Research On Technique And Performance Of Ni-P-Al₂O₃ Electroless Plating Layer Treated By Pulsed Nd:YAG Laser

With the development of modern industrial technology,the demands for the excellent surface performance on key part increased extremely.Traditional treatment method cannot satisfy these requests.Therefore,the research of composite materials and compound technique represents a new direction for preparation of high-properties surface coatings.To strengthen the surface performance of carbon steel,The experiment sought to solve the problem of uneven surface coating in traditional laser processing and heat effect in matrix of traditional electroless composite plating,in this paper,an Nd:YAG pulsed laser as a source of heat to strengthen the Ni-P-Al₂O₃ composite coating to exert the advantages of electroless composite plating and pulsed laser surface hardening technology.The impaction of parameters to the quality of strengthen layer was researched by using different parameters to process the composite coating.A model of the relationship between pulse-laser parameters and the pattern of electroless deposit composite coatings by using a back propagation neural network,the optimization of process parameters were defined.Then scanning electron microscopy（SEM） was used to observe the morphologies of coating.X-ray diffraction（XRD） and X-ray energy dispersive spectroscopy（EDS） were employed to analyze the phase transformation,the Mechanism of grain refinement was discussed.The Hardening mechanism and abrasive resistance before and after laser processing were researched.The main conclusions are the follows:[1]The width and depth of Ni-P-Al₂O₃ composite coating increased with the rising of the current intensity,pulse width and pulse frequency,due to the increased absorption energy. The width and depth of Ni-P-Al₂O₃ composite coating decreased with the increase of scaning speed,because the absorption of energy decreased.A model of the relationship between pulse-laser parameters and the pattern of electroless deposit composite coatings （taking into account hardened width,depth） with a back propagation neural network.The model effectively predicted the appearance of composite coating to a±9.67%relative margin of error in depth and 7.56%in hardened width.[2]Optimization of process parameters:I:200～240A;T:2.1～2.3ms;f:21～23Hz;v: 450mm/min;Lap rate:30%.[3]After pulsed laser treatment,the microstructures of Ni-P-Al₂O₃ electroless composite coating from the surface to interior were:1～2μm secondary dendrite and spherical crystal, cellular-dendritic and cellular crystal,cellular crystal and columnar crystal in succession. Nano-Al₂O₃ was decomposed and new phases such as Al₅FeNi,FeNi and Fe_0.64Ni_0.36 formed.[4]Due to the rapid cooling during pulsed laser heating process and the existence of heterogeneous phase particles in coating,subcooling degree decreased,which lead to refinement of grains.[5]Due to dispersion and transformation strengthening in fusion zone,the micro-hardness of the hardened region is approximately 4.5 times higher than the matrix and the wear weight loss of Ni-P-Al₂O₃ hardened region is 14%of the matrix.