I've used Devcon Aluminium putty on a blended trumpet base I made for someone (on here possibly) - impressive stuff.
Expensive at £80, but I can see it on ebay for less - probably out of date, but I don't think I would overly worry about it - it seems to keep OK.
http://www.ebay.co.uk/itm/Devcon-Alumin ... 33970b1f64
Actually the above one isn't out of date, so it is a bargain price. I used some to "fix" (read unspeakably bodge) a sump plug in! Perry would be proud of me..