热处理对Ni-P合金镀层组织结构、显微硬度与耐蚀性能的影响

目前,有关热处理对Ni-P合金镀层组织结构与性能的影响研究不够深入。采用脉冲电沉积方法在Q235钢表面制备Ni-P合金镀层,并在200～500℃下进行热处理。利用X射线衍射仪分析镀层的相结构,用电化学极化曲线和扫描电子显微镜(SEM)对镀层在3.5%NaCl,10%HCl和10%H2SO4溶液中的腐蚀行为进行了研究。结果表明,提高热处理温度,Ni3P相的析出速度增大,Ni-P合金镀层的晶化时间减少,达到最高硬度所需的热处理时间相应缩短,镀层经300℃和400℃热处理后的最高硬度分别达到862.8 HV2N和887.4HV2 N;Ni-P合金镀层热处理晶化后,其耐蚀性能显著降低,在3种腐蚀介质中均发生点蚀。

Influence of Heat-Treatment on Microstructure,Hardness and Corrosion Resistance of Pulse Electroplated Ni-P Alloy Coating

Ni-P alloy coating was prepared on the surface of Q235 steel by pulse electroplating.As-plated Ni-P alloy coating was heat-treated in a temperature range of 200～500 ℃.The phase structure of the coating was analyzed by means of X-ray diffraction.The corrosion resistance of the coating in 3.5% NaCl,10% HCl and 10% H2SO4 solution was evaluated by measuring electrochemical polarization curves.The corroded surface of the alloy coating was observed using a scanning electron microscope.Results show that the precipitating rate of Ni3P phase increases with elevating heat-treatment temperature,and the time for crystallization as well as for reaching the maximum hardness of Ni-P coating is reduced therewith.The Ni-P alloy coating heat-treated at 300 ℃ and 400 ℃ possessed the maximum hardness of 862.8 HV2 N and 887.4 HV2 N respectively.However,heat-treatment significantly reduced the corrosion resistance of Ni-P alloy coating and led to the pitting of coating in the three kinds of corrosive mediums.