Need to get some aluminium welding done on my horncasing, (some fillets on the bottom for a Spanish turning mudguard) how fussy is cast ally about what it welds to?
Does it need cast ally the same, or is sheet ally OK, what about duralumin?
"cast ally" is a big group of metals. Its ease of welding depends on which you have. Not tried to weld the item you mention - and italian, spanish, indian etc etc may have used different alloys. What often worked for me, was to lay a small bead along the edge to be joined, this brings out any sh!t which if necessary you can clean off, then weld on to that. TIG or MIG should work fine, if its very thin a piece of copper to support the back helps stop droop or sag.
Most Al that comes in flat sheet should be ok - its hardly structural is it? 3000 series sounds fine. The less fancy the better really. If you have access to a chunk of decent casting of similar thickness, then you could use that, but its probably easier to find a bit of flat sheet.
Duralumin was a proprietary grade and has been discontinued, but I think folk use the name for similar grades. It has, IIRC, quite a high percentage of other metals in its composition like iron and copper, its these that may cause difficulties.
use TIG on ac as positve and negative cycles add heat to the weld pool and the other cleans the oxides from the weld, also the ac kind of shakes the oxides out.
do not grind the weld prep - this will just smear the oxides over the surface - you need to remove them by mechanical action - either a rough file or cutter bit (router/dremmel etc)
the ali melts a lot lower temp than the oxides (oxides approx 1500 deg c opposed to approx 655 deg c)
degrease weld wire and if you really want to go the full monty take oxide layer off wire just before welding (see above for removal)
some tig sets you can adjust the positive/negative cycle for more cleaning action or heat input
finally - watch the weld pool as it is very fluid (runny) and due to the high coifficiency of thermal conductivity of aluminium the heat will quickly dissipate from the weld area so watch out for lack of fusion
