As Van Morrison would say.

"Now were getting down to what is really wrong"

Two things I see right off the bat.

During the several hours in the oven, those oxides you removed have grown right back..  Surface prep for aluminum (weld rod and componant) that is as critically inspected as you describe must be cleaned immediatly before welding.

Balence control
The 65% EN balence you are set at with your inverter is equivilant to your old Synchrowave being set at 10 of 10 on the Max Pen dial.  Back off the balence another 5 or 10% and I think your porosity will be eliminated.

Your combinaiton of reduced current on the EP side of the half cycle and 65% dwell time on EN are simply not providing enough Cathodic Bombardment (cleaning action).

AC Frequencies above 220 Hz are only an annoyance, and the pulsation (what ever your high and low are set at) won't hurt, but with your current balence control settings and oxide removal practices it won't help either.

As nice and Flexable as a "True Squarewave" Asymmetric inverter power supply may be.. The fact is that 99% of X-ray quality AC GTAW welds will be made within the paramater threshold achieved by an old transformer rectifier like Synchrowave or Precision Tig and it's "traditonal squarewave" AC power delivary.

Its not a gas problem (I bet)...   All the Kings horses and all the Kings men cannot overcome basic AC arc physics and the need for good cathodic etching.

Edit:

Your garden variety transformer rectifier traditional square wave power supply will produce 68% EN when set on max penetration... Lincoln 68% EN,  Miller 68% EN,  Esab 68% EN, brand doesn't matter.  With that traditional square wave set at max pen, will you have sufficient cleaning action to make X-ray quality welds in aluminum?  Not likely in most circumstances!

So in essence you started your procedure at an AC balence setting that was not very likely to produce sufficient cleaning and then you starved it another 60 amps with your Asymmetric 140/200 amplitude setting.

Is it beginning to come clear?    It's a tough subject to get your brain around for the first time.

So why did we buy an $8,000 dollar inverter welding power supply that can go beyond that 68% EN all the way to 99%?
Good question!

The sales guy said it makes smaller fillets and stirrs the puddle... Ok, it does..  But the X-rays aren't  lying on those smaller weld profiles.

Dynasty 350 also has the unique ability to produce *Triangular* wave forms...  Nice whiltle/bell... and very good for lighting a room, but don't try to use it to join two pieces of metal  :)

To get a consistant X-ray quality Alternating Current GTA weld on aluminum... You must sufficiently etch the metal with EP and there is no way around it.   Now your $8,000 inverter has several ways around this issue..  But unfortunatly there is nothing published regarding succsessful standard practices for Aysemmetric AC power delivary on aluminum.

One way around the issue is to run your EP for a radically short dwell time.. 2-5% EP but at an equally radical amplitude.  Remember It doesn't so much matter how the EP is delivered, as long as it gets there in sufficient amounts.  A short blast of high amperage EP will do more than any pulsation/stirring your Miller rep ever suggests.  This kind of procedure (Asymmetric True Square Wave AC power) takes plenty of trials to nail down when you take it near the limit. Most of the time its just simpler to scale back to what you know will work rather than trying to create some designer wave form to do the same job a 1988 Synchrowave can do as soon as you slap the part on the workbench.

It becomes very easy with one of these fancy machines to go right to the limit of high performance and take that next step over it into the territory of diminishing returns....  Too much of a good thing etc.

aerowelder,

first off, thanks for the information you have provided!

And as I thought, might there ever be a better explanation or bulk of excellent recommendations as even that what has come from Lawrence and... has additionally been confirmed by Tommy?

NO!

I would entirely agree with Lar when he says:

"During the several hours in the oven, those oxides you removed have grown right back..  Surface prep for aluminum (weld rod and componant) that is as critically inspected as you describe must be cleaned immediatly before welding."

and:

"Its not a gas problem (I bet)...   All the Kings horses and all the Kings men cannot overcome basic AC arc physics and the need for good cathodic etching."

Even as well the superior explanations on what the welding power supplies are capable to perform were an enjoyment to read. Truly excellent...

I humble mean to say that everything you have described is 100% professionalism in work and everything what Lawrence has stated is 100% of professional technological advice based upon immense expertise.

I am quite sure when following Lawrence' recommendations the problem will dissappear faster than it could emerge.

The idea with the hose materials might have been an "option" if the conditions were somewhat different from those ones you have reported. And I am certain if the hose materials were the reason for the porosity you surely would have observed "porosity problems" more than once since using this manifold system, serving so many workplaces with shielding gas.

And this finally would confirm the very first statement coming from Milton who said:

"If you use 99.99 UHP argon you shouldn't have to!"

It would be great if you might keep us in the loop for any progression in this very interesting topic*...

Best regards,
Stephan

* ...very interesting thread. Have learned a lot! Thanks for that!

Stephen,

I make no judgement at all on the argon purification topic. It's way above my paygrade :)

My personal experience/observation has been that "welding grade gasses" do the job when they comply with specifications.  GTAW of Aluminum is like a Canary in a coal mine!  If the gas is bad the results are usually evident immediatly... Refractory alloys and Titanium are quite a different thing however.  The amount of oxygen or nitrogen (the most common contaminants by far) it takes to foul a titanium weld is far far below the threshold of contamination it takes to make a change in the surface color of the weld... This fact applies for both Alpha case and for the weld depth entire. A Titanium weld can be embrittled to the point of non conformance with a perfect visual appearence and perfect X-ray result. So I can see the motivation of an OEM to desire extra precautions in some specific instances.

I suspect the in line >gizmo< I mentioned that we used may have been a device that was a safety precaution stipulated by an OEM against some contaminant that might come during switching of bottles or filling of dewers.

OK, so a while back I was helping figure out a similar problem.
We didn't have so much of a porosity issue, but excessive discoloration of shielded SS autogenous GTAW tube welds.
At the time we were using 99.999% pure certified gas from a bulk liquid storage tank in which we received a purity cert from the vendor for every purchase, plus we were having a third party test the gas as well to validate purity.
However, when we had the gas tested from various weld station throughout the plant, we found slight moisture and oxygen impurities. At this point we started thinking about buying one of those expensive filters to add to the system.
I kept looking for a cause and the determining factor was that the further down the line from the bulk tank we got, the impurity level would rise as well.
Then I looked up at our manifold system and actually "saw" it for the first time as a carbon steel screw pipe manifold. That was one of those moments where I smacked myself in the forehead and said wake up stupid... It seems that the tiniest leak in a fitting not only allows pure gas to escape, it also allows impurities to enter. To make matters worse, the longer the manifold is allowed to sit without being used (weekend holidays etc.) the worse the contamination becomes as more moisture is allowed in which starts corrosion, which either worsens or makes more leaks.
Anyway, we ran some SS tubing straight from the bulk tank connection to the auto welder stations and Viola!, no more problems.
Also let me point out that during this time I learned that the green rubber gas hose typically used to connect a welder to a bottle or manifold absorbs moisture at such a rate as to effectively ruin gas purity for SS autogenous welding and Titanium welding. HDPE hose, if any is a must.

Tim