Corrosion of Aluminium

[Daz8576]

Hi all

I'm new here and couldn't find what I was after via the search so hope someone can help clarify a query I have.

I read a thread on another forum with interest as an aerospace corrosion expert claimed that aluminium would corrode at the same rate when subject to a salt rich environment i.e. road salt, regardless of grade.

I'm no expert but from my limited understanding thought the whole point of alloying was to elicit a specific kind of performance (be it strength/corrosion resistance etc). I realise that salt will ultimately corrode any grade of aluminium but thought different grades would possess varying amounts of resistance.

My query is regarding untreated aluminium i.e. non anodised/coated.

Many thanks in advance for your help.

Regards

Daz

 

[CoryPad]

There are many qualifiers to corrosion resistance, but a general statement can be made that corrosion resistance due to chloride ion varies from one alloy to another. For example, commercially pure Al (like alloy 1050) has much better corrosion resistance than alloy 7075-T6.

 

[Daz8576]

Thank you CoryPad

I did think it a little strange when I read the suggestion that the rate corrosion was irrespective of grade. It seemed to go against everything that I've learnt and is contained within the MIL Handbook/MMPDS and other literature. However as corrosion is not my specialty took his word for it.

Perhaps there are other situations that make grades irrelevant ?

The situation I'm referring to is the accumulation of salt/grit on aluminium components during winter (in the UK).

 

[swall]

Much of the published information is based on ASTM B-117 (or similar)salt fog testing on various aluminum alloys, and the corrosion resistance is ranked A, B, C,etc. This is pretty vague and if specific corrosion resistance information is needed for a specific application one needs to either consult the aluminum suppliers or perform their own testing.

 

[strider6]

The series 5000 is a "marine grade" that ,means that is suitable for exposure to marine atmosphere and also to seawater.

http://www.azom.com/details.asp?ArticleID=310

http://aluminium.matter.org.uk/aluselect/02_corrosion_browse.asp

S

Corrosion Prevention & Corrosion Control

 

[Daz8576]

Thanks again.

It was mentioned that 5000 series was marine grade but the chap insisted that it did not matter as the type of environment that was being discussed was the build up of road salt and the drying off cycle that led to corrosion - regardless of grade (how confusing).

Not that I'm doubting you at all. It just seemed odd that he was dead set on suggesting it did not matter what grade it was. I think the suggestion (from the opposition) was that corrosion would occur but the rate of corrosion would be markedly different.

Anyway many thanks for the links and info.