以磷酸盐化学转化膜为研究体系,采用SEM、XRD、OCP等分析方法及检测手段,研究AZ91D镁合金系磷酸盐化学转化膜的成膜机理、膜层结构及生长过程.研究发现AZ91D镁合金在磷化液中成膜过程分5个阶段:初始成核(1～5s)、基体快速溶解(5～60s)、晶体快速生长(1～2min)、膜层稳态生长(2～10min)和膜层沉积溶解平衡阶段(10min以后).AZ91D镁合金表面的磷酸盐晶核的形成并非在金属进入溶液的最初时刻一次形成,是分批形成.最先形成的晶核逐渐长大,新的晶核不断生成,磷酸盐晶粒对其表面的覆盖度逐渐增大,直至各个晶粒逐渐长大相互接界,将其表面完全覆盖,结晶过程结束.晶核的形成未优先发生在基体金属的晶界上,随着晶核的生长和外延而形成磷化膜.
The formation mechanism,coating structure and growing process of zinc phosphate coating on AZ91D magnesium alloy were studied by means of scanning electron microscopy(SEM),X-ray diffraction(XRD),open circuit potential(OCP) .The results show that the growing process of zinc phosphate coating on AZ91D magnesium alloy forming in the phosphating bath process is divided into five stages: the initial nucleation stage(1-5s),the rapid dissolution stage(5-60s),the rapid growth stage(1-2min),steady-state growth stage(2-10min) and the deposition-dissolution equilibrium stage(after 10min).The hopeite phosphate coating on AZ91D magnesium alloy formed in the zinc phosphating bath by batches.The first batch of hopeite nucleus grow into grain gradually,continuous nucleation of new generation occurred simultaneity.The coverage of phosphate grain increased gradually on the alloy surface,the boundary of grain growing closed,and the phosphating process is end until the entire surface is completely covered.With the growth of nucleation and its epitaxial,the phosphate coating formed of on AZ91D magnesium alloy,which is not occured in the metal matrix of the grain boundary with priority.
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