Growth process and wear resistance for ceramic coatings formed on Al–Cu–Mg alloy by micro-arc oxidation

The growth process, distribution of chemical elements, phase constitutions and relative wear resistance of the ceramic coatings formed on Al– Cu–Mg alloy by ac micro-arc oxidation are investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscope (EDX), Xray diffraction (XRD) and reciprocating friction and wear tests. The results indicate that there are three stages with the formation of the ceramic coatings: (1) the formation of ceramic particles, (2) sintering growth in sawtooth structure, (3) the increase of thickness by remolting and sintering. The ceramic coatings are made up of a mixture of a-alumina, g-alumina and amorphous alumina, whose relative contents varied with the position in the ceramic coatings, respectively. The chemical elements altered in ceramic coatings produced in different electrolytes and varied along the depth in ceramic coatings obtained in phosphate electrolyte. Meanwhile, the results of friction and wear tests against Gr15 after 16 h indicate that the weight loss of ceramic coatings became almost unchanged