Effect of Liquid Hot Isostatic Pressing on Structure and Mechanical Properties of Aluminum Gravity Die Castings

Effect of liquid hot isostatic pressing (LHIP) on structure and mechanical properties of an A356.0 alloy was examined. Samples from this alloy were produced by gravity die castings. Part of these samples was subjected to homogenization annealing, and the other part was subjected to LHIP following homogenization annealing. All samples were water quenched from the temperature of prior homogenization annealing or LHIP and finally aged. It was shown that the LHIP processing leads to increase in yield stress, ultimate stress and total elongation. A significant increase in fatigue strength and decreased the scattering of fatigue data takes place too. This is caused by the fact that the fatigue crack initiation mostly occurs on lateral surfaces of the samples subjected to LHIP, whereas shrinkage voids in the non-hipped condition play a major role in crack initiation. In addition, crack propagation under fatigue occurs in samples subjected to LHIP in essentially ductile manner. Thus, LHIP eliminating shrinkage porosity enhances significantly mechanical properties and reliability of aluminum casting.