Electroless Plating Study On The Inner Wall Of Brass Capillaries

Due to its excellent machinability,electrical and thermal conductivity,the brass capillaries were widely used in the fields of the electronic information,thermal power and ships.However,the insufficiency of corrosion resistance and abrasion resistance limits its service life and application range.Here we report an electroless plating process for the preparation of wear-resistant and corrosion-resistant nickel alloy coatings on the inner wall of H62 brass tubes with an aspect ratio of 100.Since the properties of the in the tube coating are difficult to be characterized,the H62 brass plate was used as the substrate in the initial exploration process.Morphological and structure,hardness and corrosion resistance of the coatings were studied by means of X-ray diffractometer（XRD）,scanning electron microscopy（SEM）,microhardness tester and electrochemical workstation.Firstly,a combination of single-factor experiment and orthogonal test was applied to explore the influence of various process conditions on the plating layer,and the optimal medium temperature alkaline chemical nickel plating process was obtained;then,Ni-W-P plating layer was prepared by adding different concentrations of Na₂WO₄to the plating solution,and the optimal amount of Na₂WO₄ was determined.The effects of different heat treatment processes on the plating properties were investigated;finally,the inner wall of H62 brass capillaries were plated by the chemical Ni-W-P plating technique,and the influence of the variation of the plating solution flow rate on the morphology,deposition rate and thickness uniformity of the plating layer was explored,and the main conclusions are as follows.The best process parameters for medium temperature alkaline chemical plating on H62 brass plate are:Ni SO₄?6H₂O 25 g/L,Na H₂PO₂ 29 g/L,C₆H₅Na₃O₇ 20 g/L,C₃H₆O₃2 m L/L,NH₄Cl 15 g/L,KIO₃ 10.5 mg/L,the bath temperature is 65°C and the p H is 8.6.The coating obtained by this process has excellent surface quality,the hardness is 436.35HV,which is 3.2 times that of the brass substrate,and the self-corrosion current density is 4.631×10^-6 A/cm²,which is 50%lower than that of brass.Under Ni-P process conditions,the addition of different concentrations of sodium tungstate produces W elements in the plating,which reduces P elements and their crystallinity is improved.The study found that in 40 g/L sodium tungstate solution,the coating performance was the best,the hardness reached 622.5 HV,the self-corrosion potential was-0.344 V,and the self-corrosion current density was 1.124×10^-6 A/cm².The resistance is 39397Ω·cm².The as-plated coating was kept at 400°C for 1 h to improve the wear resistance of the coating.The average friction coefficient was 0.4353,which was30%lower than that of the as-plated coating.4.44×10^-5 g/m,a decrease of 67%.The best electroless Ni-W-P process was used to prepare the coating on the inner wall of this brass tube,and the deposition rate and uniformity of the coating were compared.,is 7.37μm/h,the P element content is 2.16 wt%,the W element content is1.76 wt%,and the average thickness deviation is moderate,which is 9%.In this study,the Ni-W-P coating produced by the electroplating process on the inner wall of H62 brass capillaries with an L/D ratio of 100 can enhance the corrosion and wear resistance of the body,which is a more desirable surface treatment technology for the inner wall of capillary.