Abstract:
Plasma electrolytic oxidation (PEO) of 5005 aluminum alloy was carried out in KOH-red mud electrolytes. Effects of KOH mass concentration (
CKOH=1.0, 2.0, 3.0, 4.0, 5.0 g·L
-1) on the critical arcing voltage of PEO and the thickness, phase composition, morphology and bonding strength of the ceramic coating were analyzed. The results show that the ceramic coatings prepared in electrolytes with different KOH content were mainly composed of γ-Al
2O
3 and α-Al
2O
3, but a small amout of CaCO
3, SiO
2 and Fe
2O
3 phases also appeared. When KOH content increased, the positive and negative critical arcing voltages of PEO decreased rapidly; the coating thickness showed a growth trend of "semi-parabolic" shape; the γ-Al
2O
3 content in the ceramic coating increased first, then decreased and then increased, the change trend of α-Al
2O
3 content was just the opposite, and the CaCO
3, SiO
2, Fe
2O
3 content increased first and then decreased; the surface porosity of the ceramic coating decreased first and then increased, the surface roughness kept increasing and the hardness and bonding strength increased first and then decreased.