3D characterization of fatigue damage mechanisms in a cast aluminum alloy using X-ray tomography

Abstract

Specimens of an Al-Cu-Si alloy were manufactured using die casting without additional machining. These specimens contained various kinds of natural defects were subjected to fatigue loading. The role of these defects was analyzed using fractography, X-ray tomography, and Finite Element simulations. Special emphasis was placed on the interaction between shrinkage pores and gas pores, and on internal flaw extension. It was found that multiple cracks can be initiated from shrinkage pores, and that lifetime is reduced considerably, if gas pores and shrinkage pores interact. Otherwise, the almost defect free casting skin restricted crack extension from shrinkage pores to internal crack advance with corresponding low crack growth rates. The role of the different defect categories in the fatigue damage accumulation process can be explained from a Finite-Element analysis of typical defects which showed that similar values of the stress concentration factor occurred at several locations on a typical shrinkage pore, and at irregular shaped gas pores.