高稀土镁合金微弧氧化电解液工艺研究

Electrolyte Parameters of Micro-Arc Oxidation for High Rare Earth Magnesium Alloy

通过微弧氧化进行镁合金表面防护处理。经过分析,采用阶梯降压法控制工艺参数,对电解液各个参数进行正交试验,并通过中性盐雾试验得到的腐蚀面积比例和金相观察的膜层厚度作为指标进行极差分析,以得出最优电解液配比,然后通过OM、XRD和扫描电镜膜层厚度、相组成以及表面形貌进行分析。结果发现,当选取电压为550、500、450V(采用阶梯降压法下的电压控制制度),负电压为250V,占空比为20%,氧化时间为50min时,通过极差分析可以得出最优电解液配比:硅酸钠为20g/L,四硼酸钠为40g/L,NaOH为20g/L,络合剂(柠檬酸钠)为15g/L,三乙醇胺为15mL/L,醋酸镍为0.12g/L,其中对成膜影响最大的是硅酸钠。由XRD和EDS分析可知,氧化层主要由尖晶石相六方密堆结构的Mg2SiO4、立方结构的MgO、MgSiO_3、MgCO_3以及Ni_2O_3相等组成,同时含有少量的Na、Gd等元素。

In order to solve the problems of poor corrosion resistance of high rare earth magnesium alloy,the surface treatment of magnesium alloy was performed by micro-arc oxidation to improve its corrosion resistance.For the micro-arc oxidation process adopted,based on analysis,the step-down method was used to control the process parameters,and the orthogonal test of each parameter of the electrolyte was analyzed.The ratio of the corrosion area obtained by the neutral salt sprayed testing and the thickness of the film observed by the metallographic phase were used as indicators to obtain the optimized electrolyte parameters.The thickness,phase composition and surface morphology of each group in the orthogonal experiment were analyzed by OM,XRD and SEM.The results reveal that when the voltages of each stage are 550 V,500 Vand 450 V,respectively(using the voltage control system under the step-down method),with the negative voltage of 250 V,the duty ratio of 20%and the oxidation time of 50 min,the optimized electrolyte parameters can be obtained by range analysis:sodium silicate of 20 g/L,sodium tetraborate of 40 g/L,NaOH of 20 g/L,triethanolamine of 15 ml/L,nickel acetate of 0.12 g/L,a complexing agent(sodium citrate)of 15 g/L,where odium silicate presents the most importance.The film analysis by XRD and ED reveals that the film is mainly composed of the spinel phase Mg2SiO4,cubic structure of MgO,MgSiO3,MgCO3 and Ni2O3 as well as a small amount of Na,Gd and other elements.