镁合金锡酸盐化学转化膜生长过程研究

Growth Process of Stannate Conversion Coating on Magnesium Alloy

采用环保型锡酸盐化学转化工艺,并利用扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射(XRD)和全浸腐蚀试验等手段,研究了AZ91D镁合金锡酸盐化学转化膜不同生长阶段的形貌特征及其耐蚀性。结果表明,整个过程可分为3个阶段,成膜初期,膜重迅速增加,在α相上生成MgSnO3;约10min后膜的生长速度减小,锡酸盐开始在β相上沉积。此后,膜溶解速度加快,由于α相上的锡酸盐颗粒间隙远大于β相上的颗粒间隙,金属的溶解主要发生在α相上。同时新的膜不断生成,达到动态平衡。此后,随时间延长,膜溶解速度大于成膜速度,膜重减小。经化学处理30min左右,锡酸盐膜层的耐蚀性最好。

The surface morphology and corrosion resistance of the stannate conversion coating on AZ91D magnesium alloy at different grow stages were investigated by SEM(scanning electron microscope),EDS(energy diffraction spectrum) and XRD(X-ray diffraction) as well as salt immersion testing.The results show that in the initial stage of chemical treatment,the MgSnO3 coating is deposited on the α phase very fast,resulting in the rapid increase of coating weight.After 10 min,the stannate conversion coating is deposited on the β phase with the decrease of growth rate.Then,the dissolution of conversion coating is accelerated on the α phase as a result of its loose structure,meanwhile,new coating is continuously deposited on the α phase,resulting in the dynamic balance.With increasing in chemical treatment time,the dissolution rate of coating is higher than deposition rate,which leads to the decrease of coating weight.The stannate conversion coating exhibits desirable corrosion resistance after chemical treatment for about 30 min.