Welding Aluminium -Recently I had the special opportunity to weld Aluminium and I thought I have to share this cool experience through my blog post. Well, welding aluminum is a lot trickier. It’s not your everyday mild steel so there are a few points that you should know before started welding aluminum.
Unless you want to get bamboozled by how tricky it is. It sort of happened to me when I started welding the material. I kind of rushed in with my TIG torch and started to ignite the electric arc while trying to dab my filler metal little by little.
However, in all that trickiness I managed to get better after just learning from my failure through internet articles and YouTube videos, so it is actually not that hard to weld aluminum. Now you should pay attention because I’m going to share some tips on how to deal with aluminum based on my experience.
Welding for Aluminum:
Introduction of Aluminum
Aluminum is one of the most abundant elements on earth right behind oxygen and silicon, making it the most abundant metal on earth. Yes, you heard that right, even the good all’ iron is still behind this silvery-white metal. It is lightweight, malleable, and also pretty resistant to corrosion. It’s only natural that humans started to utilize aluminium fother industrial and mechanical elements.
However, aluminium developed much slower despite all of the aforementioned advantages this metal had. It happens due to the fact that it’s harder to join two pieces of aluminum through welding (a.k.a low weldability) compared to steel.
Therefore aluminium product only came in shape through casting and joined mechanically with each other (mostly through riveting) and along with it being lightweight, it is mostly applied in the aerospace industry. Until recently the technological advancement in welding made it possible to weld aluminium at a reasonable cost. So the use of aluminum starts to spread mainly to mechanical structure and shipbuilding.
Aluminum came in different characteristic and divided into 8 series based on their main alloying element. The purest form is categorized as 1000 series, with aluminum content higher than 99% it is highly resistance toward corrosion making it bio-friendly and found its use in food industry namely made as food can and aluminum foil. Although pure aluminum is highly resistive to corrosion, it has fairly low mechanical properties, therefore, aluminium is being alloyed with many another element.
They are aluminium – copper alloy (2000 series), aluminium – manganese alloy (3000 series), aluminium – silicon alloy (4000 series), aluminium – magnesium alloy (5000 series), aluminium – magnesium-silicon alloy (6000 series), aluminium – zinc alloy (7000 series), and lastly an alloy of aluminium and other elements (8000 series). The alloying element decreased aluminum’s ability to resist corrosion, however, it is a reasonable price to pay to increase the mechanical properties of aluminum alloy.
How to Weld Aluminum
Aluminium’s ability to resist corrosion came from its thin layer of aluminum oxide that occurs through a process called passivation. This thin film layer help protect the surface of aluminum from contact with the environment, therefore, slowing down the chemical reaction that will corrode its surface. The same layer that protected aluminium from corrosion is actually an obstacle in welding aluminium.
The aluminium oxide film melts at a significantly higher temperature (2000o C approx.) than the actual surface of the metal which will melt at 650o C. Welders should be familiar with this before starting to weld aluminum otherwise he might be frustrated for not being able to penetrate this thin layer of aluminium oxide. To deal with this issue, the surface of the aluminium should be cleaned beforehand.
The cleaning can be done mechanically by wire brushing or grinding or done chemically by pouring a special solvent to remove the aluminium oxide on the surface. TIG welding can also give cleaning action effect provided that the polarity and the gas shielding being used is correct. This is why although slower, joining aluminium with TIG welding is highly recommended.
Another problem in welding for aluminium is its reaction to heat. Aluminium has higher electrical resistance compared to steel, therefore it will generate more heat when welded with the same parameter with steel. If you’re not careful, you can have burned through because of aluminium’s low melting temperature.
Aluminium is also conducted heat more than steel, resulting in a wide area of HAZ and higher deformation. So you have to use the lowest welding parameter as possible when welding aluminium to avoid all of that. To prevent deformation you can also use the stopper, but you have to be careful not to give too much constraint as it can break the material.
Welding Aluminium With a MIG and TIG
There are two ways to weld aluminium. The choice is either TIG or MIG, each with their own advantages. While faster, MIG (Metal Inert Gas) welding is not without a setback. Aluminium is a soft metal, a 1.2 mm aluminium wire will probably stick being pressed like a paste by the feeder and tangled like hell before actually reaching the tip of the torch.
