EFFECT OF GRAPHITE ADDITIVES IN ELECTROLYTES ON CHARACTERISTICS OF MICRO-ARC OXIDATION COATINGS ON 7E04 ALUMINUM ALLOY

Abstract

Micro-arc oxidation coatings were fabricated on 7E04 aluminum alloy substrates by micro-arc oxidation (MAO) in the electrolytes with the graphite addition varying from 0 to 8[Formula: see text]g/L (0, 2, 4, 6, 8[Formula: see text]g/L). The effect of graphite concentration on the surface morphologies, micro-hardness, thickness, phase composition and corrosion resistance of coatings was investigated. With the graphite powder concentration increasing, the oxidation voltage decreased gradually and the thickness of coatings firstly dropped down and then went up. It is found that the size of micro-pores and sintered discs declined with increase of graphite concentration. The XRD results indicated that MAO coatings mainly consisted of [Formula: see text]-Al2O3, [Formula: see text]-Al2O3, SiO2 and a little [Formula: see text]-Al2O3. The corrosion resistance of coatings was improved with the addition of graphite powder. The study reveals that the appropriate graphite powder in the electrolytes is essential to promote the performance of the coatings.