Accelerated Testing of Aluminium 1

[rossibeeter]

Is any one aware of an accurate accelerated testing method for reproducing 'field-like' results with Aluminium.
Obviously pure salt spray will not and basic cyclic testing does not encompass a long enough 'drying-out' period at low enough humidity levels.

Any help would be much appreciated

 

[kenvlach]

What field??????????????????????????
What type of corrosion occurs in the ‘field’ (general, pitting, SCC, exfoliation, microbal…)?
What alloy?
What heat treatment?
What surface finish, pretreatment, coating…?

People have been trying for many years to improve the correlation between corrosion test results and long-term usage. The main value of tests is that they are standardized and can weed out ‘bad’ coatings. E.g, for anodized aluminum per MIL-A-8625F, Type II must withstand 336 hours salt spray per ASTM B117. Or, electroless nickel-coated per MIL-C-26074E must withstand 100 hours. Or, chromate conversion coated per MIL-C-5541E must last 168 hours (with no more than limited pitting as per para. 3.6).

Many accelerated tests have been devised in order to best replicate particular ‘field’ conditions. The more detailed the application, the better you can test. E.g., the Marine Corps. included abrasion with gravel along with salt spray testing for testing Al pretreatment and coatings for a new amphibious vehicle. Obviously, the more specialized the scope of the test, the better it is for a particular application, but the worse is its general applicability.

I refer you to ASTM SPT (Special Technical Publication) 1134, New Methods for Corrosion Testing of Aluminum Alloys (1992). It has 14 papers, some with discussions.

ASM has a book Corrosion of Aluminum and Aluminum Alloys, 313 pages (1999). Available:

http://www.asminternational.org/Tem...=Ecommerce/ProductDisplay.cfm&ProductID=10655

Some testing is done to develop new alloys with better properties. E.g.,
‘The Effect of Retrogression and Reaging on the Properties of the7249 Aluminum Alloy’
O.S. Es-Said, W.E. Frazier, and E.W. Lee, JOM, pp. 45-48 (Jan. 2003).
“High-strength aluminum alloys such as 7075, 7050, and 2124, which are used extensively in major structural components of aging aircraft, have shortcomings and limitations, especially in terms of their combined strength and corrosion resistance. The 7075 aluminum alloy, which is widely used for aircraft structural materials, has poor resistance to exfoliation and stress corrosion cracking (SCC), especially when aged to the maximum strength (T6 temper)…"
"The results of experimental work indicate that RRA 7249 aluminum has the strength equivalent to or greater than 7249-T6 and superior corrosion resistance."

http://doc.tms.org/ezMerchant/prodt...OM-0301-45/$FILE/JOM-0301-45F.pdf?OpenElement

So, what are you trying to accomplish in particular? Come up with a coating to exceed the warranty period…? A new alloy? A maintenance schedule?