AlCu alloy

Figure 34.24. Crack in the mushy or semisolid zone of a stressed AlCu alloy. The elliptically marked area denotes a region in which filling by the melt is impeded by a solid bridge. Observation was made through a silica aerogel.

AlCu alloys containing a very reactive element and a seminoble metal of extremely different electrochemical properties, anodic oxidation causes the preferential oxidation of Al, which forms passivating aluminum oxide films whereas Cu remains at the metal surface. Although... 

Among aluminium alloys, particularly those with high strength within the AlZnMg and AlCu series have been liable to SCC. In heavily cold-worked AlMg alloys with Mg content > 5% and in cast AlCuSi alloys, SCC may also occur. Finally, it may be developed in AIMgSi alloys after poor heat treatment [7.27]. 

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