The Corrosion Resistance Research Of Fluoroaluminate-phytic Acid On The Surface Of 5052 Aluminum Alloy

Due to its excellent properties,aluminum alloy materials are widely used in aviation,military,medical and other fields.In order to prolong its service life,chromate conversion is usually used to enhance its corrosion resistance ability.However,hexavalent chromium in chromate not only do harm to the human health but also cause environmental pollution.Many principles have been introduced to limit its widely use around the world.Therefore,A novel chromium free conversion film with high corrosion resistance ability and environmental friendly is urgently required for application.Based on the successful preparation of the fluoroaluminate conversion film by the research team in the early stage,the fluoric acid was screened out by single-factor experimental method to seal the fluoroaluminate conversion film on the surface of 5052 aluminum alloy.The optimal composition and conditions of the conversion solution were obtained by optimizing the composition and conditions of the conversion solution: sodium fluoride 5g / L,titanium oxysulfate 0.5g / L,p H 4.5,reaction temperature 40°C,and reaction time 20 min.Phytic acid 30 ml / L,p H 4.5,blocking temperature 55 ° C,blocking time 5min.The experimental results show that the resistance to neutral salt spray time of the conversion film can reach 96 h.Scanning electron microscopy and EDS spectroscopy analysis results show that after the blocking treatment,the conversion film is composed of closely packed crystal particles and has a good binding force with the metal matrix.The mass fraction of each element in the fluoroaluminate conversion film after phytic acid blocking is: F31.35%,Al46.17%,Na18.73%,the main film-forming elements after sealing become F30.01%,Al46.49%,Na15.01%,C3.04%,P0.22%,phytic acid The self-corrosion current density of the fluoroaluminate conversion film after sealing decreased from 4.3 × 10-6A·cm-2 before sealing to 2.3 × 10-6A · cm-2 after sealing.The optimal condition for the conversion film after sealing was corrosion.The current density was reduced by about 47%(equivalent to slow release efficiency).After the best conditions,the substrate has a neutral salt spray resistance time of 96 hours,which has reached the standard for industrial applications.