I managed to arc weld some aluminum effectively. I wanted to share the results with fellow enthusiasts. I used a Miller XTM 300 CC DC inverter power source. It is a very nice machine that I came across for a song at a going out of business sale. It will do DC arc and TIG (with the proper kit). I was confounded trying to use my "buz box" AC arc welder. It kept acting like there wasn't enough amerage to get the arc started. Finally I read some information that pointed to the type of machine as the culript rather than the rods, workpiece, or another factor. Using the XTM I was able to weld aluminum rather effectively. I tested and practiced on an old thermostat housing before attempting anything important. Once I had a good grasp on the technique I repaired a transmission case with a broken ear, and found the repair to be just as strong as the stock, undamaged ears.

Here are some tips for effectively arc welding aluminum:

1.) Cleanliness is of paramount importance. You can usually weld steel right through the mill scale, over mild rust, etc. Aluminum must be prepared carefully. All grease and oil must be purged. Use somthing that will evaporate completely like Brake Clean or Acetone. Then sand, grind, or blast the area to be welded. Finally, scrub the area to be welded with a clean stainless steel brush used only for this purpose. If the brush is dirty it will contaminate the weld with mild steel particles or dirt.

2.) Preheat. Especially castings and thick sections. An oven or propane torch is prefered. Don't use an oxy/acetelyne torch. It will contaminate the aluminum. Look for at least 200 degrees farenheit, but up to 350 is fine. Heat thicker pieces more. This can be time consuming as aluminum tends to conduct heat easily, and the whole part usually needs to get up to temperature. A digital laser thermometer is helpful for determining temperature. I got mine from Harbor Freight for less than $50. You can weld without preheating, but there is a tendancy for cracks to form around the weld from the rapid shrinking that occurs when the weld cools. It is also much harder to start the arc on a cold piece.

3.) Arc starting is hard, much harder than steel. A copper strike plate is helpful, as in TIG welding. This is the area that requires the most practice in my opinion.

4.) Once the arc strikes move! Aluminum welds much, much faster than steel. Be prepared to feed the rod in much quicker. This goes a bit more like soldering a pipe than welding. If you move too slow burn through and melting of the parent piece is the likely result. Your technique needs to be good, so you can do what you need to do, and make a good weld in a very short time period.

5.) Amperage is lower than for steel. I effectively welded a 1/2" thick casting with only 75-80 amps. I used up to 150 amps for the root pass to ensure good penetration and strength, then cleaned the slag from the weld, preheated again, and stiched on top of the root weld with lower amperage. The repaired casting looks like nothing happened once it was ground and shaped.

6.) The only rod suitable for welding aluminum is 4043 rod. You can get these from welding shops, or even at Tractor Supply or Sear Hardware. The slag is white and harder to remove than steel slag. Make sure you get it all before trying to weld on top of a previous weld. The rods I got from Tractor Supply were about $7.50 for 10 rods. I used four or five rods fixing the casting ear.

Post back with any questions or comments. I wanted to start this thread to give people an alternative to TIG or MIG welding aluminum.

 

I haven't stick welded aluminum since the early 90's. MIG is so much easier and I've never TIG welded yet.

 

Once you go TIG for aluminum (or even steel. monel, inconel, or castings) you'll never want to go back. HF starts are the nuts, and heat control with the foot pedal is so much easier.

 

I tried some alum. rod in the arc welder last year. I had a tough time with it. Upon initial arc, it didn't want to penetrate so I would start to the side a bit to build heat. Then as I welded, it built up heat and I had to move very fast to keep from burning though. Overall, not easy without some practice. The weld was strong enough for the application but didn't look all that nice. Arc starting wasn't bad. If you have problems with it, a grind on the arc end usually clears that up. It takes a few seconds, but what is a few seconds when you do 2 hrs of alum. welding each year.

TIG/MIG is a lot easier, but not worth it if you don't need to do alum. that often (like Stephen 87 IROC's case). By the way, you used four or five rods to fix an alum. case ear? That is a lot of rod if it was 1/8". What diamteer rod did you use? The alum. rod coating seems to be very sensitive to moisture. Need to keep it in a dry cool storage unit.

Alum. conducts heat better than steel so you always need more AMPs to weld it. The AMP reduction you saw was due to pre-heating. If you pre-heated steel the same way you would see that the AMPs used to weld it would be less than alum. welding.

