Contamination/smut in aluminium weld

[Brad93]

Currently doing a little aluminium tig project, seem to be having an issue with some stubborn contamination of the weld, more prominent on outside corner and butt joints than fillets. Specifically speckled black defects.
Have cleaned part (dry stored aluminium) and filler rods with acetone.
Have used a carbide burr on all edges to take off the oxidation/slight marring from the guillotine.
Haven't used a wire brushed or scotchbrite as want this to look good cosmetically.
AC balance I have changed between 30-40% EP with no real improvement.
Frequency 100Hz-120Hz
Argon 7lpm #7 stubby gas lens.
I'm starting to suspect an air leak somewhere between the gas solenoid and the torch. Reg on bottle holds pressure for days.
The only thing is it is happening with both a Lorch torch and a ck torch.

Not sure what else to try. Never had such a persistent issue with contamination. Will get more pics tomorrow.

The only other thing I can think is my wire and base metal aren't compatible? 5152 Base 5356 Filler. Too much magnesium?

I'm going to cut some 1050 tomorrow to see if I have issues with that using 4043. Only problem is that material got left outside although undercover and now has some water marking/thicker oxide layer.

 

[Brad93]

Not sure if you can make anything out on this.

 

[hotrodder]

Won't be the flavour of wire, 5052 or 5251 isn't that fussy about filler wire and the wrong flavour is more about poor matching with regards to corrosion resistance or ductility etc than crud in the weldpool

First thing i'd do personally is grab an offcut or two of the same material and see what, if any, differences tickling it with a stainless brush makes.
7lpm shouldn't be excessive for butt welds but i'd expect turning the flow down a bit to improve shielding on outside corners
Doubt it'd make a difference but have you tried tightening up the spacing i.e. less wire more frequently? I get it's not what's happening but in the 2nd pic it kinda looks like crater defects but without craters if that makes sense

If none of those make a difference i'd be a doing a spot weld test on some stainless and if it doesn't come out colour free i'd be leaning toward a tiny gas leak somewhere

 

[Richard.]

Rarely do I ever scrub Alu either but a wipe down of the filler and joint with an acetone damped cloth makes all the difference sometimes. Even a bit of metallic dust stuck in the corner of your set joint is more than enough to play havoc with your pool.
Outside corners are quite common for contamination due to there open nature of allowing your shielding to escape. Turning up the gas can make this worse sometimes. I had this problem a long time ago causing a lot of frustration with little burnt marks (very different to your case) appearing on the weld. Turned out the filler was at fault in the cold work shop. Possible moisture ingress not sure exactly but since then all my Alu filler is stored in the warmth and has been problem free ever since.
I always keep an old soft tee shirt and give every thing a very quick wipe before strike up* Probably wasting my time for most of it but contamination issues don't tend to cause me many problems so no reason for me to stop.
* make sure if your doing this on the joint your burrs are removed or you'll end up rubbing the fine bits of fabric into the joint again making it worse.

 

[Jim Davey]

Try "sealing" the back of the open corner joint with something like a square copper bar and as said, make sure your filler is cleaned as well as your base metal, also keep your hot filler end in the gas shield once you start so you don't add oxidised filler every dab and keep a short arc.

 

[Brad93]

Keeping the filler nice and tight so should be well shielded. I will use a lower gas flow with a smaller cup and see if that has any effect.

@Richard. what you're saying about filler and cold workshop may well be the case. I keep my rods indoors, and just a dozen lengths or so in separate tubes in the workshop. I'll grab some fresh stuff.
All the edges have been cleaned along the length with a carbide burr kept for aluminium and given a tiny deburr/bevel along each edge. I have had them random burn/brown scorch marks on the weld on this.

@hotrodder i have some titanium so will snip a little piece off and spot test for gas leaks/contamination. Then will do some test coupons in 5251 and 1050 and get some better photos. Will also test with and without wirebrushing.

Sadly Jim I only have a decent amount of Ali chill locks and haven't built up much in the way of stainless or copper ones yet. I get what you're saying though everything I used to weld at my tig job had an bang on for size fixture as backing to control distortion, gave you perfect penetration on outside corner joints every time as long as you used enough heat.

