Relative performance of alumina coatings prepared by micro arc oxidation and detonation gun spray on AA 6063 under plain fatigue and fretting fatigue loading

The present study compares the performance of alumina coatings prepared by two different methods (micro arc oxidation (MAO) and detonation gun (D-gun) spray) on AA 6063 (Al alloy) fatigue test samples under plain fatigue and fretting fatigue loading. While MAO coating had comparable proportions of γ-Al2O3 and α-Al2O3, D-gun sprayed coating contained γ-Al2O3 with minimal quantities of α-Al2O3. MAO coating was relatively harder than D-gun sprayed coating. As both types of coated samples were ground, they exhibited almost the same surface roughness. D-gun sprayed alumina coated samples exhibited slightly higher magnitude of surface residual compressive stress compared with MAO coated specimens. Both types of coated samples experienced almost the same friction force. D-gun spray coated samples exhibited superior plain fatigue and fretting fatigue lives compared with MAO coated specimens. This may be attributed to layered structure of the D-gun sprayed coating.