Compressive Flow Behavior and Microstructural Evolution of Friction Stir Processed A356-5% B4C Composite

An Al-7Si-0.3Mg (A356) alloy reinforced with 5 % boron carbide (B4C) particulates was produced through squeeze casting technique at a temperature of 710 degrees C. Friction stir processing (FSP) was employed on an A356-5% B4C composite with optimized parameters, viz., tool advancing speed of 15 mm/min and tool rotation speed of 250 r/min for one pass and two passes. High-temperature flow behavior of the FSPed A356-5% B4C composite was investigated by strain rate jump (1 x 10-3 to 5 x 10-1 s-1) compression tests using a thermomechanical simulator at temperatures of 470 degrees C and 500 degrees C. Strain rate jump tests revealed superplastic region with strain rate sensitivity index m = 0.4 in the lower strain rate regime of 1 x 10-3 to 5 x 10-2 s-1. However, the value of m reduced to 0.3 upon two-pass FSP. The reduction in m is attributed to the more uniform redistribution of hard Si particles throughout the composite, as examined by microstructure evolution in scanning electron microscopy, linked with energy dispersive spectroscopy and electron-backscattered diffraction facility.