Effects of heat-treatment on the interfacial reaction and tensile properties of Al₂O₃ coated-Al₁₈B₄O₃₃w/Al–Mg matrix composites

Highlights: • Heat-treatment has no effect on interphase of composite without whisker coating. • MgAl₂O₄ forms in composite contained coated whisker after heat-treatment. • Heat-treatment affects microstructure and tensile properties of composites greatly. • Highest tensile properties present in composite with coated whisker after treated 12 h. Al–Mg matrix composites reinforced by Al₁₈B₄O₃₃ whiskers with and without Al₂O₃ coating were fabricated by squeeze casting. The effects of heat treatment on the microstructures and tensile properties of the composites were investigated. The results indicated that the heat treatment strongly affects the interphase, the precipitation phases, and the dislocation states in the matrices of the composites. This leads to great changes in the tensile properties of the composites during the heat-treatment process. The heat treatment does not affect the interface reaction of the composite with raw whiskers, but affects that of the composite-contained coated whiskers. After heat treatment for 20 h, a new interface phase of MgAl₂O₄ forms in the composite-contained coated whiskers, which is responsible for the low tensile properties. In addition, the dislocation states and the precipitation phases affect the tensile properties of the composites distinctly. A suitable heat-treatment process can be found for the ultimate tensile strength and elongation to fracture.