發(fā)布時(shí)間：2018-03-11 18:16

  本文選題：AZ31鎂合金　切入點(diǎn)：稀土Gd　出處：《太原理工大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：在資源和能源即將匱乏,環(huán)境污染不斷加重的今天,鎂合金由于其優(yōu)異的性能而得到了汽車行業(yè)、電子行業(yè)以及航空航天等行業(yè)的關(guān)注。但由于鎂合金較差的耐蝕性,使其在工業(yè)中的應(yīng)用受到了一定程度的限制。截至目前,雖然相關(guān)科研人員已對(duì)鎂合金的腐蝕與防護(hù)進(jìn)行了大量的研究,也取得了一定的成果,但由于對(duì)鎂合金腐蝕機(jī)制的認(rèn)識(shí)還不夠完善,致使其仍不能實(shí)現(xiàn)工業(yè)化的大規(guī)模應(yīng)用。本實(shí)驗(yàn)先在氬氣的保護(hù)下于井式電阻爐中精煉制備出不同Gd含量的4組AZ31鎂合金,而后利用OM,SEM,EDS以及XRD等檢測手段分析Gd的加入對(duì)合金相組成以及微觀組織的影響。在室溫和3.5%的中性Na_2SO_4溶液中進(jìn)行AZ31-xGd合金失重實(shí)驗(yàn)和電化學(xué)實(shí)驗(yàn)的同時(shí),對(duì)其在太原大氣環(huán)境中進(jìn)行大氣腐蝕實(shí)驗(yàn);待確定最佳稀土含量后,又研究了AZ31-4.12Gd合金在不同pH的Na_2SO_4溶液中的腐蝕行為。通過SEM觀察合金表面腐蝕產(chǎn)物去除前、后的形貌變化,用XRD分析腐蝕產(chǎn)物的相組成,研究Gd的添加對(duì)AZ31-xGd合金晶粒尺寸、第二相以及腐蝕速率的影響,并在此基礎(chǔ)上,進(jìn)一步分析了AZ31-4.12Gd合金在不同pH的Na_2SO_4溶液中的腐蝕行為,這為大幅度的提高鎂合金的耐蝕性以及擴(kuò)大鎂合金的應(yīng)用范圍提供了基礎(chǔ)的實(shí)驗(yàn)數(shù)據(jù)。本研究的結(jié)論如下:1.靜態(tài)失重實(shí)驗(yàn)中,隨Gd的增加,合金的腐蝕速率會(huì)明顯降低,尤其當(dāng)Gd的添加量為4.12%時(shí),合金的腐蝕速率最小,僅為0.675mg/(cm2.d-1),相比于未添加稀土Gd時(shí)的4.572mg/(cm2.d-1)下降了約85%。2.電化學(xué)實(shí)驗(yàn)中,Gd的加入在提高基體自腐蝕電位的同時(shí),降低了腐蝕過程中的電流密度。尤其當(dāng)Gd含量為4.12%時(shí),自腐蝕電位會(huì)由-1.6987V提高至-1.5966V,同時(shí)腐蝕電流密度則會(huì)由6.7372×10-4mA降低至2.9315×10-4mA。此外,阻抗譜的實(shí)驗(yàn)結(jié)果與極化曲線的實(shí)驗(yàn)結(jié)果有很好的一致性。3.Gd的添加,一方面細(xì)化了晶粒,降低了基體相與析出相之間的微電偶腐蝕;另一方面,改變了基體中第二相的數(shù)量與分布,起到了降低腐蝕電流密度的作用。同時(shí),新形成的Al2Gd相和固溶在基體中的Gd原子使基體表面形成了一層類似鍍層一樣的耐蝕保護(hù)膜,從而提高了合金的耐蝕性。4.AZ31-4.12Gd合金浸入不同pH的Na_2SO_4溶液中后,隨溶液pH值的增加,合金的腐蝕速率會(huì)不斷減小。此外,pH值的增加提高了基體的自腐蝕電位,降低了腐蝕過程中的電流密度,尤其當(dāng)溶液的pH值為12時(shí),合金的自腐蝕電位最大,同時(shí)腐蝕電流密度最小。這樣的結(jié)果表明合金的耐蝕性會(huì)隨溶液pH值的增大而增大。
[Abstract]:With the scarcity of resources and energy sources and the worsening of environmental pollution, magnesium alloys have attracted much attention from the automotive industry, electronics industry and aerospace industry because of their excellent performance. However, due to their poor corrosion resistance, The application of magnesium alloy in industry has been limited to a certain extent. Up to now, although the relevant researchers have done a lot of research on the corrosion and protection of magnesium alloy, some achievements have been made. However, the understanding of the corrosion mechanism of magnesium alloy is not perfect, so it can not realize the large-scale application of industrialization. In this experiment, four groups of AZ31 magnesium alloys with different Gd content were prepared by refining in well resistance furnace under the protection of argon gas. Then the influence of Gd addition on the phase composition and microstructure of the alloy was analyzed by OMS-SEMS-EDS and XRD. The weightlessness and electrochemical experiments of AZ31-xGd alloy were carried out at room temperature and in neutral Na_2SO_4 solution of 3.5% at the same time. After determining the optimum rare earth content, the corrosion behavior of AZ31-4.12Gd alloy in Na_2SO_4 solution with different