Effect of alumite surface treatments on long-life fatigue behavior of a cast aluminum in rotating bending

Alumite treatment is one of surface treatments for aluminum alloy and it provides an oxide layer (Al2O3) on the surface by anodizing. The oxide layer is called “alumite” in Japanese industry. This method has been widely used for aluminum alloy because the alumite possesses characteristics such as high hardness, wear resistance, and electrical resistance. In order to examine the effect of alumite layer on the fatigue behavior, fatigue tests were carried out on aluminum alloy specimens with two different alumite treatments by means of a dual-spindle rotating bending fatigue testing machine. Tests were also conducted on untreated specimens for comparison. Fracture surfaces of all the failed specimens were examined in a scanning electronic microscope (SEM). Fatigue fracture mechanisms are discussed in the light of fractography and fracture mechanics. As results of fatigue tests, significant deteriorations of the fatigue strength for alumite-treated specimens having each thickness of the alumite layer were observed in comparison with the results for untreated specimen in the short life regime. However, in long-life regime of >107, the fatigue strength of alumite-treated specimen having 3 μm alumite layer becomes a little higher than the results for untreated specimen.