镁合金AZ31表面无铬磷酸盐转化膜的制备、结构及性能

用化学沉积的方法在镁合金AZ31表面获得了无铬、无氟和无亚硝酸盐的环保型化学转化膜。 SEM，linebreak EDS及XRD分析表明，以磷酸盐和无氟添加剂为主要成分，在镁合金AZ31表面获得了致密、均匀和无网状裂纹的磷化膜。磷化膜厚度为12μm~15 μm，主要物相为MnHPO₄•2.25H₂O， 主要元素成分为O，Mg，P，Mn和Al。磷化后的镁合金AZ31通过中性盐雾测试(NSS)，72 h后未见腐蚀现象，浸涂氨基烘漆后的NSS测试达到204 h未见明显腐蚀，结果表明磷化膜具有良好的耐蚀性能。电化学极化曲线测试结果显示， 磷化后镁合金AZ31的E_corr比未处理的正移111 mV，I_corr至少降低了三个数量级，磷化膜通过抑制阳极溶解和阴极析氢过程，有效地提高了镁合金AZ31的耐蚀性能。

PREPARATION,STRUCTURE AND CORROSION RESISTANCE OF CHROME-FREE PHOSPHATE FILM FOR MAGNESIUM ALLOY AZ31

An environment-friendly phosphate film was obtained on the AZ31 magnesium alloy surface via chemical deposition methods.The morphology,compositions and phase compositions of the film were examined using scanning electron microscopy（SEM）,energy dispersive spectrometer（EDS） and X-ray diffractometer （XRD）.The results show that a dense,uniform and crack-free phosphate film can be prepared using the solution with free of chromate,fluorides and nitrite.The phosphate films are mainly composed of MnHPO₄·2.25H₂O, The film thickness is between 12μm and 15μm and the compositions consist of O,Mg,P,Mn and Al.the film hardly appears corrosion phenomenon for 72 h in the neutral salt spray test（NSS）,and the time could arrive 204 h after the plus paint.The test results indicate that the phosphate film is of good corrosion resistance. Potentiodynamic polarization curves prove that the E_corr with the film is shifted positively 111 mV（vs.SCE）; the I_corr is decreased at least by three orders compared with that of the bare substrate AZ31 respectively.The results show also that the existence of the film has a great inhibitive action on anodic dissolution and restraint action on the cathodic hydrogen evolution,which will effectively improve the corrosion resistance for magnesium alloy AZ31.