Cyclic Deformation and Low Cycle Fatigue Behavior in a 6061Al/22vol% SiC Whisker Composite

Abstract

A 6061Al matrix composite reinforced with 22vol% SiC whiskers and the unreinforced matrix alloy in different aged conditions were examined at the ambient temperature. Total strain controlled cyclic deformation under fully-reversed loading and low cycle fatigue properties were measured. The mechanical test results demonstrated that the composite materials in different aged conditions cyclically hardened at the applied strain amplitudes, typically at 0.4 %, 0.6 % and 0.8 %. The underaged composite specimens showed the most pronounced cyclic hardening, while the overaged composite only hardened to a limited amount at the first a few cycles. It has been found that the addition of SiC whiskers into the 6061Al increased the cyclic stress to the largest extent in the underaged condition while to the smallest in the overaged. The low cycle fatigue resistance of the composite to cyclic straining was found to be inferior to that of the unreinforced matrix alloy. When the saturation cyclic stress amplitude is considered, however, the composite material showed superior fatigue strength to the matrix alloy in this low cycle fatigue region. The experimental phenomena are interpreted in terms of the result of the electron microscopy and the fractography of the fatigue failed samples.