本文選題：AZ91D鎂合金　切入點(diǎn)：重復(fù)浸鋅　出處：《湘潭大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：鎂合金具有低密度、高比強(qiáng)度、高比剛度以及良好的導(dǎo)電性能和電磁屏蔽性能等優(yōu)點(diǎn),在航空航天、汽車和電子工業(yè)等領(lǐng)域有廣闊的應(yīng)用前景,但鎂合金較差的耐蝕性能是限制其實(shí)際應(yīng)用的主要因素之一。電鍍方法是提高鎂合金耐蝕性能的有效途徑之一,然而鎂在常規(guī)的電鍍液中極不穩(wěn)定。如何對(duì)鎂合金表面進(jìn)行預(yù)處理并找出合適的鍍液和電鍍工藝成為當(dāng)前該領(lǐng)域的研究熱點(diǎn)。因此,本論文以AZ91D鎂合金為研究對(duì)象,開(kāi)展了鎂合金表面預(yù)處理及電鍍鎳工藝研究,同時(shí)對(duì)電鍍后鎂合金的耐蝕性能進(jìn)行了評(píng)估。本文的主要研究如下:(1)對(duì)AZ91D鎂合金電鍍表面預(yù)處理工藝(酸洗、活化、浸鋅等工藝)進(jìn)行了研究,結(jié)果表明,經(jīng)本工作配制的酸洗液(磷酸242mL/L+濃硝酸12mL/L)酸洗40s后進(jìn)行活化浸鋅(活化4min、浸鋅15min)后得良好的浸鋅效果,且(酸洗活化后)樣品表面殘余氧化物的去除以及更少的坑蝕有利于浸鋅層的沉積,進(jìn)一步研究發(fā)現(xiàn)重復(fù)浸鋅后再進(jìn)行電鍍鎳制備的電鍍鎳層成分均一且其結(jié)合力優(yōu)于一次浸鋅。(2)對(duì)AZ91D鎂合金電鍍鎳工藝進(jìn)行了研究,對(duì)比分析了脈沖電鍍鎳工藝和直流電鍍鎳工藝對(duì)鍍鎳層的影響。結(jié)果表明,采用直流電鍍的電鍍效率優(yōu)于脈沖電鍍,而對(duì)于脈沖電鍍(脈沖頻率1000Hz+電流密度為1.25A/dm2),占空比為20%、80%時(shí)電鍍效率較高,而直流電鍍(電流密度為1.25A/dm2)以及脈沖電鍍(脈沖頻率1000Hz+占空比為60%和80%+電流密度為1.25A/dm2)均可在AZ91D鎂合金表面制備出成分均一的電鍍鎳層,直流電鍍鎳所得鍍鎳層耐蝕性能最好,且鎳鍍層與基體結(jié)合力均符合熱震測(cè)試標(biāo)準(zhǔn)(美國(guó)材料協(xié)會(huì)標(biāo)準(zhǔn)ASTM B571-97)。(3)對(duì)AZ91D鎂合金電鍍銅鎳復(fù)合鍍層的工藝進(jìn)行了研究,本文找出了一種適用AZ91D鎂合金的電鍍銅鍍液配方,并采用該配方制備出了界面結(jié)合緊密、覆蓋良好的銅鍍層。在此基礎(chǔ)上采用脈沖電鍍鎳(脈沖頻率1000Hz+電流密度為2A/dm2+占空比80%)和直流電鍍鎳(電流密度為2A/dm2)均制備出成分均一的電鍍鎳層,其中直流電鍍制備的復(fù)合鍍層的耐蝕性能優(yōu)于脈沖電鍍鍍層,鎳鍍層納米硬度達(dá)3.66GPa遠(yuǎn)高于鎂合金基體,銅鎳鍍層與基體結(jié)合力均符合熱震測(cè)試標(biāo)準(zhǔn)(美國(guó)材料協(xié)會(huì)標(biāo)準(zhǔn)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).
【學(xué)位授予單位】：湘潭大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG174.44;TQ153.12

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