THE INFLUENCE OF OXIDE INCLUSIONS ON THE POST-HIP FATIGUE LIFE OF TWO AL-SI-MG CASTINGS

摘要

Hot isostatic pressing (HIP) has a long been used in aerospace applications where, through the elimination of microporosity, the fatigue life of a casting is improved. In recent years, process and equipment improvements have resulted in reduced processing costs, especially as applied to aluminum castings, thus making HIP a viable option in price critical, non-traditional markets. Past trials that evaluated the effect of HIP on aluminum castings have produced mixed results. Post-HIP improvement in fatigue resistance could be large, small or non-existent. Investigation revealed that oxides can have a strong, negative, effect on post-HIP fatigue properties. This study reviews existing theory on the influence of porosity and inclusions on fatigue life and, using experimental data from a program aimed at integrating HIP and heat treat into a single process, shows how variations in oxide concentration can decrease or eliminate the improvement in fatigue life normally associated with hot isostatic pressing.