Superflux,

first off, I'll have to frankly admit that I'm way of being an expert in aluminium welding.
I heavily suspect though that there's nothing out there such as what you describe "the 309 of aluminum".

Anyway, just even last week I could meet and speak with a gentleman coming from HOBART.
His knowledge did quite impress me, since he could answer some tricky questions straight from the hip.
The alloy he was speaking of was AA 4943 and it was stated that this is the first remarkable aluminium filler wire development since decades.
Not sure about that, however, this alloy seems to have some interesting benefits to supply.

I did a research because I could recall an article written a time ago by T. Anderson and published in the July 2013 AWS Welding Journal.
Unfortunately AWS seems to suffer some issues with its new outfit or their article digitalisation respectively, because I could receive an 'Error 404' message.
That is, unfortuantely it was impossible for me to link you to this article here in this response.
Maybe you have it read already anyway.

I could however find the alloy data sheet though, see:

http://maxal.com/Hobart_Maxal_4943.pdf

Being said with reservation, but maybe this consumable is capable of significantly expanding the application frame in aluminium welding and hence maybe pointing towards a "fits all/weld all" consumable. In part at least.

As I say. Just an aluminium welding layman's opinion here.
It will be interesting thus to read from others, way more experienced in welding this material - almost being a metal.

Regards.

"Fit for Purpose"  is the key for filler selection when it comes to aluminum alloys.

As Allan mentioned there is a new wonder kid on the block which has gotten some great reviews, but it really depend on what you want with your weld.  Strength max?   Ductility Max", Color match if you anodize post weld, and more.

I've talked a lot about aluminum here on the forum over the years... Where did I get my information?  Let me tell you now :)

The link I'm dropping is a string of brief articles published over the years in "The Fabricator" all written by Frank Armao.   Frank is the best practical communicator of technical aluminum stuff I know.  He talks about filler matching, surface prep, power supplies and many other important issues.   The articles are brief and the titles will lead you right to where you need to go.

My personal go to's are 4043 for GTAW (I like the way it wets) and 5356 for GMAW (there is a bit more smut and smoke, but it can be brushed off. The 5356 is a "stiffer" wire and is less likely to birdnest, which is a benefit for folks who don't want to lay down big coin for push-pull or spool gun systems.

If you are willing to lay down the coin for a spool gun, they are AWESOME for small fab work... You can by small spools of a several fillers a low cost...  They don't hold up well in a heavy manufacturing setting (push-pull is better here).

Also I have used 5356 in a "short-whip" configuration with GMAW and GMAWP.  As long as there are no kinks in the cable and you have a fresh liner, both 4043 and 5356 can be "pushed" through a standard short whip, but there will be bird nests from time to time.

Here is the link...  You will like the read... complex problems made simple.
http://www.thefabricator.com/author/frank-armao

.

Superflux -

We use the ER4043 Alcotec (GMAW) for 6061 3/8" & 1/2" thick material  Along with the Miller 350P. Looks like a roll of nickels.
Around $80.00 for a 3/64 dia. 20lb spool.
So far it's been a real stable wire.

Thanks

4043 is the most flexable filler I know.....the JB weld of aluminum so to speak.