摘要
提出了一种压铸镁合金AZ91D表面磷酸盐化学转化工艺,其配方及操作条件为:磷酸8mL/L,氧化锌3g/L,酒石酸3g/L,氨水4g/L,硝酸钠3g/L,氟化钠1g/L,温度25～30°C,时间5min。研究了该无铬转化膜的表面和截面形貌,化学成分,物相组成,结合力,孔隙率和耐蚀性。结果表明:磷酸盐转化膜主要由Mg、Zn、Al12Mg17和Zn3(PO4)2·4H2O组成,结合力均≥8分,孔隙率由封孔前的27.91%降为封孔后的6.98%,耐中性盐雾时间均可达到24h。电化学实验结果显示,转化膜的腐蚀电位比基体提高了64mV,封孔处理后腐蚀电位提高了122mV,腐蚀电流密度均降低了两个数量级。
A phosphate chemical conversion process on the surface of die-cast magnesium alloy AZ91D was developed.The bath composition and operation conditions are as follows：H3PO4 8 mL/L,ZnO 3 g/L,tartaric acid 3 g/L,NH3·H2O 4 g/L,NaNO3 3 g/L,NaF 1 g/L,temperature 25-30 °C,and time 5 min.The surface and cross sectional morphologies,chemical and phase compositions,adhesion strength,porosity and corrosion resistance of the chromium-free conversion coating were studied.The results showed that the phosphate conversion coating are mainly composed of Mg,Zn,Al12Mg17 and Zn3（PO4）2·4H2O and has an adhesion not less than score 8.The porosity of the conversion coating was decreased from 27.91% to 6.98% after sealing treatment.The time of neutral salt spray test of the conversion coating reached 24 h.The results of electrochemical experiments indicated that the corrosion potential of the conversion coating is positively shifted by64 mV before sealing and by 122 mV after sealing,as compared with the AZ91D Mg alloy substrate.The corrosion current density of AZ91D Mg alloy substrate is decreased by two orders of magnitude after the conversion treatment and further sealing.
出处
《电镀与涂饰》
CAS
CSCD
北大核心
2010年第10期32-36,共5页
Electroplating & Finishing
基金
广东省自然科学基金(9151065101000002)
关键词
镁合金
磷酸盐转化膜
封孔处理
耐蚀性
电化学
magnesium alloy
phosphate conversion coating
sealing treatment
corrosion resistance
electrochemistry
作者简介
高阳（1985-），男，湖北鄂州人，硕士研究生，主要研究方向为金属表面处理（包括化学转化、物理气相沉积等）。
通讯作者：代明江，教授级高工，（E-mail）daimingjiang@tsinghua．org．cn。
