the alloy/composites interface fabricated by semi-solid (50% f_s, solid fraction in the semi-solid slurry) process was 120 MPa, and it was equal to the strength by conventional 0% f_s process. However, the flexural strength of the composite by the 50% f_s process was about 10% lower than the strength of that from the 0% f_s process, 498 MPa. After solid solution and aging treatment, the bending strength of the composites in both 0% and 50% f_s process was decreased. This might be caused by the notch effect of Mg₂Si compound produced between SiO₂ binder of the preform and magnesium during heat treatment.