Thanks for your help guys much appreciated. Will let you know how I get on.

 

[Brad93]

Right no problems with any of the torches on Ti or wire brushed 1.5mm thick 1050. One thing I have done is give it a bit of preflow gas as I was getting dirt on starting the arc. 0.5 seconds of preflow on the pedal has cured this. Time to play with some 5251.

 

[Jim Davey]

0.5 is a bit on the mean side, it's barely long enough to push 4 metres of air out of your torch. 1 sec is my usual minimum.

 

[Richard.]

Yeah Jim is right. And if your running a single stage reg where start up surging is happening I'd suggest more like 1.5-2 seconds ideally because you want the flow rate to stabilise before hf kicks in.
2 stage regs 1 second is plenty.

 

[hotrodder]

FWIW i've used about 1/2 second preflow with a 4m torch for years with zero issues. With exotics i sometimes* increase it but for everything else it's sufficient imo. While the flow rate won't have stabilised properly can hear the initial 'burst' before the arc cuts in and feel if it before the HF gets you if you zap your finger or whatever. I used to increase preflow time for stupidly thin stuff for arc striking accuracy but surge reducing dodads and/or multistage regs are a better way

* 'Cause pre flow time is in the 'hidden menu' that's only accessible machine during power up on mine if it's a small job i usually just tap the pedal/button quickly to activate the gas and then strike up while the post flow is going

 

[Brad93]

Same with this machine i'm using hotrodder. Its a bit of a pain because to get to the hidden menu you have to hold the two job buttons at the same time and with gloves on if you slip or don't press them at the same time it changes the job and you lose your settings. Only little discrepancy with this machine and god its a minor one. Ive taken to just rewriting over job no. 2 every time i get the settings where i want them for that work.

 

[Brad93]

I need an Elga reg for sure! However ive spent enough on the TIG lately I need to earn some keep before anything else is purchased.

 

[Richard.]

Doesn't have to be elga or expensive

 

[Shox Dr]

Harris gas saver, brilliant bit of kit. I set the saffire to around 40psi, then the harris so the flow meter will just read 15lpm fully open. The Harris has saved me tons of gas. You dont get that initial burst, as HR says.

I found if I purge the leads (8mtr) before I start for about 10secs, I don't have any problems that day.

 

[Richard.]

Harris gas saver, brilliant bit of kit. I set the saffire to around 40psi, then the harris so the flow meter will just read 15lpm fully open. The Harris has saved me tons of gas. You dont get that initial burst, as HR says.

I found if I purge the leads (8mtr) before I start for about 10secs, I don't have any problems that day.

View attachment 92961

Nice. Does that add a secondary stage to your reg shox.
GasIq do one similar but with a built in flow tube. As you can expect from Elga though beautifully made with a heavy price tag.

 

[Shox Dr]

Yes, and its adjustable unlike 2stage regs

 

[Richard.]

Yes, and its adjustable unlike 2stage regs

What's adjustable?

 

[Shox Dr]

The harris. A two stage reg has two stages but only one means of adjustment.

Underneath the brass domed nut is an grub screw you adjust for oulet pressure

 

[Richard.]

The harris. A two stage reg has two stages but only one means of adjustment.

Underneath the brass domed nut is an grub screw you adjust for oulet pressure

Ah I see. Yes mine only has one adjuster on the main out going and a separate valve for the purge.
What's the benefit of having an adjuster per stage. I've not seen that before.

 

[Shox Dr]

As I understand it... a single stage reg has bottle pressure one side and user set pressure the other, this can cause the surge when you pull the trigger. To help stop this a dual stage has two chambers, but it still suffer surge.

By throttling the reg to just above max torch pressure, and fitting and reg (The harris) in line, this reduces the back pressure dramatically, thus reducing surge, and so gas.

Some may scoff, but if your main line of work involves lots of little tacks, all that gas adds up.

(I've just been working for a local co, Doing the same amount and type of work as two other guys, a bottle would last days longer than theirs