Fatigue fractography of particulate-SiC-reinforced Al (A356) cast alloy

Abstract

Fatigue fractography of cast particulate-SiC-reinforced Al(A356) metal matrix composites was carried out. In the low cycle regime, the features on the fracture surfaces, mainly distorted dimples and cracked and also debonded SiC particles, are similar to those found in uniaxial tension. However, in the high cycle regime, extensive slip behavior in the aluminum matrix and relative movement between the two sides of the fracture surface produced some special appearances, namely large flat aluminum matrix areas with characteristic line patterns and step-like fracture surface regions. Mechanisms for the formation of the above phenomena are proposed. In particular, the constraint exerted by reinforcing particles distributed along grain boundaries on the cyclic deformation as well as fatigue crack propagation in the corresponding aluminum grains is discussed. In all samples studied, it is found that fatigue cracks were usually initiated at processing defects, such as casting shrinkage and unwetted SiC particle clusters.