Microstructure Characteristic of Adiabatic Shear Bands for Aluminum Matrix Composites Compressed With High Strain Rates

In this paper, the novel transformed bands in adiabatic shear bands (ASBs) were researched which was characterized as melting or solid to liquid phase transformation. By split Hopkinson pressure bar (SHPB), optical microscope (OM) and scanning electron microscope (SEM), microstructure characteristic in the transformed bands at varied strain rates were observed. From the experimental results, it was found that molten aluminum bands and aluminum balls agglomeration, which called transformed bands, were found on the shearing surface for 55% TiB2/Al composites compressed at strain rates of 1 similar to 2x10(3)s(-1). It was concluded that there were the molten aluminium alloy and the molten aluminium particles on the shear flat surface oriented at an angle approximately 45 degrees to the compression axis, which was transformed band. It was formed due to aluminium alloy melt at high temperature and solidified sharply by analysis. The formation of transformed bands was ascribed to adiabatic temperature rise, which caused aluminum alloy matrix softened and molten. The adiabatic temperature rise was 800-900K by caculation. The local high temperature led to the formation of the molten aluminium particles whose diameter was 1-3 mu m on the adiabatic shear flat surface. With the rapid convergence of molten aluminium particles and growing up, the adiabatic shear band was finally formed.