Intergranular corrosion copper alloys

Test methods for determining electrolytic corrosion with electrical insulating materials Method for determination of resistance to intergranular corrosion of austenitic stainless steels copper sulphate-sulphuric acid method (Moneypenny Strauss test) Specification for electroplated coatings of tin/lead alloys... 

Intergranular corrosion occurs in stainless steels and alloys based on nickel, aluminium, magnesium, copper and cast zinc. In the following sections we shall look at the three former groups in some detail. 

Several aluminium alloys show very good corrosion resistance in various atmospheres. Some pitting occurs, but the pits remain small. Maximum depth seldom exceeds 0.5 mm during 6-20 years of exposure it is usually in the order of 0.1 mm. Some alloys may, however, be attacked by intergranular corrosion or exfoliation corrosion (see Section 7.7). Extensive galvanic corrosion may occur on aluminium in contact with copper, mild steel (in marine atmosphere) and graphite, less in contact with stainless steel, while aluminium is compatible with zinc [8.2]. 

Copper-base alloy, brass, bronze Surface and intergranular corrosion Blue or blue-green powder deposit... 

The general and intergranular corrosion of most of the alloys tested was reduced by copper additions, with the exception of alloys 13 and 17, which had very high combined tin and lead contents. Outdoor, 2 year exposures showed very similar results. In conclusion, Kehrer suggested reducing the allowable tin content of die castings to 10 ppm and the combined lead and cadmium level to 60 ppm. 

Dynamic, as well as static, tests with a ZA-8 pump prototype gave a top ASTM D-2809 rating even though inadequate inhibitor was present and, consequently, copper (from the tubing) deposited onto the alloy surface. Intergranular corrosion was minimal, with pits no more than 100 (xm deep after a 300-hour test (Noranda, 1992). 

Determination of resistance to intergranular corrosion of stainless steels—Part 2 Ferritic, austenitic and ferritic-austenitic (duplex) stainless steels—Corrosion test in media containing sulfuric acid Corrosion of metals and alloys— Determination of dezincification resistance of brass Copper alloys— Ammonia test for stress corrosion resistance Corrosion tests in artificial atmosphere—General requirements... 

For instance, when Al-Cu alloys are heat-treated by delayed quenching after solid-solution treatment, copper will diffuse to the grain boundaries. The copper-poor regions formed adjacent the grain boundaries play an anodic role relative to the other regions which have more noble potentials (Galvele and Micheli, 1970). Some aluminum alloys subjected to inadequate quench treatment become susceptible to intergranular corrosion. 

Schematic of grain boundary region in a 2XXX alloy. Precipitation of the very-high-copper-content precipitates on the boundary causes a copper-depleted zone on either side of the boundary. The difference in the electrochemical potentials of the copper-depleted zone and the copper-rich matrix form a strong galvanic cell with a potential difference of about 0.12 V. Furthermore, the anodic copper-depleted zone is small in area compared with the area of the cathodic grain matrix, resulting in a high driving force for rapid intergranular corrosion. (Courtesy of Alcoa Technical Center, Edward L. Colvin.)...

All metals and alloys are joined together by grain boundaries. The intergranular corrosion of steels, brasses, bronzes and aluminum alloys containing copper is of particular interest to engineers. Because of the importance of steels, the largest amount of work reported in the literature is on steels. It would be, therefore, appropriate also here to review the phenomenon of intergranular corrosion with a particular emphasis on steels. It would be appropriate, hence, to review... 

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