Ali-MIG 5000-series Al-Mg - wire dias 1.2mm vs 1.6mm

I've gone for an Ali-MIG (Aluminum-GMAW) welding machine.

Lincoln Foundation book says all 1/16" = 1.6mm (apart from bigger for bigger size). I have only used 1.2mm wire - 5356 - some 5183.

At thicknesses of Ali plate of like 10mm and 12mm, reckon about

By area ratio - which is exact guidance for steel - would be for 1.6mm wire (/ (* 14 9) 16e0) ;; 7.875 ;; m/min (/ 7.875e3 25.4) ;; 310.03937007874015 ;; 310ipm

AI searched for me - it says

• 1.2mm more penetrative
• 1.6mm is softer more spread-out arc

With 1.2mm wire I wondered if fillet corner fusion was too much (!). On T-fillet 10mm thickness definitely and Al-Mg (5000-series),

• edges plasma-cut
• plate much abraded (it was a recovered floor checker-plate)
• which I wire-brushed with a steel brush (no stainless wire brush) There was quite a swirl of solid detritus circulating around at the leading edge of the weld-pool, and I got a sense I was slowing-down the weld to let it float-out and ensure fusion.

I tentatively thought

• I run much quicker on clean plate
• I suspect the very penetrative arc was melting-out contaminants in the contact between the terminating plate and the continuous plate in greater quantity?

I can macro-etch marine-grade Ali, to inspect the outcome. I do want to avoid equipping up with MIG-torch / GMAW-gun which I don't use. Hence - anyone know the arguments on this and can advise?

I did break a weld in the wrong place and it took seemingly too little effort. I suspect the slowed run-rate gives coarser structure which is less strong (?). I suspect I need to weld fast(er). I like the idea of uniform penetration across the weld legs, and running fast...

Anyone tell me if I can weld Al-Si 4000-series with a standard "push" wire-feeder if the wire is 1.6m / 1/16" ? With slippery liner - PTFE or HDPE? (only met HDPE). I have never MIG'ed 4000-series before.

Regards, Rich S