Investigation On Corrosion Resistance Of Micro-Arc Oxidation Coating On Al₁₈B₄O_33w/6061 Composite

In order to increase the corrosion resistance of Al₁₈B₄O₃₃w/6061 composite, protective coatings were fabricated in silicate and metaphophate electrolyte system by micro-arc oxidation(MAO) surface treatment technique. Microstructure of MAO coatings was observed and analyzed using SEM, TEM, XRD, XPS, EDS, etc. The corrosion resistance and corrosion behaviors of coatings were evaluated by dynamic potential polarizing test and salt immersion test. Growth processes of MAO coatings on 6061 alloy and ABO_w/6061 composite were observed and effects of ABOw whisker on micro-arc oxidation behaviors of ABOw/6061 composite were investigated. Sol-gel sealing process was used to enhance the corrosion resistance of the MAO coatings further.Experiment results show that electrical parameters influence microstructure and growth rate of MAO coatings. The more energy density acts on the MAO coatings, fiercer the disruptive discharge is, more chaotic the microstructure and thicker the coatings are.The coating is mainly composed ofγ-Al2O3 and a small amount of other components through the electrolyte introduction, changing electrical parameters can not obtain other phases.The existence of ABOw whisker modifies the position of the disruptive discharge during the primary stage of MAO. The disruptive discharge first occurs in crystal boundary in 6061 alloy but the interface between ABOw whisker and Al in ABOw/6061 composite respectively.With energy density of MAO increased, the corrosion resistance of MAO coatings of 6061 alloy was improved to some extent, but because of the introduction of ABOw whisker, the microstructure of MAO coatings was modified and then the corrosion resistance of MAO coatings of ABOw/6061 composite exhibits the tendency opposites 6061 alloy. Under immersion corrosion condition, the MAO coating obtained on 6061 alloy and ABOw/6061 composite show different corrosion behaviors.The corrosion resistance of the MAO coatings of ABOw/6061 composite will be improved further more after the sealing process uses the TiO₂ thin film sealing the MAO coatings surface, and the corrosion resistance is better when the diping times are 1². After annealing treatment, the TiO₂ thin film is mainly composed of the small grain size's anatase. With the inrease of annealing treatment time, the degree of crystallization of the TiO₂ thin film is more complete and then causes the better corrosion resistance.