alum weld help

[Mayhem]

Can't figure out what's going on here any ideas what would cause the tiny bumps?

[spatter]

You have a gas leak.

[WillieB]

Silica floating to the surface. Moving too slow keeps the puddle wet longer giving time for separation. Turn up the heat, move faster. The result is to put less net heat into the workpiece. Ideally, you want to heat only the weld joint. Aluminum will conduct heat away at an alarming rate. Your goal is to outrun it.

[ryanjones2150]

I have a follow up question to that answer...does the condition present in the weld pictured in the original post have an effect on the weld integrity? Such as leaking, porosity, etc...

[Bodybagger]

No. This is simply migration of silicon to the surface and it's effect on tensile strength is negligible. You can change technique, filler alloy, or both to eliminate this. This was done with an inverter welding power supply, correct?

[WillieB]

I think it influences strength in that it is evidence that you were there too long with heat. Aluminum conducts heat away. We don't want heat other than in the joint. Take too much time, more heat migrates past the weld joint. HAZ is larger, temper is lost in a wider area. A greater volume of metal will shrink as it cools, causing more distortion.

[Bodybagger]

Let's say you cut a transverse coupon to run through a tensile test. The middle where the weld is has a filler with a rated tensile strength in the annealed condition of around 27ksi and the rest of the coupon has a tensile strength of 42ksi, except where the temper is blown out in the HAZ. Does it matter how wide the HAZ is? No. It's still going to break at the CL of the weld. So does this surface imperfection affect strength? Nope.

[H80N]

Can't figure out what's going on here any ideas what would cause the tiny bumps?

I would ask.. what alloy was being welded..?? and which filler was used..??

weld parameters??.. shield gas.. tungsten etc..??

not enough detail in the pic for me to see what is going on..

is it alloy precipitation or outgassing..??

[Tryagn5]

Let's say you cut a transverse coupon to run through a tensile test. The middle where the weld is has a filler with a rated tensile strength in the annealed condition of around 27ksi and the rest of the coupon has a tensile strength of 42ksi, except where the temper is blown out in the HAZ. Does it matter how wide the HAZ is? No. It's still going to break at the CL of the weld. So does this surface imperfection affect strength? Nope.

Agree with everything in the above post, however where strength is really lost in a real world test, is vibration/flex, as the hazed area will fail with much less input then 27ksi, when vibration is introduced. All metals exhibit this, how many welds i have i seen fail, very few, but next to the weld, where the metal was overheated, undercut, or poorly fitted is the failure break.

[H80N]

From Miller "Ten Common TIG Problems: A Visual Guide "

Figures 2B and 3 – Weld Graininess

" Figure 2B shows the way an aluminum TIG bead should look. Figure 3 shows a bead with a grainy appearance, which is typically caused by filler metal problems. For instance, a 4043 aluminum filler rod from one manufacturer may have different properties than a 4043 rod from another manufacturer. The welder (if the application permits) may need to adjust filler brand accordingly. The rod may also be defective (too much of a certain ingredient). The welder may even have the wrong type of filler rod, such as 4043 filler instead of 5356 filler.
Prior to welding, always check the filler metal type and remove all grease, oil and moisture from the surface to prevent contamination."

http://www.millerwelds.com/resources/articles/common-TIG-GTAW-welding-problems-visual-guide-graphic

Just a little food for thought on the subject....

point is... that there may be several causes for similar defects..

[ryanjones2150]

alum weld help

At the drag car shop, I have a big transformer machine...never had this problem. In my shop at home I have an inverter welder...and also the only time I've had similar looking welds to the original post. The base metal was unknown, the filler metal was 4043 I think? pure argon, 2% lanthanted tungsten. I can't remember the AC balance and freq, but I generally use settings very close to what the transformer machine has in the drag shop because it's what I'm used to and I'm not solid on the benefits of changing all the whiz bangs around for different applications. I'm guessing some of those fancy dancy settings could effect the outcome. I need to spend some time really studying up on that stuff.

[H80N]

Are you by any chance the same Ryan Jones that built the "TOASTER" 65 Nova..??

http://www.dragzine.com/news/ryan-jones-nearing-the-finish-line-on-his-outlaw-8-5wild-street-65-nova/

Nice work...

[ryanjones2150]

alum weld help

Ha! Nope. Nice car though. Ours is WAY uglier than that machine! I have to holler at the looky-loos in the pit, they always want to come and put their hands on the ugly beast that sounds and runs so awesome, they're gonna wipe my dirt off! They just don't realize that layer of dirt is a highly scientific, anti-drag, aerodynamic coating that's taken years to develop. Who knew a 4200 lbs car that was previously sitting in a put of junk could run in the nines? Drag Week here we come!

...now back to aluminum welding....

[H80N]

Ryan

having seen that condition in the past and never getting an answer that fully satisfied me.... I sent an inquiry to Galen White at Hobart Metals...

"Galen
Hope all is well with you and yours
Would you be so kind and read this thread.. and give us some insight into possible… strength degradation etc etc

http://www.millerwelds.com/resources/communities/mboard/showthread.php?34643-alum-weld-help

Is this Silicon precipitation..?? or other alloying metals..?? Copper..?? Mag??...
Long and short term effects.. microcrystalline…
Filler metal suggestions..??
Regards
Heiti"


And this i what I got back from Galen


From: Galen White [mailto:[email protected]]
Sent: Monday, July 27, 2015 9:20 AM
To: Heiti Narma
Subject: RE: silicon precipitation in aluminum gtaw welding..???


Hello Heiti,

This is a condition that I have been trying to get an answer to for quite some time. So far I have not gotten an answer that I’m happy with. Actually, last week before your email came in our weld technician brought me a TIG sample that looked like this and I had him shoot a radiograph of it to see if the spots were subsurface porosity or not. They are not. You can see in the pictures below that there is some porosity in the root of the joint but the surface ‘granules’ don’t line up with any pores in the x-ray film.
Every time I’ve seen it, it’s been with 4XXX filler metal (never 5XXX) but unfortunately I don’t have a definitive answer for you. I will keep digging and get back with you as soon as I get an answer.
Thank you for your patience.

[USMCPOP]

There must be an explanation ...