It's possible to weld a pretty AL weld without hardly any spatter using MIG but doing it for hours on end, or changing positions during a weld make it very, very difficult to maintain the conditions required. It's just entirely too picky. One of the biggest drawbacks for structural work using MIG is cold start. It does not matter if the material is pre-heated or not, the first portion of each weld is cold with poor penetration. The same is true with MIG on steel but it is just never discussed. It is an inherant problem with the MIG process.
I have successfully welded AL with MIG - it can be done under certain sircumstances and there are situations where it is definately the way to go - I do not disagree.
I, like many others, weld mostly structural - 6061 and 6063. Welding 5053 is a different animal and the 5000 series stuff welds a bit better, but the cold start, soot, spatter and inconsistency issues associated with MIG simply offer too much hassle to consider MIG for most situations where the type of welding varies - like in a home shop or a job shop.
Let's put it this way - I can guarantee a weld with TIG - first time, every time. I can join 1/2" to 1/8" without blowing out the 1/8" in a lap, **** or fillet configuration - first time, every time. You just can not do stuff like that with MIG without a few test runs to tweek your arc position, wire speed, amperage, voltage and speed. Then when switching between a lap and a **** joint with MIG - all of your settings are different. Too much of a PITA. Additionally - to those who say it is slow - BS. TIG is only as slow as the operator. It is easy to run a TIG bead nearly as quickly as a MIG. TIG is faster than MIG when you factor in spatter and soot removal for most conditions. A boat hull?? No. A dump body?? No. These are jobs that are suited for the properly set-up MIG process.
Now - MIG for higher amp situations is great, but for lower amperage work - as stated previously - 3/8" or less - do yourself and your wallet a favor and consider TIG. Yes - you can MIG 1/4" and even 1/8" but the consitency and appearance are not going to even be in the same zip code as a TIG weld. And you can forget a **** joint for the thinner stuff. A fillet weld on 1/4" is fine - but you still have spatter and a cold start which will eventually begin to fail.
If you want a pretty weld TIG is absolutely the way to go. When you are done with a TIG weld - you are done - no clean up, no cold start, no soot, no spatter and a LOT more control.
Sorry for the babble.
Scott
