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In 1958, exposure tests were started in rural, marine, and urban atmospheres in Sweden, covering 36 copper alloys in sheet or rod form. Test results after two and seven years' exposure have been reported earlier. this is the concluding report of the tests as completed after 16 years' exposure.
Greenish coatings had developed on most of the materials after six to seven years at the urban and marine sites. At the rural site, however, no distinct green coating had developed on any material after 16 years, only different shades of black or brown. The amount of patina retained increased substantially from 7 to 16 years of exposure. The patina was found to be more protective in the marine and rural atmospheres than in the urban one. The patina was also examined by X-ray analysis and scanning electron microscopy-EDX.
The average penetration (determined gravimetrically) during 16 years of exposure had stabilized at the following levels:
0.3 to 0.5 µm/year in rural atmosphere
0.5 to 0.9 µm/year in marine atmosphere
0.9 to 1.3 µm/year in urban atmosphere
The dezincification rate of brass had decreased somewhat during the period from 7 to 16 years. It was highest for brasses with an (α + β)-phase structure, the maximum dezincification depth measured metallographically after 16 years being 90 to 215 µm, the loss in ultimate tensile strength 5 to 15 percent and the reduction in elongation up to 30 percent.
copper, copper alloys, atmospheric corrosion tests, field tests, patina coatings, dezincification
Corrosion metallurgist, Gränges Metallverken, Research and Development, Västerås,
Director, Swedish Corrosion Institute, Stockholm,