Preparation And Performance Study Of Environmentally Friendly Low Contact Resistance-Corrosion Resistance Conversion Film For Aluminum Alloy

With the rapid development of electronic information technology,people are enjoying an efficient and convenient life.However,they also face the problem of electromagnetic interference（EMI）,which cannot be ignored.EMI has become a new source of pollution that threatens human health.In this context,aluminum alloy,known for its excellent overall performance,is widely used in the field of communication and electronics.Nevertheless,aluminum alloys are prone to corrosion and require strict surface treatment before use.The conventional chromate conversion coating technology,which contains the highly carcinogenic Cr⁶⁺,has been explicitly prohibited due to its harmful effects.Therefore,the development of environmentally friendly chemical conversion technology for aluminum alloys,which is conductive and corrosion-resistant,holds great academic and practical value.Such technology not only solves the environmental pollution problem caused by hexavalent chromium at its source,but also improves the corrosion resistance of aluminum alloys as electromagnetic shielding materials.This improvement helps prevent electrostatic accumulation and enhances their electromagnetic interference and other properties.Against this backdrop,a low-contact,corrosion-resistant,and environmentally friendly conversion process was developed for 6063 aluminum alloy.Two conversion coatings,the Mo/Ti/Mn/Ga conversion coating and the Mo/Ti/Sn conversion coating,were prepared by adding different film-forming additives to the molybdenum-titanium-based solution.The focus was on analyzing the effect of sodium stannate on the film layer and examining the molybdenum-titanium-tin conversion coatings.The discussion revolved around the influence of sodium stannate on the coatings,the coating formation mechanism,and the corrosion resistance mechanism of the Mo/Ti/Sn conversion coatings.The main research contents and conclusions are summarized as follows:（1）Orthogonal and single-factor experiments were conducted to investigate the optimal process for preparing two transition metal conversion coatings.The process parameters included（NH₄）₂MoO₄ 6 g/L,H₂TiF₆ 2 g/L,Na₂SnO₃ 2 g/L,6 min,pH=4.8.Spotting time and surface contact resistance were used as evaluation indexes.The Mo/Ti/Mn/Ga conversion coatings exhibit weak adhesion,which can result in cracking and peeling,and the conversion solution is susceptible to precipitation and aging.On the other hand,the addition of stannate in the conversion coating reduces the likelihood of microcracks and enhances the density of the coatings.Additionally,the Mo/Ti/Sn conversion process requires lower energy consumption,and the conversion solution can be reused multiple times,yielding favorable conversion effects.These features highlight the environmentally friendly and sustainable advantages of the Mo/Ti/Sn conversion process.（3）Compared to the Mo/Ti/Mn/Ga conversion coatings and the substrate,the analysis of the corrosion resistance experimental results of the Mo/Ti/Sn conversion coatings revealed that the optimal Mo/Ti/Sn conversion coatings sample exhibited a spot dripping resistance of 238s,which was significantly higher than that of the substrate.The corrosion current density was also observed to be twice as low as that of the substrate,and the coatings resistance（R_c）was approximately 50 times higher than that of the substrate.（4）After conducting the conductivity analysis of the conversion coatings,it was observed that the surface contact resistance（ECR）of the Mo/Ti/Sn conversion coatings was significantly lower,measuring at 0.1343Ω/in²,accompanied by a minimal surface roughness of 94.4 nm.Furthermore,the composition analysis revealed that the Mo/Ti/Sn conversion coatings were predominantly composed of MoO₃,MoO₂,SnO₂,and Al₂O₃.This suggests that more conductive oxides are present on the surface of the conversion coatings,resulting in a larger actual electrical contact area and improved electrical conductivity.（5）The analysis of Mott-Schottky curves and UV forbidden band width has revealed that the Mo/Ti/Sn conversion coatings exhibits properties of a p-type semiconductor,with a high carrier concentration of 9.274×10²⁰ cm^-3 and a narrow forbidden band width of 2.232 eV.This indicates that the addition of Sn⁺significantly increases the carrier concentration of the semiconductor coating,resulting in a narrower band gap,and thus effectively enhances the electrical conductivity of the coatings.