Improvement of High Cycle Fatigue Properties by HIP Treatment for Cast Alminum Alloys.

Abstract

Rotating bending fatigue tests were carried out on three kinds of cast aluminum alloys after hot isostatic pressing (HIP) treatment. The HIP treatment was carried out to reduce cast defects and porosity of cast aluminum alloys. Efficacy of HIP treatment varied from material to material, but in the material which treatment was most effective, namely AC4CH, the fatigue strength was markedly improved. In the HIP-treated AC4CH, the fatigue crack initiation site was not a cast defect but a part of the specimen surface with a high density of eutectic silicon particles. Comparing the HIP-treated AC4CH with conventional AC4CH, crack propagation behavior was the same for both, but crack initiation life was longer for the former than the latter. Fatigue life was successfully evaluated considering lives of both crack initiation and crack propagation. Here, the crack initiation life was defined as involving scatter immediately after crack initiation, and the crack propagation life was expressed in one relation for the HIP-treated materials and the conventional material.