Study On Pretreatment And New Chemical Conversion Technology Of 6063 Aluminum Alloy

Due to small density,high specific strength,good plasticity and formability,good thermal conductivity,etc.,Aluminum and its alloys were favored by the transportation,building materials,aerospace and electronics industries.It's easily for Aluminum to generate a layer dense film by oxidized in the natural environment.However,in the special environment such as oceans,acids,and alkalis,the protection performance of the layer is extremely limited and can't meet the application requirements.Therefore,it is of great significance to study the corrosion protection technology of aluminum and its alloys,to ensure the safety of aluminum alloy products and expand its applicationIn this paper,6063 aluminum alloy was used as the research object,takes the development of new chemical conversion technology in an environment-friendly method as the research goal.the aluminum alloy surface pretreatment and new environmental protection chemical conversion technology were studied.The main research work and achievements of the paper are as follows:1)Study on pretreatment process:Employing the newly developed H₃PO₄-Na₂MoO₄based chemical conversion bath,the effects of nine typical pretreatments procedures on the surface modification of 6063 Al alloy extrusion profile were investigated.select the best pretreatment process plan,and The membrane effect influences significant process steps to optimize the process.The final selection of the pretreatment process used in this study was as follows:alkali erosion?40g/L NaOH,20 g/L NaCO₃,20g/L Na₃PO₄,50?,2 min??speckles filtering?35%HNO₃,100g/L Fe?NO₃?₃,3g/L additive A,RT,7 min??alkali activation?10g/L NaOH,RT,30 s?.The SEM and EDS analysis results of the surface of a typical pretreated sample show that the despeckling process has the function of adjusting the microstructure of the aluminum-based surface and reconstructing the surface microstructure;additional alkali activation can impart surface activity,and the second phase of the substrate surface is slightly exposed.Film formation efficiency increases.2)Study on new chromium-free chemical conversion process:Based on the pre-optimized pretreatment process and the mian technical indicators of surface density,corrosion resistance,binding force and macro morphology.and the active ingredients of the conversion liquid are selected and studied for conversion.The formula of the liquid formulation and conversion parameters affecting the film forming effect finally locks the H₃PO₄-Na₂MoO₄ based chemical conversion solution as follows:20ml/L H₃PO₄,4g/L ZnO,1.5g/L Na₂MoO₄?2H₂O,2g/L Complexing agent B,1g/L promoter C,water-based compound solution,pH=2.0,T=45°C,t=10 min.The results of SEM and EDS analysis of a typical conversion film sample show that the conversion film is mainly composed of O,P,Zn and Mo elements,and the film structure is uniform and dense,with discrete micro-cracks distributed between the lips.3)Study on the effect rules of low surface energy modification:Based on the optimization of the pretreatment,conversion solution formulation and conversion parameter system,the effect of surface modification on the conversion film properties was studied,and the final modification process was determined as follows:15 g/L stearic acid ethanol-based solution,Immersion method,processing temperature 80°C,processing time 1h.After the surface modification treatment,the drip time of the conversion film can reach as long as 216s,which is2.5 times before the modification.SEM observations show that the stearic acid modification treatment has a significant sealing effect on the micro-cracks,pores,cracks and other micro-defects in the chemical conversion film layer;stearic acid self-assembles on the surface of the conversion film,and a conversion film is prepared on the aluminum-based surface.For the skeleton,the stearic acid hydrophobic layer is a closed layer composite film.