铝合金微弧氧化过程的特性研究及机理分析

Characteristics and Principle Analysis of Micro-arc Oxidation on Al Alloy Surface

在硅酸钠和氢氧化钾电解液中利用微弧氧化方法,在2024铝合金上制备了陶瓷膜层。测定了膜层的厚度,考察了微弧氧化过程中放电参数及形成陶瓷膜速率的规律,用X射线衍射仪(XRD)观察分析了其成分及组成,对陶瓷膜的摩擦性能进行了研究,推断了在电极上发生的反应,对陶瓷膜的成膜机理进行了分析。结果表明,随着时间的进行,阴阳极电压逐步升高,开始时膜厚增加较快,以后逐渐变慢,膜层厚度随时间变化不是简单的线性关系。陶瓷膜内含有γ-A l2O3和-αA l2O3相,膜层内外两相含量差异较大,主要是由于冷却速率不同的原因。陶瓷层表面经历了一个熔融、凝固和冷却的过程。陶瓷层由内向外可以分为过渡层、致密层和疏松层,陶瓷膜与基体的结合非常牢固,属于冶金结合。溶液内的S i、K元素和基体内的合金元素Cu在陶瓷膜中都有存在,阴极成分Fe也存在于陶瓷膜中,放电通道中在高的能量密度下生成了S i-A l-O三重复杂化合物。

Ceramic coatings prepared on Al alloy surface in sodium silicate （Na2SiO3 ） and potassium hydroxide （KOH） solutions by micro-arc oxidation were studied. The thickness, hardness and adhesion strength of the coatings were all measured. The parameter of discharge and rate of ceramic coating formation were investigated. The elements of the coatings by X-ray diffraction （XRD）were analyzed. The reactions on the electrode surface were deduced and the formation principle of coating was analyzed. The results show that the voltages on anode and cathode increase with time ; cathode voltage is lower than that of anode. The anode peak current increases fast at beginning, and stabilizes for a time, then reduces to a steady value. The same trend applies to the formation rate of oxide film, and the relation between thickness and reaction time is not linear. Moreover, the coating formation rate increases with high current density to a certain extent. The current in MAO process consists of surface discharge current, anodic oxidation current and other current causing secondary electrochemical reaction. The elements of electrolyte （K, Si） and substrate （Cu） appear in the coatings. Moreover, the element of cathode （Fe） appears. The Si-Al-O complex compound is formed in the discharge channels due to high energy density condition.