Effects of T6 treatment on the plasma electrolytic oxidation of Al-Cu alloy fabricated via wire arc additive manufacturing technology

The as-deposit (AD) and heat-treated (HT) Al-Cu alloy obtained via wire arc additive manufacturing (WAAM) technology was coated by plasma electrolytic oxidation (PEO), respectively. The reticular big Al2Cu grains in the AD Al alloy substrate evolved into numerous small particles and nano precipitates after the heat treatment. The thickness and surface roughness of the PEO coatings on both substrates were increased gradually with the increase of oxidation time. The coating on the HT Al alloy was deposited faster with a rougher surface structure. Although most Al2Cu grains were dissolved in the electrolyte at the earlier oxidation stage, some Cu-containing compounds and metallic Cu were gradually deposited in the coatings at the discharge spark oxidation period. The coatings were mainly composed of gamma-Al2O3 and alpha-Al2O3, and the ratio of alpha-Al2O3 was increased obviously with the oxidation time. Besides, the coating on the HT sample consisted of a higher ratio of alpha-Al2O3 than that on the AD alloy, especially at the end of PEO processing. The PEO coatings were made up of two sub-layers, a thin compact inner layer and a porous outer layer. In comparison, the coating on the HT alloy was a bit denser and more uniform. The substrates displayed a adhesion wear trait while the coated samples shew a slight abrasive wear manner over the abrasion test, with a still ball as the friction pair. and the coated HT alloy had a better wear resistance than the coated AD alloy did.