MULTISTAGE FATIGUE MODELING OF CAST A356-T6 AND A380-F ALUMINUM ALLOYS

摘要

This paper presents a multistage fatigue model with microstructure-property relations of descending order capturing deleterious effects of inclusions: (1) pores or oxides greater than 200 microns, (2) pores or oxides greater than 100 microns near the free surface, (3) 60-90 microns pores or oxides with large volume fractions, (4) pores or oxides less than 60 microns with large volume fractions, and (5) pores or oxides with low volume porosity fractions. This signifies different casting features dominating fatigue life. Capturing the initial cyclic response, the incubation stage is modeled. Assuming a near-micron initial crack size, microstructurally small cracks (MSC) initiate and grow to several dendrite cell sizes until long crack behavior takes over. Usually, 60-80% of the fatigue life is spent in the incubation and MSC stages. Using the multistage fatigue model, two different cast aluminum alloys (A356-T6 and A380-F) were studied in context of actual cast shapes.