【摘要】 采用功能性复合镀层是解决镁合金耐蚀性差的重要方法,可有效扩展镁合金的用途,初始沉积机理的研究对复合镀工艺的优化设计具有重要意义。采用金相观察(OM)、扫描电子显微镜(SEM)、能谱(EDS)等方法研究了铸态AZ70镁合金化学复合镀Ni-P-纳米TiO2合金的初始沉积特点。结果表明:因为镁合金不具有催化活性,镍的初始沉积过程分为3个阶段:最先是电化学机制占主导地位,是由于镁合金中β相和α相存在电位差,在镀液中形成了微型原电池所引起;其次是电化学机制和次磷酸盐的还原作用机制并存,并由电化学机制占主导地位逐步过渡到以次磷酸盐的还原作用机制占主导地位;最后,当施镀50s左右时,则完全转为次磷酸盐的还原作用机制。纳米TiO2粒子的沉积过程相对简单,分为2个阶段:最先TiO2粒子由于电化学吸引择优在α相上沉积,施镀50s左右,当基体被复合镀层覆盖后,TiO2粒子的沉积没有位置取向。更多还原

【Abstract】 The initial deposition mechanism of electroless Ni-P/nano-TiO2 composite coating on as-cast AZ70 alloy was investigated by means of opti-cal microscopy,scanning electron microscopy,and energy disper-sive spectrometry.Results show that the deposition process of Ni on Mg alloy without catalytic activity can be divided into three steps.At first,electrochemical reaction dominated the initial deposition process,due to the formation of galvanic cell with the plating solution in the presence of the potential difference of β(Mg17Al12)phase and α(Mg)phase.Secondly,the reduction of hypophosphite and electrochemical reaction coexisted,and the electrochemical reaction was gradually taken advantage by the re-duction of hypophosphite.Finally,at a plating time of about 50 s,the deposition of Ni was solely controlled by the reduction of hypophosphite.Moreover,the co-deposition of nano-TiO2 parti-cles was relatively simple and could be divided into two steps.Namely,nano-TiO2 particles initially preferentially deposited on α phase,owing to the galvano-chemical adsorption.Then,when the plating time approached about 50 s and the metal matrix was covered with the composite coating,the deposition of nano-TiO2 particles became random.更多还原