| With the expansion of the application range of aluminum alloy products and the deterioration of service environment,higher requirements are put forward for the performance of aluminum alloy.General ly,the failure of aluminum alloy occurs on the surface of parts,so surface treatment of aluminum alloy parts is an effective way to improve the performance of aluminum alloy.Among the different surface modification technologies,the chemical conversion coating of chromium ion has attracted much attention due to its excellent corrosion resistance.At present,the corrosion resistance of most chromium ion chemical conversion coatings is rated according to GB / T 6461-2002,which is below grade 8.However,it can not meet the requirements in the service environment with high requirements for corrosion resistance.Therefore,it is an urgent task to improve the corrosion resistance of Cr ion chemical conversion coating.In this paper,chromic acid chemical con version coating was prepared on aluminum alloy surface by chemical im pregnation process optimization.The surface morphology,chemical composition and thickness of the conversion film were studied by SEM,EDS and AES,the effects of chemical conversion sol ution composition and film thickness on the film quality were analyzed.According to GJB150.11-1986,salt spray test and corrosion resistance evaluation of the conversion coating were carried out,and the formulation of hexavalent and trivalent chromium ch emical conversion treatment solution with good corrosion resistance was obtained.There are two reasons for the improvement of corrosion resistance of Cr ion chemical conversion coating: first,a more uniform and compact chemical conversion film is obtained,which hinders the contact between corrosive medium and substrate,reduces the corrosion rate;two,it improves the adhesion of the surface film layer,and makes the surface film layer is not easy to peel off the substrate.The results show that the prepared chemical conversion coating is uniform and compact,with few micro cracks.The Cr(VI)conversion coating with a thickness of 480-540 nm has good uniformity,corrosion resistance and adhesion to the substrate.According to GB / T 6461-2002,the corrosion resistance of chemical conversion coating is above grade 8.The corrosion resistance of chemical conversion coating prepared by trivalent chromium chemical conversion treatment solution can reach grade 9. |
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