Aluminum-copper alloys, intergranular

Corrosion activity may develop because of some heterogeneity in the grain boundary structure. In aluminum-copper alloys, precipitation of AI2CU particles at the grain boundaries leaves the adjacent solid solution anodic and more prone to corrosion. With aluminum-magnesium alloys, the opposite situation occurs, since the precipitated phase Mg Als is less noble than the solid solution. Serious intergranular attack in these two alloys may however be avoided, provided that correct manufacturing and heat treatment conditions are observed. 

An experimental magnesium-base alloy sheet containing 14 % lithium and 2 % aluminum was reported to have experienced intergranular layer attack similar to the exfoliation of 2duminum-copper alloys [8],... 

Intergranular cracking may be caused by liquid metal embrittlement if the alloy is under tensile stress, either residual or applied. While mercury embrittles copper, the severity increases when alloyed with aluminum or zinc. This embrittlement occurs in both tension and fatigue and varies with grain size and strain rate. Other aUo5ing elements such as lithium, sodium, bismuth, gallium, and indium also affect embrittlement. 

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. 

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... 

Embrittlement under creep conditions of, for example, aluminum alloys and steels that results in abnormally low rupture ductility. In aluminum alloys, iron in amounts above the solubility limit is known to cause such embrittlement in steels, the phenomenon is related to the amount of impurities (for example, phosphorus, sulfur, copper, arsenic, antimony, and tin) present. In either case, failure occurs by intergranular cracking of the embrittled material. 

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