Corrosion Resistance Of 8-Hydroxyquinoline Modification For Fluoroaluminate Conversion Coating On 3003 Al Alloy

Al alloy has been very widely used in many fields due to its excellent mechanical properties,smaller relative density,better impact resistance and other characteristics.However,because of its reactive character and corrosivity,it is necessary to conduct an anti-corrosion treatment on Al surface.Although chromate conversion coating technology is the most frequently used method of the treatment of Al and Al alloys surface,chromate seriously pollutes the environment and has been explicitly banned to use internationally.Therefore,the research and application of green chromium-free conversion coatingtechnology on Al alloy have great practical significance.Aiming at the unsatisfactory result of the corrosion resistance of fluoroaluminate conversion coating on Al alloy prepared by our research group,this paper focused on the modification of corrosion resistance of phytic acid,tannic acid and 8-hydroxyquinoline on fluoroaluminate conversion coating on 3003 Al alloy.The single factor experimental results showed that the corrosion resistances of three organic compounds on fluoroaluminate conversion coating on Al alloy were enhanced.Among them the modification effect of 8-hydroxyquinoline was the best,the neutral salt spray time reached to 210h;tannic acid was second,160 h and phytic acid 96 h.It was discovered thatthe composition of the conversion solution and the optimal film formation conditionsmodified by 8-hydroxyquinoline of fluoroaluminate conversion coating on 3003 Al alloy were as follows: sodium fluoride 3.5g/L,8-hydroxyquinoline 0.9g/L,pH 4.0,titanyl sulfate 0.5g/L,reaction temperature 45?and reaction time 10 min.The neutral salt spray timeof the coating was improved from 36 h before modification to 210 h after modification,much more than 96 h of industrial application standard.The analysis results of scanning electron microscopy(SEM)and energy dispersive spectrometer(EDS)showed that fluoroaluminate conversion coating on 3003 Al alloy modified by 8-hydroxyquinoline was composed of C 0.93%,O 0.61%,F 59.37%,Na 22.30% Al 14.10%,Ti 0.10%,Cu 2.60%,Mg 0.07%(mass fraction).The coating was still composed of crystal sodium fluoroaluminate,but the coating surface was covered by the dense,good adhesive and amorphous structural organic film formed by the reaction between aluminum and 8-hydroxyquinoline,which made the corrosion potential of Alalloy move 44 mV positively and the corrosion current decrease by about 11%.Therefore,the corrosion resistance of Alalloy was greatly improved.