Study On Sherardizing-low Chromium Dacromet Composite Protection Technology

Powder sherardizing has high bonding strength, good wear resistance. Dacromet coating has salt corrosion. However, the low chromium of dacromet coating has become a research hotspot.The composite protection technology which combined powder sherimdizing with low-chrome dacromet coating is worthy of investigation. In this paper, Q235 steed was processed by powder sherardizing. And then Low-chrome dacromet coating was prepared on surface of the zinc coating.The effects of chrome substitutes on macroscopic morphology, bonding strength, corrosion resistance of the composite protective coating were studied. This article discussed the effects of chrome substitutes on th,e viscosity of dacromet solution and the coating amount.The microstructures of the cross section and the surface of the composite protective coating were analyzed. The main research results are as following:(1) When chromic anhydride is substituted respectively by ammonium molybdate, boric acid and phosphoric acid. The viscosity of dacromet solution and the coating amount reduce as the replacement amount of ammonium molybdate increases. The viscosity of dacromet solution and the coating amount have no effect as the replacement amount of boric acid increases. The viscosity of dacromet solution and the coating amount increase as the replacement amount of phosphoric acid increases. When chromic anhydride is substituted compoundly, the effeicts of substitution of chromic anhydride and proportion on the viscosity of dacromet solution and coating amount by two kinds of compound substitution or three kinds of compound substitution are positively correlated with the influences of single substitution.(2) The low-chromium dacromet coating is prepared on surface of the zinc coat. When chromic anhydride is substituted respectively or compoundly by ammonium molybdate, boric acid and phosphoric acid. The appearance grade of the composite protective coatings are all up to 1?2 level (excellent).(3) The replacement amount of chromic anhydride is 20%. The binding strength of dacromet coatings that chromic anhydride is substituted respectively or compoundly by ammonium molybdate, boric acid and phosphoric acid on the zinc coating are all bigger than or equal to the level of 3 (meet the requirements). The replacement amount of chromic anhydride is 35% or 50%.The binding strength of dacromet coatings that chromic anhydride is substituted respectively by ammonium molybdate and boric acid on the zinc coating are all bigger than or equal to the level of 3 (meet the requirements). The binding strength of dacromet coatings that chromic anhydride is substituted compoundly on the zinc coating are all bigger than or equal to the level of 3 (meet the requirements).(4) The replacement amount of chromic anhydride is 35%. The corrosion resistance of composite protective coating that is substituted by ammonium molybdate, boric acid and phosphoric acid at the ratio of 1:1:2 is the best. Resistant to ammonium nitrate rapid corrosion is up to 8.0h. The corrosion resistance of the composite protective coating is better than that of the composite protective coating with no replace. Its bonding strength can reach the level of 5.