Aluminum alloys environment-sensitive cracking

Relationship of Composition and Heat Treatment to Environment-Sensitive Cracking of Aluminum Alloys. Those aluminum alloys strengthened by cold working only, particularly the 1000-series alloys, do not develop susceptibility to SCC. The so-called high-strength alloys are strengthened by thermal/mechanical treatments, which result in solid-state precipitation of one or more intermetallic phases that restrict dislocation motion and, hence, increase strength. Their susceptibility to SCC varies extensively with alloy composition and the thermal/mechanical treatment. While susceptibility tends to increase with... 

Some films are termed "passive," for stainless steels or aluminum alloys, for instance. These films can play an important role in environment-sensitive crack initiation and fracture. Under thermodynamic equilibrium conditions, the film stability may be inferred from E =/(pH) diagrams, where E is the electrical potential related to the chemical free energy G by G = -nEF, and F is Faraday s number. At equilibrium, one can define the electrode potential (related to AG) and the current density I (I e here AG is the activation energy of dissolution). 

Aluminum alloys, particularly the high-strength compositions, are susceptible to environmental cracking, both in aqueous environments and in air as a function of relative humidity. This susceptibility is particularly sensitive to alloy composition and thermal treatment, which is shown by differences in the dependence of ductility on strain rate. Understanding these differences can contribute to identification of mechanisms of the strain-rate sensitivity. A summary of the influence of strain rate on the ductility of 2000-, 5000-, and 7000-series aluminum alloys in environments represented by 3% NaCl + 0.3% H202 is shown in Fig. 7.84 (Ref 121). The 7000 series shows susceptibility to hydrogen embrittlement at strain rates below 10 5 to 10-6 s 1. Although there is... 

Gangloff, R. P., Environment Sensitive Fatigue Crack Tip Processes and Propagation in Aerospace Aluminum Alloys, in Fatigue 02, Anders Blom, Ed., Engineering Materials Advisory Services, West Midlands, UK, 2002, pp. 3401-3433. 

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