The Changes of Fatigue Properties in Aluminium Cast Alloy during Solution Treatment

Abstract

This paper describes the effect of solution treatment on the fatigue properties of AlSi9Cu3 cast alloy. The heat treatment consisted of a solution treatment at two different temperatures 515°C and 525°C, a holding time of 4 hours; water quenching at 40°C and natural aging at room temperature for 24 hours. Thus prepared samples were subjected to fatigue test with a rotating bending loading (testing machine ROTOFLEX operating at 30 Hz, load ratio R = -1). The fatigue fracture surfaces were observed using a scanning electron microscope (SEM) after the fatigue test. The results showed that the existence of casting defects (8.4 % of micro-shrinkage) has considerable influence on fatigue properties and can be considered as fatigue crack initiators in what leads to final fatigue damage. Apart from cast defects, the morphology of eutectic silicon and intermetallic phases (Fe- and Cu-rich phases) are also important factors which have an influence on the fatigue properties of Al-Si cast components. The solution treatment used (at 525°C/4hours) has increased fatigue properties (the fatigue lifetime increased from 49 to 76 MPa), thanks to Si particles, morphology changes, and cast defects area reduction as well as reduction Fe-rich phases.