Hi Everyone im Rob new to this forum,Im a 50 year welding engineer trying to retire.

[weldfindsolutions]

I have been presented with a problem with Aluminium welds.A vessel was manufactured from 1703 material and welded with ER1100 however in service some of the outside welds have gone completely black but not the material. I think it could be some sort of acid vapour in the atmosphere.

 

[500e]

Welcome Rob friendly site not just welding as you will find out

 

[Brad93]

Gene Mathers at TWI would be my port of call

 

[voipio]

Pictures would help greatly.

What sort of vessel is this structure? Is it an ocean going boat, or some sort of pressure vessel in an industrial process? I cannot find any info on the composition of 1703. Can you shed any light on what this alloy is made from? Also, what does the vessel come into contact with, in the course of its "duties"?

Have you examined the blackened parts closely? By closely, I mean microscopically? The blackening may be purely cosmetic, but it may go deeper, and affect the structural integrity of the weld.

My first thoughts would be that there is some sort of surface electrochemistry involved, driven either by small differences in the composition of the 1703 material and the ER1100 filler, or by microdomains in the solidified filler. ER1100 contains up to 0.95% iron and silicon, whose electrode potentials differ quite a bit from that of aluminium. In an aqueous environment, currents will flow, creating conditions for oxidation/reduction reactions to occur, with possible incorporation of solutes present in the aqueous environment.

A bit more information would be useful. As @Brad93 mentioned, there are some very knowledgealbe people at The Welding Institute, who may be able to help.

 

[voipio]

.... some very knowledgealbe people at The Welding Institute, who may be able to help.

Knowledgeable ... doh!!!