Effects of strontium modification and hydrogen content on fatigue behavior of A356.2 al alloy

摘要

The effects of strontium modification and hydrogen content on fatigue behavior have been investigated in a casting aluminum alloy (A356.2) under axial loading with strain/stress ratios of 0.1. The alloy was cast in a permanent mold to produce plates with a thickness of approximately 12 mm. After heat treating to the T6 condition, specimens for axial fatigue testing were removed. A356.2 without strontium modification shows better fatigue life as a result of less porosity. A356.2 modified with Sr (0.004-0.006%) and a hydrogen content of 0.19-0.22 cc/100 g shows a higher fatigue life than specimens with hydrogen levels of 0.31 cc/100 g. Pores as small as 75 μm were the predominant crack-initiation sites under high-cycle fatigue; one crack-initiation site was found at the silicon particles within the eutectic constituent in a specimen without strontium modification. In these permanent mold castings, the deleterious effect of pores overshadowed the beneficial effect that Sr modification might have had on improving the fatigue behavior.