镁合金AZ31锰系磷化膜的生长过程及形成机理

Growing process and formation mechanism of manganese phosphate conversion film of magnesium alloy AZ31

以磷酸二氢锰的盐溶液为研究体系,采用SEM和EDS和电化学分析手段,研究镁合金AZ31锰系磷化膜的生长过程和形成机理。结果表明:磷化膜的生长过程分为5个阶段:基体溶解-成核阶段(0～130 s)、基体和磷化膜溶解阶段(130～630 s)、磷化膜快速生长阶段(630～1 300 s)、磷化膜稳态生长阶段(1 300～2 000 s)和磷化终止阶段(2 000 s以后)。磷酸盐晶核在镁合金AZ31浸入溶液的初始阶段一次形成,并优先在β相表面经过成核—长大—分裂—细化—增厚5个过程,沿表面方向生长和外延,最终形成致密的磷化膜。并且,磷化膜有两层,第一层是以Mg3(PO4)2和AlPO4以及MnHPO4为主的沉积薄膜;第二层则是在β相表面成核—长大的MnHPO4磷化膜。

The growing process and formation mechanism of phosphate film of magnesium alloy AZ31 in the manganese dihydrogen phosphate solution were studied by scanning electron microscopy（SEM）,energy dispersive X-ray spectrometer（EDS） and electrochemical method.The results show that the growing process of phosphate film is divided into five stages： substrate dissolving-nucleation（0-130 s）,substrate and film dissolving（130-630 s）,file rapid growth（630-1 300 s）,film steady growth（1 300-2 000 s） and phosphating finishing（after 2 000 s）.The phosphate crystal nucleuses are firstly formed on the surface of β phase for one time with the magnesium alloy AZ31 immersing.With the growth of the nucleus on the alloy surface,the coverage of the phosphate grains increases gradually and the dense films are obtained.The films are made up two layers： the bottom is a deposition film with compositions of Mg3（PO4）2,AlPO4 and MnHPO4.The second layer consists of MnHPO4 which is formed on the surface of β phase.