Growth And Property Of AL₂O₃-ZrO₂ Compound Ceramic Layer On AL-Si Alloy By Micro-arc Oxidation

Based on the question of the single Al2O3 micro-arc oxidation coating can not satisfy the use requirement of Al-Si alloy, the Al2O3-ZrO2 compound ceramic layer was produced on Al-Si alloy by micro-arc oxidation. The effect of electrolyte and electrical parameters on coating's thickness and thermal insulation property are studied by single factor experiment. The composition, structure and growth process of the coating are investigated by SEM and XRD. The adhesion, heat resistance, wear resistance and thermal shock resistance were tested by various types of equipments, such as tensile testing machine, insulation testing device, friction and wear testing machine. The results show that:the electrolyte is composed of K2ZrF6 and KOH and the best concentration is K2ZrF6 4g/L, KOH 4g/L, in the reaction, the coating's thickness and thermal temperature increased first and then decreased with the increases of concentration; the best technolgy parameters are current density 10A/dm2, frequency 300Hz, positive pulse number 15, duty cycle 30%, the temperature of electrolyte 70℃, reaction time 30min; the growth of the coating is divided into uniform growth stage and slow growth stage, the growth rate is 2.5μm/min and 1μm/min respectively, the growth direction of the coating is from inside to suface in the initial reaction, and from surface to inside in the fowlling reaction, the rate of growth which from the coating's surface to inside determine the total growth rate; with the increase of oxidation time, the coating's surface micromorphologies are turnly presented as "smoke like", "small bump like", "volcano like", " loose rock like; the crossing micromorphology is divided into transition layer, compact layer and porous layer from inside to surface, the thickness of compact layer accounts for 60%～70% of total thickness, the transition layer is metallurgical bond with substrate; the coating consists ofα-Al2O3,γ-Al2O3,m-ZrO2 and t-ZrO2, t-ZrO2 is the main phase, in which, theα-Al2O3 plays the role of stablizing t-ZrO2; the insulation temperature of the coating can reach 30℃, and the bonding strength is as high as 10.66Mpa, the coating also has good wear resistance and thermal shock resistance.