During MIG welding (built up due to surface discontinuties) of a Al-Bronze 4.25 inch shaft I found out that it was very difficult to weld it without getting lack of fusion at the edges of the weld.
After machining the shaft for about 2mm we could get a perfect weld.
Having done some literature review I found out that in Al-Bronzes you mey get effects like that if the material is workhardened, which in the case of a ship's shaft is a fact).
In this case you should preheat before welding to soften the material and then weld. In my case preheat didn't work.
The result was satisfactory only after machining the base metal and the weld it.
Does anybody have any other suggestions-explanation of the problem?
The filler metal used worked fine with the machined base metal, so I believe this is not an issue.

Valoman.