Wear performance of composite dual-layer coated Al-12Si alloy: Effect of Al₂Ce reinforcement and micro-arc oxidation

An attempt has been made to enhance the wear resistance of Al-12Si alloy by forming a dual-layer coating consisting of an Al-12Si matrix composite layer (Al-12Si + ∼40 vol % Al₂Ce) and an external composite oxide layer. While the hardness of monolithic Al-12Si alloy was ∼110 HV, the Al-12Si matrix composite layer has got hardness of ∼140 HV and exhibited ∼6 times higher sliding wear resistance due to the suppression of the plasticity-induced adhesive wear by Al₂Ce particles. Applying micro-arc oxidation (MAO) as a post-treatment favoured an oxide layer (Al₂O₃) on the Al-12Si alloy and a composite oxide layer (CeO₂ + Al₂O₃) on the Al-12Si matrix composite layer. The MAO coatings fabricated on the Al-12Si alloy and Al-12Si matrix composite layer, with hardness of ∼11 GPa and ∼13 GPa, respectively, provided more than two orders of magnitude increase in the wear resistance by shifting the wear mode to elasticity-dominated wear. However, the critical load imposing the complete detachment of the MAO coating by intense cracking and spallation during testing was determined as 3 N for the MAO'ed Al-12Si alloy and 5 N for the MAO'ed Al-12Si matrix composite layer. The wear resistance of the MAO coating of the Al-12Si matrix composite layer was ∼2 times higher than that of the MAO coating of the Al-12Si alloy below the critical test loads, where the coatings remain intact with the substrate.