Study On Ni-P-MWNTs Composite Coating On Magnesium Alloy At Medium Temperature And Its Coating Properties

Magnesium alloy has many advantages such as low density,high specific strength,good heat dissipation and so on,making it widely used in automobile,communication,electronics and aerospace.However,the poor corrosion resistance of magnesium alloys restricts its application in the field of practice.Chemical plating on the surface of magnesium alloy by electroless plating has become a hot spot in the study of the surface treatment of magnesium alloys.In this thesis,AZ31 magnesium alloy is used as the experimental material.In view of the problems existing in the electroless plating process of magnesium alloy,the Ni-P-MWNTs composite plating on the matrix of AZ31magnesium alloy was carried out,and the influence of the process parameters on the composite coating is discussed.The surface morphology and properties of the electroless plating of magnesium alloy were analyzed by scanning electron microscope（SEM）,X ray diffractometer（XRD）and electrochemical workstation.The theoretical basis was added to the functional composite plating on magnesium alloy by electroless plating,which provided reference basis for the production practice,improved the properties of magnesium alloy and widened the use range of magnesium alloy.The main results are as follows:1)The work systematically studied the effect of chemical bath concentration and process conditions on the electroless plating process on AZ31 magnesium alloy.The optimum technological conditions for the electroless plating of AZ31 magnesium alloy Ni-P alloy are:NiSO₄·6H₂O 18g·L^-1,NaH₂PO₂·H₂O 22g·L^-1,C₆H₈O₇·H₂O 9g·L^-1,NH₄HF₂ 20g·L^-1,pH:6.4,temperature:82℃,HF（40%）10ml·L^-1,Thiourea:1mg·L^-1。2)Modified MWNTs was added to the electroless plating solution to form a chemical composite plating solution that could be stable in a certain time.The synergistic effect of the content of MWNTs in the plating bath and the MWNTs content in the coating of DTAB/MWNTs was studied.When the concentration of MWNTs in the solution is 1.2 g/L and DTAB/MWNTs is 1,the maximum value of MWNTs in the coating is reached,and the mass ratio is about 2.5wt%.3)Chemical composite coating of magnesium alloy is bright black,smooth and uniform surface and uniform particles on the surface of the coating.According to the X ray diffraction test,the carbon nanotubes have been embedded in the coating,and the MWNTs particles are evenly distributed,and there is no obvious pore defect and tight binding.The calculation speed 12¹4μm·h^-1 plating coating;good adhesion with the substrate.4)the Ni-P-MWNTs composite coating on AZ31 magnesium alloy has a good anticorrosion effect on magnesium alloy.The self corrosion potential of AZ31 magnesium alloy matrix is-1.36 V,and the self corrosion potential of Ni-P-MWNTs composite coating is about-0.49 V,and the passivation interval is about 300 mV when the dynamic potential scan enters the anode region.Compared with magnesium alloy substrate,Ni-P-MWNTs composite coating can play a good role in corrosion protection for magnesium alloy substrate.5)the friction and wear test method was used to study the friction properties of Ni-P coating and Ni-P-MWNTs composite coating on magnesium alloy.It is found that the composite entry of solid lubricant MWNTs can significantly reduce the friction coefficient of the coating.The absolute value and variation of the friction coefficient of the Ni-P coating are larger than that of the Ni-P-MWNTs coating,and the friction coefficient of the Ni-P-MWNTs coating is basically guaranteed with the prolongation of the time.Holding constant.The composite MWNTs particles play a significant role in lubrication and antifriction.The composite of MWNTs particles can improve the lubricity of the electroless coating and reduce the wear rate of the coating to a certain extent.