Comprehensive Study Of Corrosion Resistance Of Al Alloy 6101 In Alkaline Solution By Means Of Coatings

The improvements of corrosion resistance of Al alloy 6101 in alkaline solution by means of coatings（organosilane-epoxy,chromium-free deposition of cerium-based conversion coating）are studied.The evaluations include electrochemical test potentiodynamic polarization（PDP）,electrochemical impedance spectroscopy（EIS）,effective weight loss of corrosion in the alkaline solution of sodium hydroxide（Na OH）having p H 11,water contact angle,peeling off test,scanning electron microscope（SEM）,energy dispersive x-ray spectroscopy（EDS）,surface adhesion and scratch tests,etc.Following achievements are obtained:（1）As to the organosilane-epoxy coating,the optimal ratio of coating to toluene of the dipping solution is 1:4.5.The peeling off strength of this coating on Al alloy is 0.144 F/N,the critical load to scratch damage the coating surface is 20.982g,the water contact angle becomes 106°,and the results potentiodynamic polarization（PDP）measurements,electrochemical impedance spectroscopy（EIS）and effective weight loss tests of coated Al immersed in alkaline solution of Na OH with p H 11 show that the protection efficiency of this coating in the base solution reaches to about 99%at the optimal ratio of OE to toluene.（2）Optimize pigment volume concentration of zinc phosphate pigments can protect Al alloy6101 from alkaline media.Additionally,zinc phosphate pigments form a shielding film on the substrate and facilitate stopping the penetration of the aggressive corrosion ion.The efficiency of eco-friendly zinc phosphate pigments is almost 98%during the analysis.Comparative study of physical aging of organic–silicone epoxy and Zinc Phosphate（ZP）pigment modified organic–silicone epoxy coatings on Al alloy 6101 is conduct in Xi’an China for one year in all four seasons where in summer for 3 months results degraded more due to high UV radiation and humidity,it is found that totally peeling force of ZP pigments modified epoxy coatings is 50%higher of than that of the neat epoxy coatings though both peel-off adhesion strength and scratch test visibility decreased in both coatings;The electric resistance of ZP pigments modified epoxy coatings is about 30%higher of than that of neat epoxy coatings,the corrosion rate of ZP pigments modified epoxy coatings is about 70%lower of than that of neat epoxy coatings;Optical surface observation of the coatings showed that the ZP modified organic–silicone epoxy coating could effectively restrict the crack and shrinkage in coatings after aging exposing in natural environment.（3）As to the chromium-free deposition of cerium-based conversion coating,a chromium-free,eco-friendly chemical conversion coating for aluminum alloy 6101 used in the chemical industry for different purposes is evaluated.Immersion in two cerium salt sources（chloride-and nitrate-based）assisted with hydrogen peroxide（H₂O₂）resulted in the deposition of cerium-based conversion coatings on aluminum alloy 6101.With a p H 11 alkaline solution of Sodium hydroxide（Na OH）,electrochemical measurements were performed to assess corrosion behavior,including mass loss measurements（14 days）,free corrosion potential,polarisation,and electrochemical impedance spectroscopy.The results show that there are improvements of 96%in corrosion resistance,in the presence of selectively deposited cerium-based conversion coating.（4）Graphene oxide（GO）concentrated slurry dispersion method was used to prepare the GO epoxy thermal insulation and anti-corrosion coating on carbon steel.Corrosion test was carried out in 3.5%Na Cl solution at 50°C,and a thermal testing device tested thermal insulation performance.The results of the electrochemical corrosion test after 456 h show that the low-frequency impedance of the coating with 0.5%GO-modified significantly improved,and the corrosion resistance of the coating is better than that of the coating without GO and 1.0%GO-modification.SEM analysis results show that surface morphology of the coating modified with GO 0.5%and 1.0%after 456 h of corrosion,there were no cracks and corrosion products at the substrate interface.In contrast,coatings without GO modification has apparent corrosion damage.Before corrosion testing,the thermal insulation performance of coating modified by 0.5%,1.0%GO coating was not significantly different from that of the neat epoxy.The bonding strength is also reduced to 3.9,2.3,1.0 MPa.The experimental results show that the coating with 0.5%GO modified is the best for corrosion resistance and insulation.