Study On Preparation And Properties Of Wear And Anti-corrosion Resisting Nano-composite Coatings On Mg,Al Alloy Surface

Due to their good performance,aluminum\magnesium and their light alloys are widely applied in virous industries,however,their disvantages,such as low hardness,poor wear resistance and corrosion resistance,are becoming more and more outstanding.A proper surface treatment can improve their properties to a large scale.Electroless plating method,chemical conversion film method,spraying method etc.are usually used to improve the properties of light alloys.Up to now,the nickel-phosphor binary alloy has been the most widely used matrix for composite coating,but a few literature have been reported that the effect of the third element on the properties of the electroless coating.In addition,there is a few studies fucus on the wear resistance and corrosion resistance at the same time by a simple sparying method.Therefore,in the present studies Ni-Co-P/TiN composite coatings and PPS-PTFE/SiO2 composite coatings were successfully prepared on aluminum\magnesium alloy substrates,it can largely enhance the wear and corrosion resistance of the light alloy.Then the morphology,composition,adhension,microhardness,water contact angle,wear and corrosion resistance of deposits were characterized by scanning electron microscopy,energy dispersive spectroscope,X-ray diffraction,automatic scratch instrument,Vickers hardometer,high speed reciprocating friction tester,drop meter optical contact angle meter and electrochemical workstation,respectively,and finally find out the effects of Co content and SiO2 content on the structures and perproties of the coatings.The main conclusions are listed as follows:(1)Ternary Ni-Co-P/TiN(20 nm)nanocomposite coatings with Co content in the range of 0-23 wt.% were successfully co-deposited on Al alloys by electroless plating.The results reveal that all the coatings have a compact and rough granular structure with sub-micro globules non-uniformly distributed on the surface.The grain size and the content of Ni and P decrease.(2)The micro-hardness,adhension force,friction coefficient,waer and corrosion resistance correspondingly enhance with the increase of Co content.Ternary Ni-Co23-P/TiN coating with high Co content hold the lowest wear rate and the best corrosion resistance.(3)PPS-PTFE/SiO2 composite coatings were successfully prepared on Al alloys by a simple sparying method with 0-4 g/l SiO2 content.From the SEM,we can see that protrusions distribute on the surface of the coatings.The protrusions contain lots of air hole,which can catch air and is benefit to make superhydrophobic surface.The water contact angle of PPS-PTFE coating is 150.3o,but with the increase of SiO2 content in the solution,the water contact angle of PPS-PTFE/SiO2 coatings descend.(4)The water contact angle of the coatings with SiO2 particles decline no so obvious after sand abrasion.It reveals that SiO2 particle has a positive effect on wear resistance.In addition,the corrosion potential of prepared coatings is more positive than pristine Al alloy and corrosion current density of prepared coatings reveals a negative shift than pristine Al alloy.It is reveals that hydrophobic PPS-PTFE/SiO2 coatings improve the corrosion resistance of Al substrate.(5)The PPS-PTFE/SiO2 composite coatings with SiO2 in the range of 0-4 g/l were successfully prepared on AZ31 Mg alloys by a simple spraying process.It is found that the micron-sized protrusions distribute on the surface of the coatings,and the fibrous-network structure of PTFE arranges on the protrusions.The water contact angles of the PPS-PTFE/SiO2(0-4 g/l)coating are in range of(152o-145.5o)±0.3o.The samples exhibit an excellent self-cleaning property.(6)The water contact angle of the unabraded and 10 m-abraded PPS-PTFE/ SiO2(4 g/l)composite coating on the sandpaper is 145.5o±0.3o and 142.5o±0.3o,respectively,implying the PPS-PTFE/SiO2 composite coating is a robust superhydrophobic one with good wear resistance.The Tafel and EIS results show that the corrosion potential of PPS-PTFE/ SiO2(4 g/l)composite coating(1.34 V)is higher than pristine AZ31 Mg alloy(-1.5 V)and the corrosion current destity PPS-PTFE/ SiO2(4 g/l)composite coating(5.37e-6 A/cm2)is lower than pristine AZ31 Mg alloy(1.10e-3 A/cm2),in addition,the Rs and Rp of PPS-PTFE/ SiO2(4 g/l)coating are higher than pristine AZ31 Mg alloy.In conclusion,the PPS-PTFE/SiO2 coatings show superior corrosion resistance in 3.5 wt.% NaCl solution to pristine AZ31 Mg alloy.