六偏磷酸钠对LD7铝合金微弧氧化陶瓷膜结构及耐腐蚀性能的改善作用

Improvement Effect of Sodium Hexametaphosphate on Microstructure and Corrosion Resistance of Micro-Arc Oxidation Coating of LD7 Aluminum Alloy

目前未见采用微弧氧化技术提高LD7铝合金耐腐蚀性能的有关报道。在磷酸盐体系电解液中添加一定量的(NaPO3)6,采用微弧氧化(MAO)技术在其表面原位生成陶瓷层。通过扫描电镜、X射线衍射和电化学极化曲线等方法研究了添加(NaPO3)6对微弧氧化陶瓷层组成、结构及耐腐蚀性能的影响。结果表明:添加(NaPO3)6后膜层厚度增加,表面粗糙度降低,膜层更加平滑致密,微孔数量明显减少;膜层主要由α-Al2O3,γ-Al2O3和少量的AlPO4相组成,以α-Al2O3为主;在3.5%NaCl溶液室温电化学行为中,微弧氧化后其自腐蚀电流密度比基体降低了2个数量级,添加(NaPO3)6后引起了阳极过程阻滞并减少Cl-富集,从而抑制了点蚀,使自钝化趋势得到提高,耐腐蚀性能明显增强。

Ceramic coating was prepared on the surface of LD7 aluminum alloy via micro-arc oxidation in a phosphatic electrolyte system containing sodium hexametaphosphate [(NaPO3)6] additive.The effect of the additive on the composition,microstructure and corrosion resistance of the micro-arc oxidation coating was investigated using a scanning electron microscope,an X-ray diffractometer and an electrochemical test rig.It was found that after adding(NaPO3)6,the thickness,smoothness and compactness of the micro-arc oxidation coating were increased,and its surface roughness and amount of micro-pores were decreased.As-prepared micro-arc oxidation coating consisted of α-Al2O3 and γ-Al2O3 as well as a mall amount of AlPO4.As compared to the corrosion current density of Al alloy substrate,that of the micro-arc oxidation coating in 3.5% NaCl solution was reduced by 2 orders of magnitude.(NaPO3)6 could retard the anodic process and enrichment of Cl-,thereby inhibiting pitting corrosion,enhancing self-passivation and significantly increasing corrosion resistance.