Welding alum. with an arc welder is "fun" because it is tough to do. I give you credit for trying it and hope your welds are strong.

EDIT - To Tig weld a "normal" car trans ear, It would take a fair amount of heating to weld it with a <200 AMP, < $2000 TIG welder.

 

Since you can't edit posts 5 minutes or older anymore...........

EDIT - I think Cast is always better with arc & nickel rod. The 500* F pre-heated casting in tough when you have your meat handlers right close to it holding the torch. The deerskin TIG gloves can't take that kind of heat for too long. The big clumsy arc gloves are OK.

 

The casting ear was a bit of a challenge. I didn't have the broken piece to simply weld back onto the case. Instead I had to saw the fractured section off for a clean, tight fit with a new piece. I sourced a thick section of cast aluminum from an old alternator case, cut it to fit, and then welded it to the trans case. I had a factory hole in the alterantor ear that needed to be filled, some gussets from the case to the ear that I re-built with weld for strength. I did a lot of welding, followed by grinding, until the shape was perfect. That's why it took so much rod. If I'd had a simple repair to make I probably could have done it all with one rod. BTW, it was 1/8" rod.

I've noticed that the amperage and effectiveness is also radically different between my AC machine and the DC machine. The DC is a lot more stable and steady than the AC. Less spatter and slag with the DC machine. I think a lot depends on the machine and filler material. My MIG really doesn't get good penetration into anything thicker than 3/16" mild steel, even set of "kill", which for it is 135 amps. I can usually arc weld 3/16 mild with as little as 110 amps and get excellent penetration.

The pre-heating definately makes a difference in terms of amperage required too. Aluminum cools so much quicker too.

I've been arc welding cast iron with a rod from US Forge meant for cast iron. The results have been great, and the rod doesn't have a nickle content that is so high that it is unmachinable after welding. Rod material & flux chemistry have come a long way in the last couple of years. It's making arc welding a lot easier, and allowing arc weldors to fix things that previously were considered nearly impossible. I have no formal training in welding, but have read extensively and weld quite often. With practice I think I've become a rather good weldor. Ultimately that's the biggest secret.

 

Yeah, you did it right. That is why you used more rod. No training here either. Just the good old internet and reading anything I can by someone that sounds like they know something.
I have zero very little A/C arc welding and pretty much stay away from it because it was a pain. I always get DC- or DC+ rod.

I usually use 55%-65% nickel for for the cast iron. I just picked up some Lincoln Ferroweld rod to try for an old wood stove. That rod will rust like steel but the overall properties are not as good as the nickel rod. It is very cheap because it is non-nickel, but I want to use it more for appearance. Nickel is just too shiny for this old thing. I can't wait to try that rod. Too many projects taking up time right.

Yeah, I read a thing before "you gotta burn to learn". Practice is everything. Getting someone to show you the basics in 10 minutes or less is always a huge head start.

 

Were you using DC- or DC+?

What brand rod was it? With rod, just like flux core mig wire it makes a big difference. Basically, it appears that in those 2 cases anything that gives a weld deposition with the correct properties can be called whatever grade. Compare hobart’s and lincoln’s plain old flux core (for the life of me I can’t remember the grade right now), they weld, sound, feel and leave totally different slag but are graded the same.

How about some pics of the weld beads? Any luck with thinner stuff like 1/8" aluminum, or just big castings?

 

DC reverse polarity (electrode positive). You could probably use either polarity, but the information that was printed on the pack of rods said that DC reverse was prefered. My understanding is that the polarity affects how much heat and therefor penetration you achieve. In this case I just follwed the instructions.

The rods are from Hobart I believe. They are packed in a different packaging, but say Hobart right on the rod. The company probably just buys larger quantities of Hobart rod and then breaks them up into packs of 10 for re-sale. Most big welding shops won't sell rods in quantities of less than 5 pounds, and that's a lot of rods for the hobbiest.

I didn't try any thinner stock yet, but purposefully bought some stock to test at a later date. I am confident that it will weld thinner material well too.

I need to know how to post pictures. Can I simply paste a picture into the message box? If someone can tell me I will post some pics of some test beads. With good technique the bead looks good. It isn't the intricate pushed out stack of dimes that a TIG would leave, more like a standard well laid arc bead on steel. If done properly and in a non-critical area (like where it would interfere with something if the bead wasn't ground) I think the bead is pretty enough to stand on its own.

 

I just used so of those rods myself the other week.

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