Electroless Ni-P-MoS₂Composite Coating On7075/2024Aluminum Alloy And The Effect Of Plating Parameters On The Properties Of Coating

The scientists have payed more attention to Aluminium and aluminium alloy, due totheir outstanding properties, for example, low density, high strength and so on. It hasbecome one of the extensive use of the materials in the industrial production. However,because of their low surface hardness, wear resistance and limit the further application ofaluminum and aluminum alloys. Electroless Ni-P-MoS2is a commonly used metalsurface treatment technology，it can keep advantages of aluminum(low density, highstrength, etc), also have a good wear resistance to the surface, it is one of the mosteffective ways to change the aluminum alloy surface wear resistance.In order to improve the wear resistance of7075/2024aluminum alloy surfaces,Ni-P-MoS2composite coating was electrolessly deposited onto7075/2024aluminumalloy, the influences of MoS2concentration, surface active agent concentration, pH,temperature and deposition time on the deposition rate were studied to determine theoptimum process parameters, XRD，SEM were used to investigate the phase structure,morphology and composition. In order to further improve the wear resistanceperformance of composite coating, for Ni-P-MoS2composite coating by laser treatment,analyze the impact of laser treatment on the wear resistance of composite coatings bycomparing before and after laser treatment composite coating erosive wear SEM pictures.1. The optimum process parameters of electroless Ni-P-MoS2composite coating on7075/2024aluminum alloy are that nickel salt is15g/L, surface active agent is0.2g/L,MoS2concentration is14g/L,pH value is5.5, temperature is80°C and deposition time is1.5h. XRD, SEM, hardness testing observations revealed that the combination of thecoating and substrate is good, with good surface morphology.2. Under the load of10N, the wear of time is5min, the concentration of MoS2on theeffect of the composite coating wear weightlessness was studied. The result showed that the amount of Ni-P-MoS2composite coating wear is reduced gradually with the increasedconcentration of MoS2.When the concentration of MoS2is16g/L, the amount of7075and2024aluminum alloy aluminum composite coating wear reached1.8mg and2.5mg. Theexperiment of friction coefficient shows that the friction coefficient of composite coatingdecreases with the increased concentration of MoS2.The coefficient of friction of7075aluminum alloy composite coating reduce from0.34(the concentration of MoS2:8g/L) to0.18(the concentration of MoS2:16g/L).The coefficient of friction of2024aluminumalloy composite coating reduce from0.33(the concentration of MoS2:8g/L) to0.16(theconcentration of MoS2:16g/L).3. Laser melting on composite coating obtained under optimum composition andoptimal parameters (laser power:1500w, scanning speed:13mm/s), XRD and SEM teston the coating of after laser melting treatment. The results show that coating of grainrefinement and Ni3P, Ni12P5strengthening phase appeared in the diffraction pattern of thecoating after laser melting, these strengthening phases improved wear resistance of thecoating. The diffraction peaks of MoNi4appeared in the diffraction pattern of7075aluminum alloy composite coating, maybe some of MoS2is melted by high temperaturesand they form a compound with Ni-P during the laser melting process.4. Laser melting treatment improves the wear resistance of the coating. The weartests show that the amount of wear of7075/2024aluminum alloy composite coating afterlaser melting process is less than the amount of coating without melted coating. Lasermelting treatment reduced the coating surface roughness and the friction coefficient ofcoating is also decreases.