Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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Page 267 of 707

Table IX: Comparison of Zinc Alloy Plating Processes Plating Bath Zn Appearance Solderability Wear-resistance Whisker Crimping, bending General Corrosion resistance After baking After crimping Throwing power Plating rate Covering power Bath control Chromate availability Replatability Anodes Auxiliary anode Waste water Thickness Composition Relative price X-ray Kocour X-ray Analysis White Red White Red White Red Alkaline B C C D B C C D C C C A C B A Blue Yellow Black A Zinc/ steel A B A A - - 1.0 A: Excellent C Tin/zinc alloy C B B B B B 2.5–3.0 B: Good Sn-Zn Neutral C A D B A C A C C C A C B A B Clear Zn-Ni Alkaline B D A B B A A A A A A A C B B Clear Black C Nickel plated A C B B B B 2.5–3.0 Zn-Ni Acid B D A B D A A B C C C D A B D Clear Black C Zinc/ nickel D C B C C B 1.5 C: Fair D: Poor electroplated strip steel. It is also suitable as a base for paint. Of the alloys being con- sidered, zinc-iron will generally give the least improvement in corrosion resis- tance 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). TIN-ZINC 266 A number of electrolytes are available for deposition of tin-zinc alloys. These Zn-Co Acid B D C D C C C D D D D A C B C Clear B Zinc A B B B D C 1.2 Zn-Fe Alkaline B D C D C C C D D D D A C B C Yellow Black B Zinc A B B B D D 1.1

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