Preparation And Performance Characterization Of Micro Arc Oxidation + Electroless Copper Plating Composite Coatings On Aluminum Alloy

Alumina ceramic coating can be prepared on aluminum alloy by micro arc oxidation?MAO?.This coating is rough and porous,which can be coverd by the Cu coating obtained by using electroless copper plating technology,instead of the traditional zinc dipping transition layer.The microstructure and properties of the Al+MAO+Cu composite coating was characterized.The composite coating is expected to be applied in the field of the decoration or LED aluminum substrate.In this thesis,a traditional solution system,copper sulfate as the main salt and formaldehyde as the reducing agent,was used to prepare a Cu coating on the sensitized and activated MAO coated substrate by electroless copper plating.The properties of MAO+Cu composite coating could be improved by adjusting the surface morphology and composition of the MAO ceramic coating.XRD,XPS,SEM,EDS,and white light interference profilometers were used to characterize the structure,micromorphology,and composition of the MAO coating and MAO+Cu composite coating;the wear resistance of the substrate and MAO+Cu composite coating was measured using wear tester;The breakdown voltage and thermal conductivity of the MAO coating was measured by withstand voltage tester and thermal conductivity tester.The results show that,the Cu top coating could significantly reduce the roughness and specific surface area of the MAO coating.Among them,the MAO-450V+Cu composite coating has a roughness reduced from 2.85?m to 1.178?m compared with the MAO-450V coating.The specific surface area is reduced by 62.99%;the binding force of the composite coating reaches to the ISO level 1 standard,which is better than that of the traditional zinc+Cu composite coating;The average friction coefficient of the traditional zinc+Cu composite coating is 0.65,and the average friction coefficient of the MAO-500V+Cu composite coating is0.51.The wear scar depth of the MAO-450V+Cu and MAO-500V+Cu composite coatings was lower than that of the zinc+Cu composite coating.The thermal conductivity of the MAO-450V ceramic coating on aluminum ally can reach 26.11 W/m?K.The breakdown field strength of the MAO ceramic coating decreases with the increasing of voltage.Adding sodium stannate,sodium tungstate,titanium potassium oxalate,or sodium tetraborate to the electrolyte,the MAO coatings with Sn,W,Ti or B addition can be prepared.The high temperature and high pressure produced by the micro arc discharge make Sn O₃^2-change into Sn O₂,existing in the ceramic coating,which shows desert yellow colour.The surface hardness of the MAO-Ti ceramic coating can reach 693.3 HV_0.2/10;The order of the bonding strength of MAO+Cu composite coatings is:MAO-B+Cu>MAO-Sn+Cu>MAO-W+Cu>MAO-Ti+Cu;The MAO-B+Cu composite coating has the best wear resistance,after that is MAO-Sn+Cu composite coating.The MAO-W+Cu and MAO-Ti+Cu composite coatings is broken during the fiction,and the wear of MAO coating is aggravated by wear debris,and the depth of wear scar is increased obviously;the incorporation of B improves the compactness of the MAO coating,and increases its thermal conductivity to 27.635 W/m?K.The introduction of different N sources into the electrolyte can be used to prepare aluminum nitride-doped MAO ceramic coatings.The ceramic coating with the addition of aluminum nitride powder shows decreasing surface porosity and pore size.Nanoparticles mainly exist in the micropores and the molten region.The surface hardness of the ceramic coating increases to 640.7 HV_0.2/10,the thermal conductivity is 36.28 W/m?K,and the breakdown strength is 71.43 k V/mm;urea is added to the electrolyte to prepare aluminum nitride-doped MAO ceramic coating with a large number of micropores and large aperture,and its hardness and thermal conductivity are 582.8 HV_0.2/10and 36.96 W/m?K,respectively;Copper plating coatings decrease the roughness of MAO-Al N and MAO-Urea ceramic coatings.The bonding strength of the MAO-Urea+Cu composite coating is better than that of MAO-Al N+Cu composite coating;The MAO-Al N+Cu composite coating is severely worn during the friction,the copper-plated coating is worn out,and a large amount of fine wear debris accumulates in the wear scar,which fails to reduce wear.However,the MAO ceramic coating still protects the aluminum alloy substrate.Meanwhile,the wear mark of the composite coating is not obvious,and the Cu top coating is not worn out.This composite coating has an excellent wear resistance.