pH was studied. The morphology changes before and after the removal of corrosion products on the surface of the alloy were observed by SEM. The phase composition of corrosion products was analyzed by XRD, and the effect of Gd addition on grain size, second phase and corrosion rate of AZ31-xGd alloy was studied. On the basis of this, the corrosion behavior of AZ31-4.12Gd alloy in different pH Na_2SO_4 solution was further analyzed. This provides the basic experimental data for greatly improving the corrosion resistance of magnesium alloys and expanding the scope of application of magnesium alloys. The conclusions of this study are as follows: 1. In static weightlessness experiments, the corrosion rate of the alloys decreases obviously with the increase of Gd. In particular, the corrosion rate of the alloy was the lowest when the addition of Gd was 4.12. The corrosion rate of the alloy was only 0.675 mg / m 路cm ~ (-2) 路d ~ (-1), which decreased by 850.2. the addition of Gd in the electrochemical experiment increased the self-corrosion potential of the substrate, compared with 4.572 mg / r 路cm ~ (-2) 路d ~ (-1) without adding rare earth Gd. When Gd content is 4.12, the corrosion potential increases from -1.6987V to -1.5966V, and the corrosion current density decreases from 6.7372 脳 10-4mA to 2.9315 脳 10-4mA. in addition, when Gd content is 4.12, the corrosion potential increases from -1.6987V to -1.5966V, and the corrosion current density decreases from 6.7372 脳 10-4mA to 2.9315 脳 10-4mA. The experimental results of impedance spectroscopy are in good agreement with the experimental results of polarization curves. 3. The addition of Gd not only refines the grain size and reduces the microgalvanic corrosion between the matrix phase and the precipitated phase, but also reduces the microgalvanic corrosion between the matrix phase and the precipitated phase. The number and distribution of the second phase in the substrate were changed, and the corrosion current density was decreased. Meanwhile, the newly formed Al2Gd phase and the Gd atom dissolved in the substrate resulted in the formation of a layer of corrosion resistant protective film similar to the coating on the substrate surface. The corrosion resistance of the alloy. 4.AZ31-4.12Gd alloy immersed in Na_2SO_4 solution with different pH value, the corrosion rate of the alloy will decrease with the increase of pH value of the solution, in addition, the increase of pH value increases the self-corrosion potential of the matrix. The corrosion current density is decreased, especially when the pH value of the solution is 12:00, the corrosion potential of the alloy is maximum and the corrosion current density is the lowest. The results show that the corrosion resistance of the alloy increases with the increase of the pH value of the solution.
【學(xué)位授予單位】：太原理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG178

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