δ‐Ａｌ２Ｏ３短繊維および９Ａｌ２Ｏ３・２Ｂ２Ｏ３ウィスカハイブリッド強化Ｍｇ‐Ｚｎ‐Ｃａ合金複合材料の組織および機械的性質

Abstract

The purpose of this study is to develop hybrid-reinforced Mg–4%Zn–0.2%Ca alloy matrix composites for an application to automobile engine piston. The alloy was squeeze-cast into composites using preforms with a volume fraction of 20% of hybridized aluminum boride whisker and alumina short fiber, and the effect of hybrid ratios, shapes and dimensions of the reinforcement materials on the structure and mechanical properties of the composites were investigated. Prediction of the tensile strength of the hybrid composites was also carried out by adding an increment of the strength due to an increment of dislocation density stemming from difference in the thermal expansion coefficient between the matrix and reinforcement materials to the strength calculated by using the conventional mixture rule. The reduction in tensile strength with temperature, which was serious in the composites reinforced with aluminum boride whisker, was suppressed by mixing alumina short fiber. As the hybrid ratio of aluminum boride whisker increased, tensile strength of the composites at room temperature increased, although the hardness peak in the aging curve became unclear and the age-hardenability decreased. The predicted tensile strength of the hybrid composites at room temperature was in good agreement with the experimental one.