Performance of Aluminum Alloys at Other Test Sites

Abstract

The well documented pattern of corrosion behavior for aluminum alloys is confirmed for the seven-year exposures at Corpus Christi, Tex.; Richmond, Va.; McCook, Ill.; and the Kure Beach, N. C., 800-ft site. A decrease in the corrosion rate, as determined by weight loss, was evident for all sheet alloys after about the second exposure year. Likewise, the depth of pitting decreased with time: very slight increases in depth were noted between the second and seventh years in most cases. Results indicate that the McCook site is the most severe, with the Richmond location, the Corpus Christi exposure, and Kure Beach 800-ft site in order of decreasing severity. The value of cladding basic alloys such as 3003 and 6061 was demonstrated again. The claddings effectively protected the core alloys from pitting and general corrosion and the clad alloys showed negligible changes in mechanical properties at all sites after seven years. Other than the 2024 aluminum-copper alloy which showed intergranular corrosion for some hard tempers at the most severe sites, all alloys showed pitting corrosion to some extent. Maximum pit depths included 14.7 mils for the 2024-T36 alloy, 10.0 mils for the 5154-H34 aluminum-magnesium alloy, 5.2 mils for the aluminum-magnesium silicide alloy 6061-T6, and 6.3 mils for the high-purity aluminum sheet. With the exception of the 2024 metal, these deepest pits occurred at the McCook site. The deepest pit found on the Kure Beach 800-ft site panels measured 6.1 mils, and the deepest pit for most Corpus Christi panels was 5.4 mils (2024 alloy panels having some intergranular attack had measured pits as deep as 14.7 mils). A corrosion rate of 0.175 milligrams per square decimeter per day (mdd) for 2024-T36 alloy at McCook was the highest found. If we exclude the 2024 alloys, no corrosion rate greater than the 6061-T6 rate of 0.125 mdd was found. High purity aluminum showed rates from a low of 0.004 mdd at Kure Beach to 0.044 mdd at McCook.

Bi-modal trend in the long-term corrosion of aluminium alloys

“…There are only a few data sets for long-term exposures. These include the 20 year data for a variety of environments in the USA [5], the 16 year study of aluminium pitting and mass loss in marine environments in the Panama Canal Zone [6], the 7 year data for in-land atmospheric corrosion, also in the USA [7], the 10 year observations for various atmospheric exposure conditions in Sweden [8] and the 30 year observations of atmospheric corrosion in mainland USA [9]. The data from these laboratory studies and empirical field studies mostly have interpreted the data in terms of the well-known and widely applied power-law function for the corrosion of metals as a function of time:…”

Reliability Assessment of Aircraft Structure Joints under Corrosion- Fatigue Damage

“…Several long-term studies have been done to determine the statistical effects of environmental exposure on 2024-T3 aluminum materials [53,54]. The first study [53] was conducted under the direction of the Atmospheric Exposure Test Subcommittee of ASTM Committee B-7 on Light Metals and Alloys.…”

“…The second test program [54] involved four test sites for periods of 1, 2, and 7 years. The four tests sites represented rural marine (Kure Beach), industrial marine (Corpus Christi, TX), moderate industrial (Richmond, VA), and industrial (McCook, IL).…”

“…These models are the Wei corrosion-fatigue (WCF) model [53,54], the crack-closure corrosion-fatigue (CCCF) model [42], and the simultaneous corrosionfatigue (SCF) model [8]. Then, three corrosion-fatigue damage models are presented.…”

Time Dependent Development of Aluminium Pitting Corrosion

“…However, it also has been applied to data from a number of long-term exposure studies (up to 20 years) and for these deviations from (1) have been noted. Usually these deviations have been dismissed as the result of experimental or recording error (see Ailor [7] for a summary). Much of the information about corrosion of aluminium and its alloys is presented in terms of mass loss and most of it is for atmospheric corrosion.…”