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

Abstract

Abstract 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°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 × 10−3 to 5 × 10−1 s−1) compression tests using a thermomechanical simulator at temperatures of 470°C and 500°C. Strain rate jump tests revealed superplastic region with strain rate sensitivity index m = 0.4 in the lower strain rate regime of 1 × 10−3 to 5 × 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.