Zinc presence in C95400 Aluminum Bronze Alloy?

[iridium77]

I am investigating the primary cause of corrosion on a large pump impeller and wear ring that is in water treatment plant service. I recovered a sample of the oxidation coating from the ID of the wear ring for ICP analysis. The levels of Al and Cu present in the analysis are inversely proportionate to their precentages within the alloy(C95400). I'm looking at both possible Aluminum leaching and galvanic activity as the primary actions responsible, however the analysis also detected Zn in amounts sufficiently high enough to be a part of the alloy.
All references for the C95400 Al, Cu Alloy that I have do not show any percentage of Zn present. Is it possible that it is present within the Cu? Any additional thoughts or observations would be welcomed. I have uploaded a portion of the ICP data for review.

 

[EdStainless]

Have you checked the water chemistry?
Are there any galvanized steel or brass parts in the system?
Given that this is a surface residue then the Zn could have been transported from somewhere else.
What material is the bowl?
How about the shaft and column?


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Plymouth Tube

 

[iridium77]

The water chemistry is definately suspect as a contributing environment. The use of chloramine in the treatment process is present, and the water pH is 8.9-9.0 The 6-in dia. shaft that is bonded to the bronze impeller is: stainless. That may also be contributing to galvanic action. The pump volute is believed to be cast iron or steel. I don't believe that there are any zinc or zinc plated parts on the system.

 

[pwtomlin]

Cast C95400 typically contains small amounts of Zn, typically around 0.15 wt % or less. This commonly comes from the ingot manufacturers and contamination from other bronzes and brasses made in the same furnaces. I do not know of any problems with corrosion of this alloy resulting from Zn content at these levels. Do you know what the source of the high levels of silica is? Si is typically controlled to a lower level than Zn in this alloy.

 

[blacksmith37]

Zinc should burn out of Al Bz at the smelter. What about the possibility that someone substituted manganese bronze for aluminum bronze ? These alloy families have similar properties. The Mn Bz contains 25% Zn and aluminum.
You can get dealloying (leaching ) of Zn from an Mn Bz.
You get much better water corrosion resistance from nickel aluminum bronze than plain aluminum bronze.