Porous aluminum welds?

I've been welding for a while, and can lay down a nice sexy aluminum bead... some of the time. We've had alot of problems with my aluminum welds leaking though, and i don't know what the problem is. It's usually 6061 or 7075 and welded using ER5356 rod with pure argon and pure, clean tungsten. i can pull the torch away at the end of the weld to eliminate the little divit thats usually left, but there are still leaks in other spots. Any Ideas? I don't think its my technique... but I've been wrong before.

Thanks,
Eric

 

Hard telling without seeing your Beads. What technique are you using to apply the filler? Personally, I always had better luck stabbing the filler in and out of the puddle rather than just flowing it in constantly. I get less porosity and better penetration that way, and IMO it looks better.

Other than that, I always use a SS Toothbrush on the joint right before welding, I run the filler rod through Scotchbrite if it has any dirt or corrosion on it, and I always leave a gap when I tack it up. For example, a "nickle" width gap on 1/4" aluminum, reducing the gap proportionally as the material gets thinner.

I also tend to run hotter and move faster on sheet aluminum. At higher amperages, with increased travel speed, you retain penetration, but put less heat into the surrounding metal, thereby decreasing the warpage in the surrounding metal. That doesn't work so well on heavier aluminum however, it needs to be pre-heated to keep the weld from cracking, and the slower travel speed helps to maintain that heat.

 

First guess is contamination. Second is overheating (boiling) the metal. Hard to tell without a picture to look at.

Are you wire brushing your parts just prior to welding??? Are you using a DEDICATED stainless steel brush??

Are you sure your Argon line isn't sucking air anywhere??? *that bit me once - drove me NUTS until I found it*

 

I use an gas lens collet body. That may not be the correct name, but it's the type of collect holder that has a mesh screen around the tungston and is larger than the standard collet holder to better "mix" the argon...... mix it with what? I don't know.

Don't jack the argon flow too high.

I also use a larger cup to cover a larger area of the weld with shielding gas. The threaded end of the cup has to be bigger to go over the gas lens, but I also use one that's larger on the outlet side.

When you got your TIG, did you buy a whole box of cups only to discover you've never broken one?

 

And, I use a stainless steel brush to clean the parts to be welded. Voices in my head have told me that any other type of brush will contaminate the brushed surfaces....... pass that thing over here.

 

i do have a dedicated stainless brush that I use, I was going through to take some pictures and the ugly ones are the ones that leak more often, what's proper procedure for that? I've been grinding them down if its important and going over them to make them look better. The last leaky one that happened was on some master cylinders we had machined, there was an access hole that needed to be plugged and we made a little plug and I just went over it to melt it down and added a little filler, I didn't leave any divit or anything... but it leaked. All I could find was pictures of my shitty welds that did leak, and a good weld that I haven't tested yet... but there's been some fine looking welds that still leaked, I think those parts have been tossed since then though. Picture #3 is one of my "good" welds that someone polished poorly.

I know thats not much info, but maybe you can tell me what's wrong from the last picture... thats how they look most of the time. Its on .063 tube.


http://img.photobucket.com/albums/v237/Flexicoker/Misc/weld1.jpg
http://img.photobucket.com/albums/v237/Flexicoker/Misc/weld2.jpg
http://img.photobucket.com/albums/v237/Flexicoker/Misc/weld3.jpg

 

you have to remember that most aluminum car bit (i.e. intakes, bellhousings, valve covers, etc) are cast. cast by definition is dirty metal. your welds may not be the problem at all.

 

Looks to me like your doing a lot of starting and stopping. Are you cleaning the weld area everytime you restart? The Argon gas will leave a film over the weld, if you don't wire brush it before you restart you are traping that film in your weld puddle creating a void. Also looks like your puddles are aways apart, you either need to slow down or feed the filler rod in faster. I hate welding aluminum...Gene

 

it's hard to tell, but in photo #3 it looks like you have some "crows feet", or heat checking. you could try turning the machine down a tad, and adjust your speed to compensate.

 

This is correct. Any kind of cast aluminum can cause problems with porosity, especially rough cast parts like Bellhousings. In the rougher parts, sand and other impurities are embedded in the material, along with tiny air pockets.

What I usually do on something like that is to turn the grinder edgewise and groove the area to be welded. This will get the root of your bead well below the surface, and away from most of the impurities. You may still have some porosity along the edges of the bead, but the root will have a better chance of being porosity free.

On pieces with a lot of mass, like bellhousings and master cylinders, I would preheat the part. Aluminum tranfers heat so fast, it can easily crack a weld as it cools off.

I learned that the hard way once, welding 3/8" plate aluminum. I had an 1/8" gap, plus beveled the joint over halfway through the plate. I preheated the area around the joint, but not nearly enough. As soon as I raised my hood after welding, I watched it crack right down the center of the bead as it cooled. Like slow motion...

I ended up having to get another guy to stand there with a Rosebud. As soon as I raised my hood, he had the rosbud on the joint keeping it from cooling too fast. It worked. The piece has stayed together for about 6 years now.

 

I don't weld any castings, its usually fairly virgin tube/sheet or machined parts. I am starting and stopping alot and I didn't know to wire brush so I tried that last night on some intake tubing. It should only see about 15 psi or so, but leaks=lost hp. I also went alot slower on the last piece I did, and it looks alot nicer. Thanks for the tips guys. I guess it was probably my technique, haha. I figured I'd done enough steel that I shouldn't have that problem with aluminum... whole different animal.

 

Yep... slow down. Use the lowest heat possible.
Don't jump on the padal and start throwing filler in, either. Let the base matal get flowing, and as long as you have your heat low enough, you can stay there and let it melt, without boiling it... and don't add your filler until the puddle is ready for it.

Try tightening up your beads a little, too. If you jump too far, the spot behind you cools too quickly, causing the bead to pull away from the base metal at the root. Plus, you're starting on cold metal each time. Follow the bead, don't make it follow you.

If your wire is too fat, it won't melt quickly enough, or, when you pull it out, you'll leave a little hole behind. I weld almost everything with 1/16" wire...
On the same coin, if you hold the tip of your wire too close to your arc, it'll be so soft, that when you go to add wire, it'll drop off before you can get it to the puddle. Get in the habit of pulling it out away from the arc.

You might be dragging crap into the puddle from the other side, also.



JOE

 

I don't think this has been mentioned yet, but 7075 Isn't typically weldable, I think it has alot of zinc alloyed into it which causes cracking problems and contamination looking weld problems.

What size electrode are you using for this tube? I usually try and use the smallest electrode possible. If its too small it will continue to make the ball on the end of the electrode larger and larger. But a smaller electrode has a smaller heat affected zone and tends to put less heat in the part.

The stainless brushes are cool, but I prefer soaking my parts to be welded in an aluminum cleaning solution that I bought at the welding supply store. I forget the name, but it's blue in color and a mild acid that removes the surface oxides and contaminants.

How old are the filler rods you are using? If your filler rod is old and oxidized you will introduce contamination into the weld everytime you add filler. I've layed a clean rod down on a dirty bench and then proceeded to then ruin the next weld with the now dirty or oily filler rod.

What's the condition of the o-rings on your torch body and or back cap? damaged or missing o-rings will suck oxygen in and dilute or contaminate your argon flow. Hope this helps, keep us posted...