Published: Jan 1957
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It was natural that among the early activities of ASTM Committee A-5 on Corrosion of Iron and Steel and Committee B-3 on Corrosion of Non-ferrous Metals and Alloys, consideration should be given to the use of protective metallic coatings. When Committee A-5 was organized in 1907, the principal metallic coating used on steel was zinc, then generally applied by hot-dipping. In 1922 when Committee B-3 was organized, the metallic coatings on non-ferrous metals were usually applied by electroplating, but for appearance rather than for protection. The first recorded specific studies by ASTM on electroplated coatings were started about 1927 by A-5 Subcommittee on Hardware Specifications (now Subcommittee XIII). In this investigation, steel articles of many shapes, including those used in pole-line hardware (plates, angles, washers, bolts, and nuts) were coated by various methods, including hot-dipped, sherardized and electroplated zinc; electroplated cadmium; hot-dipped lead; and hot-dipped aluminum. Specimens of each kind were exposed in several locations, including New York, N. Y., Sandy Hook, N. Y., Pittsburgh, Pa., State College, Pa., and Key West, Fla.; and were inspected at intervals by interested members of the subcommittee. The results that were reported within a few years were unfavorable to the electroplated zinc and cadmium coatings. In the light of present knowledge, this observed inferiority of electroplated coatings was at least partly caused by the following: 1. The specimens were all prepared under commercial conditions, with no special efforts to produce uniform coatings. In other words, they were typical of what was then being done, rather than of what might be done. 2. By the methods then used commercially, the electroplated coatings were much thinner than the hot-dipped coatings. (This is a valid argument for the use of electroplating when only thin coatings are required.) 3. Many of the shapes, especially the angle irons, were such that electroplating did not furnish as nearly uniform coatings as were normally produced by hot-dipping. Hence the plated coatings usually failed at those points where the coatings were abnormally thin. 4. No systematic effort was then made to measure the average or minimum thickness of the coatings produced by the various methods. This apparent oversight was caused in part by the lack, at that time, of convenient reliable methods for measuring the minimum thickness of coatings.
Consultant, Washington, D. C.