INVESTIGATION OF THE DEGREASING PROCESS TO IMPROVE ADHESION BETWEEN OXIDIZED GALVANNEALED COATING AND ELECTROPLATED NICKEL
In this present work, it was investigated that zinc oxide layer (i.e. corroded zinc) was formed on top of older GA surface cannot be removed or dissolved by conventional alkaline solution. This has resulted in poor adhesion between GA and secondary electroplated coating. Those secondary coating peeled off during high temperature process and 900 bend test. In this work, modifications were done during degreasing process which improve the adhesion of secondary electroplated coating. High concentration degreasing solution (pH 12.5) was used and the dipping time of the sample into the degreasing solution was increased from 20-30 sec to 40-90 sec. This enhances the dissolution of the zinc oxide layer from top of the GA coating and improves the adhesion between GA and electroplating coating. Ni anode, conventional Watt’s bath and current density 400 A/m2 for 5 & 8 minutes were maintained for electroplating. Ni coating thickness was maintained 3-6 µ. Coating thickness, cross-section, compositional analysis was done by using scanning electron microscopy (SEM), adhesion was checked by high temp 900 bend test, Additionally the wettability property also improved (turns hydrophobic from hydrophilic) due to Ni electroplating which was confirmed by contact angle instrument.
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