Prevention of Micro-Flow Marks in Cathodic Electrodeposited Primer Coating in Automotive Industries

There was a defect of severe micro-flow mark lines in cathodic electrodeposited (CED) primer coating on car components. This problem was highlighted after final painting. This article describes the tests performed to determine the root cause of the defect. Tests included a surface profile of the CED coating and the determination of the microstructure and nickel content of the phosphate coating beneath the CED coating. The investigation identified the optimum concentration of nickel in the coating to refine phosphate grain size and create a unity crystal aspect ratio. It also found that the triple point junction of phosphate crystals determines the porosity to provide a uniform CED coating surface finish.

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