柠檬酸体系电沉积Ni-Cr合金镀层工艺影响因素分析

Analysis of Factors Influencing the Electrodeposited Process of Ni-Cr Alloy Coatings in Citric Acid Bath

为了提高铝材的耐蚀性和表面硬度,用柠檬酸体系在铝基体上制备了Ni-Cr合金镀层。研究了工艺参数对镀层组成、形貌和结构的影响,确定了最佳工艺条件。结果表明:最佳工艺条件获得的镀层光亮、平滑,显示出密集的球形细粒状形貌特征;镀层为面心立方(FCC)Ni-Cr固溶体纳米晶结构;适当降低温度,增大电流密度,提高镀液中CrCl3浓度,有利于镀层表面合金颗粒细化和晶体粒径的减小,晶体结构有序性增强;随着pH值升高,镀层颗粒细化,晶型改善,当pH值大于3时,镀层晶体粒径逐渐变粗,内应力增大,表面形貌变差。随着Cr含量增大,镀层表面粒径减小,晶界延长,镀层耐蚀性提高;镀层与Al基体结合良好。

Ni-Cr alloy coatings were prepared on the surface of aluminum substrates by electrodeposition in citric acid bath so as to improve the corrosion resistance and increase the surface hardness of aluminum.The influences of electrodeposition parameters on the composition,morphology and microstructure of the coatings were investigated,and the optimum process conditions were determined.Results show that the Ni-Cr alloy coating obtained under the optimized electrodeposition condition is bright and smooth,showing morphology of compact spherical fine grains.The coatings consisted of face-centered cubic(FCC) Ni-Cr solid solution nanocrystallines.Lowering temperature,increasing current density and increasing concentration of CrCl3 appropriately were beneficial to the refinement of grains and enhancement of crystalline orderliness.Besides,increasing pH value also contributed to refined grains and improved crystalline pattern of the alloy coatings.However,the Ni-Cr alloy coating obtained at a pH value of above 3 was coarsened and had an increased internal stress and surface roughness.Moreover,the grain sizes of the alloy coatings decreased and the grain boundaries propagated with increasing Cr contents,accompanied by increased corrosion resistance therewith.The coatings were well adhered to the Al substrates.