Deposition And Properties Of Ni-Mo-P Alloy Coating Plated By Electroless Plating On Substrate Of Aluminum Alloy

In this thesis, Ni-Mo-P alloy coating was deposited by electreless plating using acidic plating solution on the substrate of aluminum alloy. The effects of bath temperature and concentration of Na₂MoO₄ on the composition, structure, properties, such as microhardness, deposition rate and adhesion of the Ni-Mo-P alloy deposits were studied by Thermal Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive Spectrometer (EDS), X-Ray Fluorescence (XRF), Transmission Electron Microscope (TEM), X-ray Diffractometer (XRD), Differential Scanning Calorimetry (DSC) and Laser Confocal Scanning Microscope (LCSM). The influence of heat treatment temperature on the structure, microhardness and adhesion of the Ni-Mo-P alloy deposits were also discussed.The experimental results show that the Ni-Mo-P alloy coating could be obtained using the acidic plating solution in which the C6H5Na3O7·2H2O was used as the complex agent.XRF results indicate that the Mo contents and the deposition rate would be increased with the increase of MoO42- concentration, corresponding with the decrease of P contents in the bath solution. The key plating factors, bath temperature and the concentration of Na₂MoO₄ were around 90℃and in the range from 0.5 g/L to 0.6 g/L, respectively. It was found that the maximum deposition rate was 9.5μm/h, the maximum microhardness was 458.70 HV, the maximum adhesion was 30 N, the minimum surface roughness (Rz) was less than 3040 ? obtained at the bath temperature of 90℃, the Na₂MoO₄ concentration of 0.5 g/L.TEM results demonstrate that amorphous structure was the main structure of Ni-Mo-P alloy coating. The microstructure of as plated coatings would be changed from amorphous to nanocrystalline and mix-crystalline structure with the change of the Na₂MoO₄ concentration. After heat-treatment at differernt conditions, the structure of Ni-Mo-P alloy coating experience a series of transformations, such as structural relaxation, formation of Ni nanocrystal, bulk formation of Ni₃P nanoerystal, especially, the grain aggregation and growth of Ni and Ni₃P may be increased with the increase of heat treatment temperature. The adhesion strength of as-plated coating reaches its maximum value (40 N) after heat treatment at 300℃, 1 h. The microhardness determined at the conditions of 400℃and 1 h on the cross section and surface were about 15.12 GPa and 774.23 HV, respectively.