Research On Corrosion And Wear Resistance Coating Of AZ91 Alloy Surface For Vehicle

As a metal structural material with light weight and high specific strength,magnesium alloy has great application prospects in the field of automobile lightweight.However,the lack of corrosion resistance and wear resistance of magnesium alloys limits its practical application.In this paper,micro-arc oxidation technology is used to prepare MAO coating on the surface of AZ91 alloy,and the optimal addition amount of aluminate or tungstate in the electrolyte and its influence on the micro-arc oxidation process are explored.In order to further improve the corrosion resistance and wear resistance of the MAO coating,ZrSiO₄particles were added to the electrolyte,and a micro-arc oxidation coating with good sealing performance was prepared by a one-step sealing method.The micro-arc oxidation and self-assembly technology are combined to prepare a micro-arc oxidation/hexadecyltrimethoxysilane(MAO/PHTDMS)composite coating,and the formation and corrosion mechanism of the composite coating are explored.Research indicates:(1)?The MAO coating prepared by adding aluminate or tungstate to the silicate-phosphate composite electrolyte is mainly composed of Mg O,Mg Al₂O₄,Mg₂SiO₄,Al₂O₃,Al PO₄,Mg₃(PO₄)₂,and promotes the hard phase Mg Al₂O₄and WO₃.With the increase in the amount of addition,the thickness of the coating is greatly increased,and the density and hardness are improved.At 2 g/L,the best corrosion resistance and wear resistance are achieved at the same time,but the overall improvement effect of tungstate is less than that of aluminate.(2)?The ZrSiO₄particles added in the electrolyte are directly diffused and adsorbed into the pores of the MAO coating to seal and increase the thickness,the thickness of the coating increases from about 16?m to about25?m;Part of the ZrSiO₄particles decomposed into ZrO₂and SiO₂particles during the micro-arc oxidation process,among them,the ceramic toughening phase ZrO₂can reduce the formation of micro-cracks and other defects in the film.The MAO coating prepared by adding 15 g/L ZrSiO₄to the electrolyte obtained the best sealing effect,while significantly increasing the hardness of the film(increased by 100.94 Hv)and lowered the Young's modulus(decreased by 484 MPa),to obtain the best corrosion resistance(the self-corrosion current is reduced by three orders of magnitude)and wear resistance(the friction coefficient is reduced to0.162).(3)?Treat the AZ91 alloy with MAO coating in a solution consisting of NaOH and EDTA-2Na at 90?for 1 h,and then immerse it in polyhexadecyltrimethoxysilane for 1 h to obtain a MAO/PHTDMS composite coating.The PHTDMS coating is uniform and compact,the pores disappeared,the thickness is appropriate(about 14?m),and it is not easy to crack,the water contact angle increases from 20.4°to 120.2°,forming a hydrophobic surface,the self-corrosion current decreases by two orders of magnitude,and the polarization resistance increases three orders of magnitude.