I Zinc - Manganese Alloy Electrodeposition Ft 343 - H , f

inc alloy electrodeposits are finding increased acceptance as improved replacements for conventional electrogalvanized finishes. Zinc-nickel appears to be experiencing the most widespread use, although zinc-cobalt and zinc-iron also have well-defined market shares. The zinc-manganese system has not been widely reported; however, some investigators have examined its corrosion resistance, polarization behavior during electrodeposition and the range of possible electrolyte^'-^ and have found it to have markedly attractive features. Some of the earliest reported work was carried out by Sagiyama et al.1,2 They were primarily interested in evaluating the performance of zincmanganese for use on automotive body panels. The bath used was based on zinc sulfate, manganese sulfate and sodium citrate. It was found that electrodeposits with a manganese content of 30-50% exhibit excellent corrosion resistance both in the prepainted and postpainted states. The work and weldabilty of the alloy were also assessed and found to be good. Selvam and Guruviah3 also reported good corrosion resistance with the zinc-manganese system. Govindarayan et al.4 carried out similar investigations using an acetic acid salt spray, and their data confirmed the superiority of alloys containing 6-75% manganese over zinc alone. One of the main drawbacks of the zinc-manganese system when electrodeposited from citrate-sulfate electrolytes is its very low cathode current efficiency. Values of 40% have been quoted, with improvements to 60% occurring with the addition of small amounts of sodium thiosulfate.2 For a viable industrial process, this is still considered low; therefore other investigators have examined alternative elect rolyte~.~ A fluoroborate bath containing both zinc and manganese fluoroboITEMPERATURE Zl0C 2042. A S 1 t .........