Metal Finishing Guide Book


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Page 329 of 843

Table IX: Comparison of Zinc Alloy Plating Processes Plating Bath Zn Sn-Zn Zn-Ni Zn-Ni Zn-Co Zn-Fe Appearance Alkaline B Neutral C Alkaline B Acid B Acid B Alkaline B Solderability C A D D D D Wear-resistance C D A A C C Whisker D B B B D D Crimping, bending B A B D C C White C C A A C C Red C A A A C C Corrosion After White D C A B D D resistance baking Red C C A C D D After White C C A C D D Red C A A C D D A C A D A A C General crimping Throwing power Plating rate C B C A C Covering power B A B B B B Bath control A B B D C C Blue Clear Clear Clear Clear Yellow Black Black Chromate availability Yellow Replatability Black A C C C B B Anodes Zinc/ Tin/zinc Nickel Zinc/ Zinc Zinc Auxiliary anode steel A alloy C plated A nickel D A A B B C C B B X-ray A B B B B B Kocour A B B C B B X-ray - B B C D D Waste water Thickness Composition Relative price Analysis Black - B B B C D 1.0 2.5–3.0 2.5–3.0 1.5 1.2 1.1 A: Excellent B: Good C: Fair D: Poor the alloy has good welding characteristics and workability, and can readily be used on electroplated strip steel. It is also suitable as a base for paint. Of the alloys being considered, zinc-iron will generally give the least improvement in corrosion resistance compared with conventional zinc. If the iron content of the bath gets too high, blistering problems, including delayed blistering, may occur. Corrosion resistance of chromated zinc-iron plated parts drops drastically after exposure to temperatures over 250°F (see Tables V and VI for acid and alkaline bath parameters). 322

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