The Fretting Fatigue of Commercial Hard Anodized Aluminum Alloy

An investigation has been carried out in order to study the fretting fatigue behavior of a 2014-T6 aluminum alloy, which has been coated with a commercial hard anodizing of approximately 20-25 μm in thickness. The hardness (HV) was significantly improved up to about 380 after hard anodizing coating while the hardness value of original 2014-T6 was 175. Fretting reduced drastically the fatigue life of samples in both conditions, substrate and coated conditions. The application of such a coating to the substrate may increase the fretting fatigue life in comparison with the uncoated samples in low-stress region for rotating bending fatigue loading while at higher stresses the effect of anodizing is reversed. This may be result from early initiation of cracking of hard anodizing film due to high-stress concentration resulting from bulk stresses. On the other hand, the increase in fretting fatigue life in low-stress region may be probably attributed to low coefficient of friction that prevents metal-to-metal contact, which may result in higher fretting fatigue life because of retardation of crack initiation resulting from lower stress concentration compared to the substrate.