镁合金表面镍基非晶态镀层制备工艺及其耐蚀性研究

发布时间：2018-07-25 19:18

【摘要】：镁合金具有密度小、比强度高、减震性好以及优异的防电磁、耐冲击、传热导电性和切削加工性,然而其耐腐蚀性差极大地限制了其在诸多工业领域的广泛应用。为了提高镁合金的耐腐蚀能力,本研究首先在镁合金基体表面预镀铜,进而化学镀Ni-Cu-P、Ni-W-P、Ni-Mo-P三种不同的镍基非晶态镀层,研究了 CuS04、Na2W04、Na2Mo04添加量对三种镀层的相组成、耐腐蚀性以及附着力等方面的影响。本文的主要研究内容及结果如下:(1)首先在镁合金表面直流预镀铜作为中间层,预镀铜表面呈细小胞状的形貌,厚度约为2～3μm,与镁合金基体之间没有明显的孔隙、裂纹等缺陷,既减小了镁合金表面直接化学镀镀层的难度,又提高了化学镀镀层与镁合金基体之间的附着力,从而提高了外层镀层的耐蚀性。(2)Ni-Cu-P、Ni-W-P、Ni-Mo-P三种镀层的表面均呈现大小不一的胞状组织,表面均相对平整、结构致密;三种镀层均与镁合金基体结合良好。(3)对于Ni-Cu-P镀层,当镀液中CuS04的添加量为0.8 g/L时,镀层中磷的质量分数为9.06%,铜的质量分数为4.50%,Ni-Cu-P镀层为非晶态结构。其极化曲线表明,Ni-Cu-P非晶态镀层的自腐蚀电位为-0.31 V,腐蚀电流为0.0039396 A/cm2;其阻抗谱表明,镀层具有最大的容抗弧半径和|Z|值;全浸泡实验中,CuS04添加量为0.8 g/L的Ni-Cu-P镀层腐蚀后的组织最完整,腐蚀速率最低。(4)对于Ni-W-P镀层,当镀液中Na2W04添加量为15 g/L,pH值为6.5时,镀层为非晶态结构,镀层中磷和钨的质量分数分别为9.63%和1.14%;其极化曲线及阻抗谱表明,Ni-W-P镀层的自腐蚀电位(-0.326 V)较镁合金基体有较大的提高,而腐蚀电流(0.0027105 A/cm2)则明显降低,并且镀层具有最大的容抗弧半径;浸泡实验结果表明,镀液中Na2W04添加量为15 g/L的Ni-W-P非晶态镀层腐蚀速率最低,耐腐蚀性最佳。(5)对于Ni-Mo-P镀层,当镀液中Na2MoO4的添加量为0.4 g/L,溶液pH为9.5时,镀层中钼的质量分数为9.76%,而磷的质量分数为9.29%;镀层为非晶态结构;其极化曲线和阻抗谱表明,Ni-Mo-P非晶态镀层的自腐蚀电位为-0.26 V,腐蚀电流为0.0087246 A/cm2,并且具有最大的容抗弧以及|Z|值;全浸泡实验结果表明,镀液中Na2MoO4添加量为0.4 g/L的Ni-Mo-P非晶态镀层耐腐蚀性最佳。
[Abstract]:Magnesium alloy has small density, high strength, good shock absorption and excellent anti electromagnetic, impact resistance, heat transfer conductivity and machinability. However, its poor corrosion resistance greatly restricts its wide application in many industrial fields. In order to improve the corrosion resistance of magnesium alloys, this study was first plated on the surface of magnesium alloy matrix. Three different nickel base amorphous coatings were plated with Ni-Cu-P, Ni-W-P, Ni-Mo-P. The effects of CuS04, Na2W04 and Na2Mo04 additions on the phase composition, corrosion resistance and adhesion of the three coatings were studied. The main contents and results of this paper are as follows: (1) first, the direct copper plating on the surface of magnesium alloy was used as the middle layer, and the surface of the pre plated copper was presented. The thin cell morphology, with a thickness of about 2~3 mu m, has no obvious pores and cracks between the magnesium alloy matrix and the magnesium alloy matrix, which not only reduces the difficulty of direct electroless plating on the surface of magnesium alloy, but also improves the adhesion between the electroless plating and the magnesium alloy matrix, thus improving the corrosion resistance of the coating of the outer layer. (2) three kinds of Ni-Cu-P, Ni-W-P, Ni-Mo-P. The surface of the coating is all different in size and size, the surface is relatively flat and the structure is compact. The three coatings are all well combined with the magnesium alloy matrix. (3) for Ni-Cu-P coating, when the amount of CuS04 in the plating bath is 0.8 g/L, the mass fraction of phosphorus in the coating is 9.06%, the mass fraction of copper is 4.50%, and the Ni-Cu-P coating is amorphous structure. The polarization curves show that the self corrosion potential of the Ni-Cu-P amorphous coating is -0.31 V and the corrosion current is 0.0039396 A/cm2, and the impedance spectrum shows that the coating has the maximum radii of tolerance arc and |Z| value. In the whole immersion experiment, the microstructure after the CuS04 addition of Ni-Cu-P coating with the amount of 0.8 g/L is the most complete, and the corrosion rate is the lowest. (4) for the Ni-W-P coating, when the coating is deposited, the corrosion rate is the lowest. When the addition of Na2W04 is 15 g/L and the pH value is 6.5, the coating is amorphous, and the mass fraction of phosphorus and tungsten in the coating is 9.63% and 1.14%, respectively. The polarization curves and impedance spectra show that the self corrosion potential (-0.326 V) of the Ni-W-P coating is higher than that of the magnesium alloy, and the corrosion current (0.0027105 A/cm2) decreases obviously and is plated. The layer has the largest radii of tolerance arc. The result of soaking experiment shows that the corrosion rate of Ni-W-P amorphous coating with Na2W04 adding amount of 15 g/L in the plating bath is the lowest, and the corrosion resistance is the best. (5) for Ni-Mo-P coating, when Na2MoO4 is added in the bath 0.4 g/L and pH is 9.5 in solution, the mass fraction of molybdenum in the coating is 9.76% and the mass fraction of phosphorus is 9.. 29%, the coating is amorphous, and its polarization curve and impedance spectrum indicate that the self corrosion potential of Ni-Mo-P amorphous coating is -0.26 V, corrosion current is 0.0087246 A/cm2, and it has the maximum tolerance arc and |Z| value. The result of full immersion experiment shows that Ni-Mo-P amorphous coating with Na2MoO4 addition of 0.4 g/L in the bath is the best corrosion resistance.
【学位授予单位】：西安科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG174.4

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