Abstract
Aluminum borate (Al_<18>B_4O_<33>) whisker reinforced ZK60 (Mg-Zn-Zr) and AZ91D (Mg-Al-Zn) magnesium alloy composites were fabricated by squeeze and compo castings. Then influences of precipitate phase on hardness and interfacial reactions were investigated. All composites had good aging ability, but compo casting ZK60 matrix composites has low ability because of interfacial reaction at interface. As aging progressed isothermally, hardness of ZK60 composites decreased after peak aging. Nevertheless, when the hardness of AZ91D composite reached the peak, it would scarcely decrease. The time required to reach peak hardness of composites was shorter than that of monolithic alloy. The increment of hardness by aging treatment was approximately duplicate both monolithic alloy and composite fabricated by squeeze casting. As the ageing progressed distinct precipitates became apparent, sequence of precipitates in ZK60 composite was β_1 (MgZn_2) ⟶β_2 (MgZn_2) ⟶β (Mg_2Zn_3). In AZ91D composite, only continuous equilibrium β (Mg_<17>Al_<12>) phase was observed. After solution heat treatment, the effects of interfacial reactions on aging precipitates were negligible in ZK60 and AZ91D composites.
