Abstract
Magnesium matrix alloy composites was fabricated employing Mg–4 mass%Zn–0.2 mass%Ca alloys as a matrix alloy and aluminum borate whisker as a reinforcement fiber by squeeze casting. Relationships between the fabrication conditions and the soundness of composites, and the aging characteristics and high temperature tensile properties of the obtained sound composites were investigated. As the preform sintering temperature raises, the preform compressive strength increases without the crystal structural changes up to 1400°C. As the preform sintering and pouring temperatures increase, the area of the preform cracking and non-infiltrating region decrease, resulting in the reduction of tensile strength scatter at room temperature. MgO polycrystalline layer with a thickness of the order of 0.1 μm is created at whisker-matrix interface and enhances the bonding strength at the interface. Precipitates finely distribute and amount of age hardening slightly increases by pre-aging at 50~70°C for 24 h before aging at 180°C for 1 h, but the strength of the composites is unchanged. As-cast and T7-treated composites reinforced with 26 vol% aluminum borate whisker has the tensile strength of 350∼360 MPa at room temperature, whereas exhibits that of 130~140 MPa at 250°C. SEM fractographs suggest that the considerable softening of matrix alloy at 250°C makes easy to debond at the edge of whisker at 250°C and that crack propagation in the matrix is easy due to the fine distribution of the whisker.
