Metals and how to weld them - Aluminum Properties

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What are the Aluminum Properties that actually make a difference in how we weld aluminum??-

Before we get started, a few points I noticed from watching the video on this page.

I did not clean the metal. It was wire brushed at some point and then stuck on a shelf for several months.

I mention this point because up close and personal in the video, you can see some porosity and crap floating around .

I should have wiped it down with acetone and wire brushed it with a new stainless wire brush.

Or maybe hit it with a sanding disc…something.

Sometimes , I am behind schedule and get the camera all set up, my phone is ringing, my wife and daughter are arguing, I am bending over, my back is hurting, I have my arms wrapped around the camera and suddenly it occurs to me that I don’t have the machine set just right, or I didn’t clean the metal enough….sometimes you have to say WTF? And weld.

Ok back to reality.. oops there goes gravity!

What are the aluminum properties that really make a difference in how you approach making a weld on aluminum? I will tell you what I think in order of importance…to me that is.

1. Is the aluminum even weldable?

2. What is the alloy and what filler rod do I use?

3. Do I need to preheat?

4. What about the aluminum properties - Hot shortness and porosity?

These are usually the biggest questions I ask myself when approaching an aluminum welding job.

Lets go over the 4 bullet points I just listed…

1. Is the aluminum even weldable?

Many aluminum alloys are not weldable. At least not by conventional methods.

Take 7075 aluminum for example.

Its main alloying element is zinc. Its heat treatable and very strong. That’s why its used for aircraft structures. But you cant weld it and expect it to hold for anything that matters.

You might weld a dog bowl for Fido out of 7075 aluminum and get by with that… but a ladder, tree stand, motorcycle frame, or anything else that might hurt someone if the welds failed unpredictably would be a horrible idea.

Please Don’t do it.

Several years ago, I heard from a very reliable source that Alcoa and Easton companies would not even sell aluminum tubing to anyone they thought was going to make a tree stand out of it…and that was known material!!

On 7075 and 2024 aluminum ,the welds might just look fine. Its what happens under the surface ..days, weeks, or months later that matters.

Stress corrosion cracking, liquation grain boundary cracks , crater cracks that were welded over, are all possible on aluminum alloys …especially 7075 and 2024.

Make sure you know what you have and make sure its weldable. Common aluminum types that are routinely welded every day are 1100, 3003, 5052, 6061.

3003 and 6061 are very common and both readily weldable.

2. What is the alloy and what filler rod do I use? Like I said before, you need to know what the alloy is before welding, or at least have a pretty good idea. What I mean by that is lets say someone brings a part to you like a motorcycle bracket and there is a broken weld on it. At least you have a good idea that the part is weldable because it was welded when it was manufactured. But what about a ladder that only has rivets and mechanical fasteners? If the part looks like it would have been easier to weld in manufacturing but they used rivets instead, there is probably a good reason why there are no welds.

Welding a ladder will soften the weld area at the very least and that might just make that area kink and buckle under load. Better not to weld it just to be safe....welding can negatively affect the aluminum properties that were designed in.

One of the main properties of aluminum is that heat from welding softens and weakens the immediate area.

Another issue with knowing the alloy is knowing what rod to use. I like to use 4043 whenever possible but 4043 does not always allow and good color match if the weld is going to be anodized. Here is a good download you may not know about…it’s the alcotech filler metal selection chart.

Here's the link for the aluminum filler metal chart.

3. Do I need to preheat?

One of the most important aluminum properties to consider is Aluminum is very conductive. That’s a good property if you are using for a crock pot or for electrical wiring. But it makes welding much more difficult than steel.

Steel does not conduct heat very well and its fairly easy to weld because of that.

Thick aluminum welds dissipate heat away from the arc and weld better with a preheat.

Even a preheat of 200 degrees F makes a big difference on anything thicker than about 1/4” thick.

Using an argon/helium mix helps too for both tig and mig welding.

But be aware that the hotter you get the part, the bigger that area where strength will be lost. Aluminum that is heat treated can completely lose its heat treatment in the weld area and heat affected zone.

4. what about Hot shortness and porosity? Aluminum is hot short. What that means to the welder is that it has a tendency to crack when it reaches a certain temperature range. That is why when you try to tack weld aluminum without using filler metal, it cracks. Tack welds on steel and stainless do not usually crack so easily but aluminum is different. For tig welding, you have to add some filler metal on those tacks. Another area where hot shortness is a problem is when welding from an edge. Sometimes its better to weld to and edge than from an edge in order to prevent this hot short cracking.

Porosity is another issue. Especially when mig welding…but even tig welds can have porosity.

Porosity is gas bubbles. Gas bubbles caused by some crap in the molten metal that was not able to escape during solidification. It can come from all kinds of things. Even humidity. Sometimes its not a problem and most welders wont even know its there unless they are taking a welding test and the weld gets x rayed.

Things to avoid that can cause porosity:

• Oil or oily solvents or wax used for sanding or grinding for a lubricant. ( bees wax really keeps a sanding disc from loading up but can cause porosity)

• Using certain scotch brite pads or roloc discs can leave a residue that causes porosity.

• Dirty metal – give the metal an acetone wipe if it has any crud on it

• Dirty filler rods – sometimes I go months without welding aluminum and my rods are in the open in a rod tube on my welder. Aluminum welding wire can get a heavy layer of corrosion on it if left out in the open …especially in humid areas.

there are plenty more aluminum properties to consider...but I hope I gave you some things to think about with this video page.

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