AZ91D镁合金电镀镍及其耐蚀性能研究

发布时间：2018-03-07 02:23

本文选题：AZ91D镁合金　切入点：重复浸锌　出处：《湘潭大学》2017年硕士论文　论文类型：学位论文

【摘要】：镁合金具有低密度、高比强度、高比刚度以及良好的导电性能和电磁屏蔽性能等优点,在航空航天、汽车和电子工业等领域有广阔的应用前景,但镁合金较差的耐蚀性能是限制其实际应用的主要因素之一。电镀方法是提高镁合金耐蚀性能的有效途径之一,然而镁在常规的电镀液中极不稳定。如何对镁合金表面进行预处理并找出合适的镀液和电镀工艺成为当前该领域的研究热点。因此,本论文以AZ91D镁合金为研究对象,开展了镁合金表面预处理及电镀镍工艺研究,同时对电镀后镁合金的耐蚀性能进行了评估。本文的主要研究如下:(1)对AZ91D镁合金电镀表面预处理工艺(酸洗、活化、浸锌等工艺)进行了研究,结果表明,经本工作配制的酸洗液(磷酸242mL/L+浓硝酸12mL/L)酸洗40s后进行活化浸锌(活化4min、浸锌15min)后得良好的浸锌效果,且(酸洗活化后)样品表面残余氧化物的去除以及更少的坑蚀有利于浸锌层的沉积,进一步研究发现重复浸锌后再进行电镀镍制备的电镀镍层成分均一且其结合力优于一次浸锌。(2)对AZ91D镁合金电镀镍工艺进行了研究,对比分析了脉冲电镀镍工艺和直流电镀镍工艺对镀镍层的影响。结果表明,采用直流电镀的电镀效率优于脉冲电镀,而对于脉冲电镀(脉冲频率1000Hz+电流密度为1.25A/dm2),占空比为20%、80%时电镀效率较高,而直流电镀(电流密度为1.25A/dm2)以及脉冲电镀(脉冲频率1000Hz+占空比为60%和80%+电流密度为1.25A/dm2)均可在AZ91D镁合金表面制备出成分均一的电镀镍层,直流电镀镍所得镀镍层耐蚀性能最好,且镍镀层与基体结合力均符合热震测试标准(美国材料协会标准ASTM B571-97)。(3)对AZ91D镁合金电镀铜镍复合镀层的工艺进行了研究,本文找出了一种适用AZ91D镁合金的电镀铜镀液配方,并采用该配方制备出了界面结合紧密、覆盖良好的铜镀层。在此基础上采用脉冲电镀镍(脉冲频率1000Hz+电流密度为2A/dm2+占空比80%)和直流电镀镍(电流密度为2A/dm2)均制备出成分均一的电镀镍层,其中直流电镀制备的复合镀层的耐蚀性能优于脉冲电镀镀层,镍镀层纳米硬度达3.66GPa远高于镁合金基体,铜镍镀层与基体结合力均符合热震测试标准(美国材料协会标准ASTM B571-97)。
[Abstract]:Magnesium alloys have many advantages, such as low density, high specific strength, high specific stiffness, good electrical conductivity and electromagnetic shielding, etc., and have broad application prospects in aerospace, automotive and electronic industries. But the poor corrosion resistance of magnesium alloy is one of the main factors restricting its practical application. Electroplating is one of the effective ways to improve the corrosion resistance of magnesium alloy. However, magnesium is very unstable in conventional electroplating bath. How to pretreat magnesium alloy surface and find out appropriate plating bath and electroplating process has become a hot research topic in this field. Therefore, this paper takes AZ91D magnesium alloy as the research object. The surface pretreatment and nickel plating process of AZ91D magnesium alloy were studied, and the corrosion resistance of the electroplated magnesium alloy was evaluated. The main research in this paper is as follows: 1) the pretreatment process of AZ91D magnesium alloy electroplating surface (acid pickling, activation, acid washing, activation). The results showed that the acid washing solution (242mL / L phosphoric acid / L concentrated nitric acid 12ml / L) prepared by this work had a good zinc dipping effect after 40 s acid washing (4 min activation, 15 min zinc dipping). Moreover, the removal of residual oxides on the surface of the sample and less pit erosion are beneficial to the deposition of the zinc dipping layer. It was found that the nickel electroplating process of AZ91D magnesium alloy was more uniform and its binding force was better than that of primary galvanizing. The nickel electroplating process of AZ91D magnesium alloy was studied. The effects of pulse electroplating and direct current nickel plating on nickel plating are compared. The results show that the efficiency of direct current electroplating is better than that of pulse electroplating. For pulse electroplating (pulse frequency 1000Hz current density is 1.25A / d m ~ (2), duty cycle is 20), electroplating efficiency is higher at 80 ~ (th). On the other hand, DC electroplating (current density 1.25A / dm2) and pulse electroplating (pulse frequency 1000Hz duty cycle 60% and 80% current-density 1.25A / dm2) can produce uniform nickel electroplating on the surface of AZ91D magnesium alloy, and direct current electroplating nickel has the best corrosion resistance. The adhesion between nickel coating and substrate is in accordance with the thermal shock test standard (ASTM B571-97Pu. 3). The process of electroplating copper-nickel composite coating on AZ91D magnesium alloy has been studied. In this paper, a formula of copper plating solution suitable for AZ91D magnesium alloy has been found out. The interface is tightly bonded by this formula. On the basis of this, nickel electroplating layer with uniform composition was prepared by pulse electroplating nickel (pulse frequency 1000Hz current density 2A / dm2 duty cycle 80) and direct current electroplating nickel plating (current density 2A / dm2). The corrosion resistance of the composite coating prepared by DC electroplating is better than that of pulsed electroplating. The nano hardness of nickel coating is 3.66 GPA, which is much higher than that of magnesium alloy substrate. The adhesion between copper and nickel coating meets the thermal shock test standard (ASTM B571-97).
【学位授予单位】：湘潭大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG174.44;TQ153.12

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