Not to mention that MIG does not provide cleaning action like TIG, so you have to clean the welded surface before start welding. The continuous wire feeding and welding also make this process very hot and very prone to burn through. If you think you’re okay with all of those setbacks, then you should weld aluminium with MIG because it’s much faster.
However, I prefer to join two pieces of aluminium using TIG. Somehow the semi-automatic process like MIG does not necessarily help welder when it comes to welding aluminium. As a welder, you would prefer being able to handle most of the variable rather than letting a machine take over and create much more mess. Trust me, in the case of welding aluminium your senses will work much better than a machine. So TIG Welding is all you need.
I will give a specific case of welding a 5000 series of aluminium, the high magnesium alloy. First you have to prepare the equipment such as gas shielding, if you’re new to TIG welding then I would recommend Argon gas because the gas would help you stabilize the arc so the result will be better in term of weld geometry, if you think you can take challenge, helium gas is a viable option because the gas really help with cleaning the surface of the metal from oxide layer. Next, you need tungsten electrode, any kind of tungsten electrode from the cheapest pure tungsten or the expensive thoriated tungsten is okay, it’s your call.
Next you will need a working TIG Welding machine, preferably the one that’s able to produce high-frequency alternating current, moreover when you weld using pure tungsten because it has the lowest melting point compared to the other tungsten, so you’re going to avoid contact with base metal and the high-frequency current really help with that.
Filler metal is optional, it depends on the thickness of the base metal and its joint design, assuming that you’re not welding an aluminium sheet, then you’re going to need a filler metal rod. When it’s ready you have to prepare the base metal surface first by cleaning it from the oxide layer either by grinding or wire brushing, you really have to clean it well as your life depends on it, because it really helps with the final result.
After that, you have to go set your machine, I myself prefer welding aluminium in alternating current, why? Because alternating current provides a balance in term of weld penetration and surface cleaning and still keeping the tip of the electrode cool enough. This can get better if you have a machine that can modify the frequency of the current’s wave, by modifying the current to be dominant in reverse polarity so it will have better penetration but still able to maintain sufficient cleaning action.
Welding in direct current can be hard, in DC- (straight polarity) for example, you won’t be able to have sufficient penetration through the base metal, though the surface cleaning will be great it won’t be a great advantage since you already grind the surface beforehand.
In the other hand DC+ (reverse polarity) significantly increase your penetrating ability, however, this welding method greatly overheat your electrode and if you’re not careful the tip will melt and contaminate your weld pool. So, to summarize you’re going to use high-frequency alternating current, or alternating current will also work just fine. For the amperage and the gas flow, it all depends on your preference and welding environment.
Please note that aluminium gets hotter than steel so maybe you have to tone down a notch with your ampere setting. Another important note is to modify the tip of your electrode. In the case of welding aluminium, you want to distribute the heat on the base metal surface, so a sharpened tip wouldn’t do. Ball tip is the way because the ball surface area will widen the arc thus spreading the heat to the base metal surface.
After the preparation is done, you can start welding. You want to start slow and don’t rush to dab the filler metal until you create a weld pool with your electrode. You can continue welding from that point and stop occasionally every 10 – 15 cm to let the base metal cool down. If you’re not you will have a burn through. Before starting again, don’t forget to grind the surface of the last weld bead that you’re about to continue your weld on.
I wrote this article based on my experience welding aluminium with TIG welding and some sessions of browsing during my bamboozled time of not being able to figure out why my welding technique doesn’t work. Surface cleaning is the key with aluminium, you really need to pay attention to how well you clean the surface, because the end result of your weld depends on it. My recommendation for a new aluminium welder would be to use argon as a shielding gas to help you stabilize the arc.
Alternating current is currently the best choice when it comes to aluminium due to its balanced property of surface cleaning and penetration. For the welding technique, you can watch a ton of YouTube videos on how to dab like a pro. There are so many tutorials on how to weld aluminium and this article is only one of them. Finally, I can tell you that welding aluminum is not that hard and with effort, every welder can master it.