Beginner Guide to Aluminum

This page is far from a comprehensive tutorial; it's just some tips and some links to more authoritative information. It's intended for people who want to learn to weld aluminum, but have little no experience in welding aluminum, or even in welding in general. This was a description of me a couple of months ago. In my attempts to learn to weld aluminum, I gathered all the information I could find from a lot of different sources – the very simplistic and under-informative manual that came with the welder, lots of reading on the web, basic welding books with very short sections on aluminum, and very advanced books that were written for engineers which had more equations and formulas than practical welding advice. Then using what I had learned, coupled with a lot of trial and error, I eventually figured out how to get two pieces of aluminum to stick together without cracking, warping, shriveling, or breaking. Along the way I made several key discoveries that would have saved me a lot of trial and error time if someone had just told me about them. I thought I’d share the little I do know and maybe it’ll help someone out there learn to weld aluminum faster than they would have otherwise.

    What do you equipment do you need?
    A TIG (GTAW) welder. Most sources say a TIG (Tungsten Inert Gas) welder, also called a GTAW (Gas Tungsten Arc Welder), is the best method of welding aluminum. I’ve heard aluminum can also be welded with a MIG welder or a stick welder or even a with a gas torch. Since I’ve only used the TIG for aluminum, that’s what I’ll be writing about. TIG welders are fairly expensive and it’s hard to justify buying even the lowest quality units unless you are making money with your welding. The more expensive units ($6000) have a bunch of features that make doing high quality welding on aluminum possible. We have a bottom-of-the-line ($2500) Hobart welder that is described as good for the hobbyist or farmer. As tempting as it was to blame the machine while I was making charred bits of twisted metal instead of neatly welded joints, I came to realize that adequate welds can be made, even with a cheapo machine. What do you get when you spend the extra money on a welder? More amperage (meaning the ability to weld thicker metal), water cooling (I don’t know what advantage this provides, but the gas hood glows orange on our air cooled unit when it’s at maximum output, and it’s only 165A), square wave AC (this allow grinding a ceriated tungsten to a point for a more stable arc), frequency adjustment, and adjustment of the ratio of positive to negative current for better cleaning or penetration. Since my machine has none of these features, I can’t offer any advice on how to make use of them.
    Good welding gloves. I have crappy welding gloves and the painful blisters to prove it.
    A good welding helmet. I hear the gold tinted auto darkening helmets are the best. I have a $20 helmet with a tiny window that falls off my head when I flip it down.
    Argon gas. Mixes will not work for aluminum with the exception of an Argon / Helium mix. Don’t take the tank from you MIG welder to use on your TIG welder – it won’t work at all. You will just make a bunch of burnt metal and soot.
    Aluminum welding rod. I got the 4043, which seems to be the most recommended. There is a good chart at http://www.tinmantech.com on which rod to use for which alloys as well as a ton of excellent metalworking and aluminum welding information. At this point I don’t have any idea how to tell one alloy from another, and I'm not doing any mission critical welding, so don't worry about it. The 4043 has been working well for me.
    A dedicated stainless steel brush that you only use for aluminum. Write “aluminum” on it so it doesn’t get used for anything else.
    A metal bench would be nice. I don’t have one. Stopping your weld to put out a fire is a pain in the ass. This happens to me all the time.
    A squirt bottle with water. This is not for cooling the work, it’s for putting out small fires that aren’t big enough to use a fire extinguisher on. Cooling aluminum rapidly may cause it to crack in or near the weld.
    A fire extinguisher might not be a bad idea if you don’t want to get fired for burning down the shop.
    This next one is VERY important: a heavy long sleeve cotton work shirt. TIG welding produces more UV radiation than any other welding process. The first time I used the TIG I was wearing a tee shirt. I used the welder for 10 min if even that. The front of my biceps and a spot at the bottom of my neck were painfully burned with blisters and peeling skin. I just takes a few minutes to do some serious burning.
    11. Clamps or Vise Grips or whatever your going to use to hold your work in place and some blocks or bars of aluminum or copper to use as heat sinks.

Aluminum, Oxidation, Hydrogen and Porosity

Aluminum, Oxidation, Hydrogen and Porosity.
Aluminum has a high maximum solubility for hydrogen atoms in the liquid form and a low solubility at the solidification point.

Hydrogen dissolved in the liquid weld metal will try to rise out of the weld during the aluminum solidification. Some hydrogen gas pores will be trapped and porosity will occur.

Aluminum combines with oxygen to form an aluminum oxide layer. This micro surface layer will form instantaneously if the oxide is removed by machining or grinding. The oxide layer is porous and can easily trap moisture, oil, grease and other materials. The aluminum oxide layer provides excellent corrosion resistance, but must be removed before welding as it prevents fusion due to its much high melting point point than the aluminum alloy .

Arc polarity, plasma molecular action, mechanical cleaning, solvents and chemical etching are all used to attack the oxide layer. When MIG welding if the layer is not removed sufficiently a black soot will appear either side of the weld. To eliminate the soot, first try to lower the arc length (voltage) as this makes the MIG plasma more dense which provides a more concentrated plasma cleaning action.

The majority of aluminum weld porosity results from entrapped hydrogen gas in the weld pool. Hydrogen is highly soluble in molten aluminum. Hydrogen can be derived from many sources.

[a] Hydrogen from base metal contaminates, hydrocarbons, lubricant, oils dirt, grease, moisture, paints and compressed air and contaminates from pneumatic cleaning tools or cleaning brushes.

[b] Hydrogen from lubricant contaminates on the alum weld wire surface.

[c] Hydrogen from moisture, water leaks in water cooled torches. Water from the gas cylinders. Water from the porous, hydrated, alum oxide layer on the base metal surface.

[d] Hydrogen that results from high humidity, condensation on parts and weld wires.

[e] Hydrogen that results from contaminates from grinding wheels.

To minimize hydrogen and weld porosity potential consider, cleaning, degreasing, stainless wire brushes or carbide wheels to remove the oxide surface. Remember you can always find porosity in the alum weld, the real question is how much is acceptable and what inspection and weld process control method will be used to control the porosity.

To reduce aluminum weld porosity potential, slow down the weld solidification rate to allow the hydrogen to exit. Reduce alum weld porosity with the following 11 points.

[1] To remove the alum surface oxide consider a die grinder (>30,000-rpm) rotary, coarse carbide file. An effective cleaning solution is acetone, beware highly flammable..

[2] Increasing weld parameters, with MIG increase the wire feed rate.

[3] Increase weld size.

[4] Avoid weaves.

[5] Slow down weld travel speed.

[6] Use smaller diameter MIG wires.

[7] Evaluate the weld procedure so that weld heat and weld sequence is used as a tool for porosity reduction.

[8] Use lowest possible MIG weld voltage. Low weld voltage results in short arc lengths which create more energy in the arc plasma providing improved arc cleaning action of the surface alum oxides.

[9]Use a higher energy gas mix like 60 helium - 40 argon. The helium requires higher weld voltage. The 60 helium mix is superior to the common 75 helium 25 argon mix, as the the higher argon content helps stabilize the arc and provides superior weld cleaning action.

[10] Don't use MIG wire wipes clipped on the wire.

[11] Don't use anti spatter within 2 inches of the weld. If you know how to set a weld you would not use anti-spatter.