Selective Corrosion of Al alloy casting

Hello Group
Has anyone ever come across selective corrosion (leaching) of the Al phase from a cast Al Alloy? What's left behind is a skeleton of primary silicon needles in a matrix of
black corrosion product. It looks very similar to graphitisation in gray iron, but i cannot find any reference to it anywhere in text books or on the net. Any help appreciated.
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Dave Herbal wrote:

Selective leaching (dealuminification) is known to occur in aluminum bronze alloys. I haven't heard of it in aluminum silicon though. What is the environment? acid or alkali, etc?
Google it!
PIttsburgh Pete
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I think this is the usual corrosion pattern of aluminium/silicon alloys, aluminium being much more active than silicon. The question might be under what conditions it occurs. I have seen it many times on castings used underground with bacterial corrosion the usual direct cause
bob
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in article snipped-for-privacy@clear.net.nz, Bob Redfern at snipped-for-privacy@nospamparadise.net.nz wrote on 13/3/06 9:36 am:

It's a cast bowl from a vortex drain of a compressor air drying system. Analysis of the corrosion product showed high levels of Al, Cu and S. Apart from that we know very little. I'm glad you've seen it before Bob, I've been doing failures for 12 years and have never experienced it, and I still can't find any reference in google. I think that normally you may get attack of the Al first, with the Si falling away afterwards, but i've never seen the Si preserved perfectly in the black corrosion product before.
Cheers
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any chloride in the air, in the form of salt water or such? whatever is washing the Al away is pretty aggressive.

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