Study on Electroless Plating Ni-Co-P Alloy Protection Deposit of Sintered NdFeB Permanent Magnet Material
|School||Henan Polytechnic University|
|Course||Materials Processing Engineering|
|Keywords||Sintered NdFeB permanent magnet materials Electroless plating Ni-Co-P alloy Cellular substance Corrosion resistance Heat treatment Crystal transition|
Sintered NdFeB magnet N45-type chemical plating Ni-Co-P coating protection, designed to improve its corrosion resistance. Pre Organization dense carbon steel substrate, optimized pre-treatment process, the chemical bath recipe and plating process, and on this basis, a combination of solid chemical plating Ni-P substrate surface in porous magnet / Ni-Co-P alloy coating, organizational structure and properties of Ni-Co-P coating research. Sintered NdFeB permanent magnet materials pre-treatment process optimization results: electrolytic degreasing, the weak acid pickling activated alkaline pre-plated Ni-P plating bath temperature of 85 ° C, plating time of 20min. The optimization results of the electroless plating bath and the plating process is: complexing agent sodium citrate; stabilizer thiourea, a dose of Trace; metal ion concentration ratio ([Co 2 sup>] / [ Ni 2 sup> Co 2 sup>]) for 0.3 0 sup> .6; the pH value 1 sup> 0; plating temperature for 85 ℃. Organizational performance results of the electroless plating Ni-P/Ni-Co-P alloy coating on sintered NdFeB magnets Ni-P pre-coating and the substrate was indented, Ni-Co-P coating surface smooth, silvery white metallic luster, The porosity of the coating is almost zero, and closely combined with the pre-coating of Ni-P. With the increase of the bath pH value, Ni-Co-P coating structure from amorphous to crystalline transition. Metal ion concentration than in the 0.2 0 sup> .6 range when the coating structure are amorphous, when the metal ion concentration ratio increases to 0.8, Ni-Co-P plating structure by amorphous that microcrystalline crystalline changing trends. The surface of the coating composition, by the sizes of the cellular substance extracellular substance size of the increase of the concentration ratio of the metal ion, the surface of the coating becomes gradually smaller, but increases when the metal ion concentration ratio of 0.6, the size of the intracellular substance. EDS analysis shows that, with the increase in the ratio of the concentration of metal ions, coating the Co content increasing, while declining Ni and P content, and P elements tend to segregate to the junction of the intracellular and extracellular connected. The results show that the corrosion resistance of the Ni-Co-P plating, the metal ion concentration ratio of 0.3 coating acidproof best corrosion, while the metal ion concentration ratio of 0.6 coating alkali salt best corrosion. Electrochemical environments (corrosion medium for a 3.5% NaCl solution), the metal ion concentration ratio of 0.3 coating the best corrosion resistance. Ni-Co-P coating heat treatment results show that: the hardness with heat treatment temperature increases;, Ni-Co-P coating crystalline transition occurs when the temperature of 400 ° C, and precipitation of a new phase of Ni 12 < / sub> P 5 , and the hardness of the peak; When the temperature rises to 500 ° C, the metastable phase Ni 12 P 5 into Ni 3 P-phase crystal transition completed hardness worse; continues to rise with the heat treatment temperature, Ni 3 P phase continued to gather coarsening, hardness declining The cellular morphology of Ni-Co-P coating surface into a worm-like morphology.