Corrosion wear behaviors of micro-arc oxidation coating of Al2O3 on 2024Al in different aqueous environments at fretting contact

The fretting wear behavior of micro-arc oxidation (MAO) coating of Al2O3 on an aluminum alloy 2024Al flat against a 440C stainless steel ball was investigated in artificial rainwater, artificial seawater and distilled water by using a ball-on-flat configuration with 300 mu m amplitude at room temperature for 1 h. The morphology of the wear scars were observed and analyzed using scanning electron microscopy; the 3D-morphology and wear volume-loss were determined using a non-contact optical profilometer. Potentiodynamic anodic polarization was used to measure the corrosion behavior of the MAO coating before and after the corrosion wear test. The influences of the load, frequency and aqueous medium on the friction coefficient and wear volume-loss of the coatings were also analyzed. Results show that the friction coefficient decreases generally with an increase of the frequency in the three aqueous solutions; whereas it presents different variation trends as the load increased. In addition, aqueous environment does significantly influence the friction coefficient, the friction coefficient was the largest when fretting occurred in distilled water, smaller when fretting occurred in rainwater, and the smallest when fretting occurred in seawater. Particularly the remarkable antifriction effect of the seawater is of note. The wear-loss of the MAO coating in the distilled water is the largest at low frequency; however, it increases rapidly in rainwater and seawater at high frequency due to the corrosion effect of Cl- ion as well as its accelerating effect to the wear process, and results in larger wear-loss than that in distilled water, which implies a positive synergism between corrosion and wear. (C) 2009 Elsevier Ltd. All rights reserved.