Research On Al₂O₃/Ni-P Electroless Composite Plating Technology On Ultralight Magnesium Lithium Alloy

In the 21st century,lightweight materials are gradually favored in various fields.as a typical commercial magnesium lithium alloy,LA141 has low density,good toughness and rigidity,making it one of the most attractive materials.However,LA141 has low surface hardness,poor corrosion resistance and wear resistance,so improving its surface protection is of great significance to its development.Al₂O₃/Ni-Pcomposite plating has been extensively studied due to its excellent comprehensive performance.Therefore,in this paper,Al₂O₃/Ni-P composite coating was prepared on the surface of LA141 magnesium-lithium alloy by chemical composite plating.The results of the research were as follows:?1?The optimal formula and process conditions of electroless Ni-P plating on the surface of LA141 magnesium-lithium alloy were determined by orthogonal test:main salt NiSO₄ 25g/L,reducing agent NaH₂PO₂ 20g/L,complexing agent C₆H₅Na₃O₇ 9g/L,buffering agent NH₄HF₂ 10g/L,HF12ml/L,stabilizer CH₄N₂S 2mg/L,small amount of ammonia water,bath temperature 85?,pH=6.4.?2?The surface of the electroless Ni-P layer of the LA141 magnesium-lithium alloy under the optimal process parameters was silver-white,the micromorphology was a typical cell structure,and the thickness was about 35?m.Compared with the substrate,the hardness of the coating was increased 389HV.The corrosion potential of the coating was shifted by 0.47V positively,the corrosion current density reduced by two orders of magnitude,the capacitive arc radius was significantly larger than the substrate,and the friction coefficient and wear scar width of the coating were smaller than the substrate.The results indicate that the performance of the coating was better than the substrate.?3?Based on the optimal Ni-P electroless plating process,using SDBS and PEG as dispersants,the Al₂O₃ in the plating solution was dispersed under ultrasonic conditions,the effects of different stirring speeds and nparticle loading on the Al₂O₃/Ni-P composite coating on the surface of LA141 magnesium-lithium alloy were studied.When the stirring speed was 600rpm and the amount was 6g/L,the composite coating nparticles had the best dispersibility.The microscopic morphology was mainly composed of amorphous Ni-P and Al₂O₃ nparticles.The thickness was 45?m.The hardness of the magnesium-lithium alloy composite coating reaches 780.4HV,the corrosion potential and the corrosion current reach-0.502V and 3.85×10^-55 A/cm²,respectively,the capacitance arc radius was the largest,and the friction coefficient is between 0.45 and 0.55,and the width of the wear scar was about 750?m,the wear mechanism was mainly adhesive wear.In addition,under this condition,the LA141magnesium-lithium alloy composite coating had the best bonding performance with the substrate.?4?By comparing the hardness,corrosion resistance and wear resistance,it was shown that the advantage of composite plating over single chemical plating was that it could improve the overall performance of the coating.Among them,the hardness was increased 380HV,the corrosion potential was shifted by 0.6V,and the corrosion current density was reduced by about 2.4 times.And the radius of the capacitive reactance arc increases significantly.At the same time,the friction coefficient and wear scar width of the composite coating were relatively reduced by 0.15 and 250?m,respectively.In addition,the thickness of the composite coating was increased by10?m,indicating that composite plating can improve the plating speed.