材料期刊网

    主要研究了酸洗和超声波清洗前处理工艺对化学镀镍结合力的影响.扫描电镜(SEM)结果表明：随着硝酸浓度的增加，烧结钕铁硼酸洗后表面越来越粗糙.其中，硝酸(65％)浓度为20~40 ml/L时，酸洗不能完全去除烧结钕铁硼表面的氧化膜；硝酸(65％)浓度为80~100 ml/L时，不仅将钕铁硼表面的氧化物和富钕相腐蚀掉，而且腐蚀钕铁硼内部的富钕相，使钕铁硼表面粉化.酸洗后，烧结钕铁硼表面粘有大量脱落的主相的晶粒，使用超声波可以有效地去除这些晶粒，消除钕铁硼和镀层之间的夹层.万能实验拉伸机实验结果表明：当硝酸(65％)浓度为60 ml/L，酸洗时间40 s，并结合超声波清洗时，得到了化学镀镍层结合力最好，结合力大于28 MPa.

    As it is well recognized that pretreatment is a key procedure for reaching a proper adhesion of an electroless Ni-P coating on a substrate of sintered Nd-Fe-B permanent magnet.In this respect,the effect of pretreatments of acidic cleaning and ultrasonic rinsing on the adhesion of electroless Ni-P coating was studied.SEM observation reveals that the surface morphology of magnet became much coarser with the increasing of nitric acid concentration in the pickles.When the pickles with 20~40 ml/L nitric acid,the oxide scale on the magnet may not be removed.However when the pickles with 80~100 ml/L nitric acid,not only the oxide scale and Ndrich phase on the surface,but also the Nd-rich phase deep in the magnet could be removed,which made the magnet pulverized.After acidic cleaning,lots of Nd₂Fe₁₄B grains on the surface were separated from the magnet.Ultrasonic rinsing could effectively remove the Nd₂Fe₁₄B grains,which might be helpful for higher adhesion of electroless plated Ni-P coatings.So with ultrasonic rinsing,the optimized pretreatment process was that the concentration of nitric acid was 60 ml/L for the pickles with an acidic cleaning time 40 s.By this process,the adhesion strength of the electroless Ni-P coating with the substrate of sintered Nd-Fe-B permanent magnet may reach over 28 MPa.