Superplastic Formability and Cavitation Analysis of AA7075 Matrix Composite Reinforced with B4C Particles Produced by Stir Casting

摘要

In this present work, the AA7075 was selected as matrix material and boron carbide (B4C) particles as reinforced material with several weight percentage of B4C particles (2, 4 and 6) and were prepared by two step stir casting technique to distribute the reinforced particles uniformly in the composite. It is one of the method to increase ductility of the composite is superplastic deformation, to exhibit very large elongation without failure. The basic requirement of fine structure superplasticity is the average grain size of the specimen is less than 10 µm; to achieve this fine grain size through the thermomechanical treatment process includes furnace cooling from the solution treatment to the overaging, warm rolling, recrystallization and aging treatment. The superplastic forming and cavitation behavior of the prepared composite under biaxial stress were investigated under constant forming pressure and temperature of 0.2 MPa and 550 °C, respectively. The formability and cavitation effect of composites were entirely different from the normal superplastic alloys. The yield strength and ultimate tensile strength have reduced drastically after addition of 4 B4C particles the main reason was agglomeration of the ceramic particles. In the superplastic forming process the sample B exhibits very high formability of dome height at 16.5 mm compared to the samples A and C. It is due to the uniform distribution of the particles without agglomeration on the grains as well as along the grain boundaries.