435 Fatigue behavior of die-cast AM60 alloy under different environmental conditions

Abstract

Four-point bend (Inner span: 10mm, Outer span: 30mm) fatigue tests were carried out with two-groups of AM60 alloy; one group was as-cast and another group was shot-blasted. The as-cast specimens were tested in three different environmental conditions; low humidity (20℃, 55%RH), high humidity (50℃, 80%RH) and 5wt% NaCl corrosive environment while shot blasted specimens were tested in high humidity and 5wt% NaCl environment. In each case, frequency was kept at 20Hz, load ratio at 0.1 together with sinusoidal waveform. S-N curves show that shot blasted specimens present better fatigue life and fatigue strength as compared to those of as-cast specimens under any environmental condition. The lowest fatigue strength was shown by as-cast specimens under NaCl environment. However, fractographic observations did not reveal presence of any corrosion pit which is generally found by other researchers. On the contrary, corrosion induced crack nucleating sites were observed for both groups of alloys and assumed to be the main cause of degrading fatigue strength under aggressive environment. As for shot-blasted specimens compressive residual stress might have been induced during shot blasting which could have delayed initiation of fatigue cracks. Hence they showed better fatigue performance as compared to those of as-cast specimens under different environments.