Zirconium-based conversion coating (ZrCC) was successfully prepared on the samples of coldrolled steel from the solution of H 2 ZrF 6 and HNO 3 at controlled pH. Its surface morphology was analysed by the 3D optical microscope and scanning electron microscope. Its chemical composition and structure were investigated by energy-dispersive X-ray spectroscopy, X-ray diffraction analysis and X-ray photoelectron spectroscopy. The open-circuit potential measurement was used to study the coating formation process, and the electrochemical impedance spectroscopy test was employed to analyze the behaviors of the coatings prepared at different deposition time. According to the analysis results, the deposition mechanism of ZrCC on steel was proposed, and the chemical schematic diagram was also designed. The corrosion resistance performance of ZrCC with cathodic electrodeposition primers was also evaluated by salt spray exposure of 1000 h.

Tin compound additions to polyvinyl butyral type clear primers provided very effective corrosion inhibition when applied to magnesiumsteel galvanic couples.A combination of tributyltin oxide and finely divided metallic tin dust added to the clear primer offered the best protection by increasing the corrosion resistance 90% over noninhibited primers.A major program evaluating the most promising finishing systems developed during this and previous contracts was initiated and involved 20% salt spray, rural and marine exterior exposures. Salt spray tests again showed the advantages of tin electroplated fasteners over cadmium plate when used in conjunction with Dow #17 Anodizing and various paint systems. The stannate coating gave results superior to Dow #17 and cadmium or phosphate coated steel fastener systems.After prolonged periods of exposure at minus 400, electroplated tin on steel showed a slight transformation from Beta "white tin" to Alpha "gray tin", however, salt spray tests indicated no detrimental effects in corrosion resistance. Known methods of eliminating this phenomenon include additions of impurities such as 0.1% bismuth to the metal.Weatherometer tests of LA124 alloy magnesium panels that were part of the finishing studies for the M113 hull were completed. After 650 hours exposure, the corrosion characteristics of painted and unpainted panels, with and without steel fasteners comparing Dow #17 anodizing and the stannate coating were very encouraging. Similar panels exposed to rural exterior atmospheres for 15 months showed the same good results with very little or no galvanic corrosion. Good paint adhesion characteristics of the stannate coating were also shown.Electrical resistivity measurements to determine the conductivity of the stannate coating showed only 8.0 microhms per square inch as compared to 7.0 microhms for bare magnesium and a high of 74,000 microhms for Dow #17 thin anodize.-2-The development, improvement and finalization of the stannate process involved considerable effort during this contract period. Several factors relating to known or expected problems such as chromate poisoning of the bath, powdery coatings, failure of steel components to coat, and pretreatment methods were explored.Steady improvements of the stannate application process were achieved and tentative processing bulletins were revised to include the new developments as they were proven. The most recent bulletin includes the best known procedures for applying the stannate coating. The operational limits of the bath, methods of analysis, a few operational difficulties that may arise, and sources of supply of chemicals.The stannate process was finalized for patent coverage and the case was filed on August 8, 1961. Patent coverage for the addition of tin dust to clear primers has also been in process for some time and should be ready for filing in the near future.

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