Failure analysis of thin cast A357-T6 centre shell induced by casting defect

Abstract

Thin-walled Al-Si alloy precision casting components are used for various applications due to their excellent castability, corrosion resistance as well as high strength to weight ratio. It is very difficult to achieve all the set requirements due to complexity of thin-walled components through casting processes usually used in producing the aluminium alloy castings. A thin-walled shell, used as a housing unit for a component manufactured from A357-T6 alloy, failed prematurely during a torqueing process. The failed component was subjected to chemical analysis, microstructural analysis, visual examination and mechanical testing to identify the nature of the fracture and establish the primary cause of the failure. In the investigation, optical and electron microscopy, hardness and tensile tests were used to study the fracture. The examined fractured surface of the component revealed that, the fracture occurred in a brittle manner. The dominant and leading casting defect identified in the failed shell is porosity. The analysis of the results indicates that coarser grains and porosity defects led to decrease in ductility and thereby causing the shell to fail in a brittle manner.