Influence of Microstructure on Cyclic Stress Response and Cyclic Fracture Behavior of Aluminium Alloy Metal-Matrix Composite

Abstract

In this paper the cyclic stress response and fatigue fracture characteristics of an aluminum cast alloy A356 discontinuously reinforced with silicon carbide particulates and strained to failure over a range of strain amplitudes giving lives of less than 104 cycles to failure is presented. The aluminum alloy-ceramic particle composite, in the as-cast condition, displayed combinations of cyclic hardening and softening to failure at higher cyclic strain amplitudes, and progressive softening to failure at low cyclic strain amplitudes. The spray atomized and deposited material showed softening at higher strain amplitudes and hardening to failure at lower cyclic strain amplitudes. The observed hardening and softening behavior are a mechanical effect and attributed to concurrent and competing influences of an increase in dislocation-dislocation interaction, dislocation multiplication and dislocation — ceramic particle interactions leading to microcrack initiation. The fracture behavior of the alloy is interpreted in light of composite microstructural effects, plastic strain amplitude and concomitant response stress.