添加剂对AZ31表面化学镀Ni-P膜性能影响的研究

发布时间：2018-12-12 15:37

【摘要】：化学镀的镀层在均匀性、耐蚀性、硬度、可焊性、磁性和装饰性等性能都显示出优越性。作为一种优良的表面处理工艺，已被广泛应用于多个领域，比如军用器材、铸模、模具、航空、纺织、食品及木材加工机械的表面强化。在实际的工业生产中，为了兼顾Ni-P膜层的镀膜速率、物理和化学等综合性能，往往在镀液中添加多种组分，比如第二主盐、添加剂、纳米无机盐颗粒。有些还对所得的Ni-P膜层进行热处理，以上的改善方式使镀液成分变得复杂，使生产和后处理成本提高。本论文以热轧态AZ31镁合金为研究对象，利用化学镀法在其表面沉积Ni-P膜层。通过在镀液中添加不同浓度的添加剂，研究其对化学镀Ni-P膜层的耐蚀性、显微硬度、干摩擦系数等力学性能的影响。用X射线粉末衍射仪(XRD)、扫描电子显微镜(SEM)、能谱分析(EDS)、显微硬度仪、高温圆盘磨损仪、电化学工作站等仪器对所沉积的Ni-P膜层的成分、形貌、晶粒尺寸，，膜层硬度，耐磨性及耐蚀性能进行了表征分析。得到的结论如下： (1)当糖精钠的浓度从0g/L增加到5g/L，SEM显示所得Ni-P膜层的晶粒尺寸和膜层的厚度是逐渐减少的，孔隙的数量是先减少后增加；EDS数据显示磷的含量也是逐渐降低的(其含量都大于7wt.%，属于高磷膜层)。极化曲线及阻抗图谱显示2g/L糖精钠的镀液中所得膜层在3.5%NaCl溶液的耐腐蚀性最好。并对2g/L糖精钠浓度的镀液中所沉积的Ni-P膜层的形成机理做了详细的研究，发现其由两步反应组成：第一步是Ni离子与镁合金基体之间的置换反应，第二步是镍与磷的共沉积反应。显微硬度数据发现Ni-P膜层硬度随糖精钠的浓度增加呈现一个上升的趋势。当糖精钠的浓度为5g/L，膜层的显微硬度值达到1003.7HV0.025。Ni-P膜层与不同的摩擦副摩擦体现出不同的摩擦机理：与GCrl5摩擦副摩擦表现为轻微切削磨损机理；与Al2O3摩擦副摩擦表现出粘着磨损机理。而且膜层通过与不同摩擦副的磨损实验显示：Ni-P磨层的失重、磨痕的宽度及摩擦系数随糖精钠的浓度增加而变小,说明随着镀液中糖精钠浓度的增加Ni-P膜层耐磨性是逐渐增加的。 (2)当聚乙烯吡咯烷酮(PVP)的浓度从8g/L增加到12g/L，XRD和EDS数据显示膜层由结晶性较好的Ni单晶和结晶性差的Ni-P组成。SEM显示所得Ni-P膜层的厚度是增加后减少。极化曲线及阻抗图谱显示10g/L聚乙烯吡咯烷酮的镀液中所得Ni-P膜层在3.5%NaCl溶液的耐腐蚀性最好。极化曲线有个极小的自腐蚀电流密度(1.29μA/cm2)和高的极化电阻(73581Ωcm2)，说明此膜层展现较好的耐蚀性。
[Abstract]:The electroless plating shows advantages in uniformity, corrosion resistance, hardness, solderability, magnetism and decoration. As an excellent surface treatment technology, it has been widely used in many fields, such as military equipment, mold, aviation, textile, food and wood processing machinery surface strengthening. In practical industrial production, in order to take account of the coating rate, physical and chemical properties of Ni-P film, many components such as second main salt, additive and nano-inorganic salt particles are often added to the bath. Some of the obtained Ni-P films are heat-treated, and the above improvements make the composition of the bath become more complicated, and the production and post-treatment costs are increased. In this paper, hot rolled AZ31 magnesium alloy was used to deposit Ni-P film on its surface by electroless plating. The effects of additives of different concentrations on the corrosion resistance, microhardness and dry friction coefficient of electroless Ni-P coating were studied. X-ray powder diffractometer (XRD),) scanning electron microscope (SEM),) was used to analyze the composition, morphology and grain size of Ni-P film deposited by (EDS), microhardness tester, high temperature disc wear tester and electrochemical workstation. The hardness, wear resistance and corrosion resistance of the film were characterized and analyzed. The conclusions are as follows: (1) when the concentration of sodium saccharin increases from 0g/L to 5 g / L SEM, the grain size and thickness of the Ni-P film decrease gradually, and the number of pores decreases first and then increases; The EDS data showed that the phosphorus content decreased gradually (the contents were higher than 7 wt. and belong to the high phosphorus film). Polarization curves and impedance spectra showed that the coating obtained in the solution of 2g/L saccharin sodium had the best corrosion resistance in 3.5%NaCl solution. The formation mechanism of the Ni-P film deposited in the bath of 2g/L saccharin sodium concentration was studied in detail. It was found that the formation mechanism of the Ni-P film was composed of two steps: the first step was the replacement reaction between Ni ion and magnesium alloy substrate. The second step is the codeposition of nickel and phosphorus. Microhardness data show that the hardness of Ni-P film increases with the concentration of saccharin sodium. When the concentration of sodium saccharin is 5 g / L, the microhardness of the film reaches to different friction mechanism of 1003.7HV0.025.Ni-P film and different friction pairs. The friction mechanism of GCrl5 friction pair is slight cutting wear mechanism. Friction with Al2O3 friction pair shows adhesive wear mechanism. Moreover, the wear experiments with different friction pairs showed that the weight loss, wear mark width and friction coefficient of Ni-P wear layer decreased with the increase of saccharin sodium concentration. The results show that the wear resistance of Ni-P film increases with the increase of concentration of saccharin sodium in the plating solution. (2) when the concentration of polyvinylpyrrolidone (PVP) increased from 8g/L to 12 g / L, XRD and EDS data show that the film is composed of Ni single crystal with good crystallinity and Ni-P with poor crystallinity. SEM shows that the thickness of Ni-P film increases and then decreases. Polarization curves and impedance spectra showed that the Ni-P film obtained from 10g/L polyvinylpyrrolidone plating solution had the best corrosion resistance in 3.5%NaCl solution. The polarization curve has a minimal corrosion current density (1.29 渭 A/cm2) and a high polarization resistance (73581 惟 cm2), which indicates that the film exhibits good corrosion resistance.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG174.4

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