Anyone who has worked with aluminum understands there are several challenges when it comes to welding. Compared to other metals such as steel, aluminum can be somewhat difficult to weld properly; without experience, the result may be an inferior finished product. That’s why it’s essential that you take the time to properly clean and prepare your aluminum work piece before you start welding.
Aluminum offers many benefits: it’s very easy to work with, extremely formable, can take on many different shapes and has a high strength-to-weight ratio. With the wealth of different alloys currently available, including high-end specialty alloys that continue to be developed, there’s a tremendous diversity in what manufacturers can accomplish with aluminum.
What challenges are posed when welding aluminum?
One of the challenges of successfully welding aluminum is that it needs to be cleaned first. Dirt or other impurities can adversely affect the weld, so cleaning is an integral step in the process, but by no means the only consideration.
The truth is that the very qualities that make aluminum so easy to work with are also the reasons it is difficult to weld. Aluminum, in contrast to other metals, has a low melting point; especially when compared to steel. Combine this factor with aluminum’s thermal conductivity properties, and this makes it easy for an inexperienced welder to burn through the work piece. The softness of aluminum also means that the feeder wire may become tangled in the feeder during the weld if you aren’t careful.
Another key drawback is that after welding, the weld-affected area is likely to be weaker than the original metal. People who are more accustomed to welding steel or similar metals will often assume that a finished aluminum weld will be just as strong. This is generally not the case, because when an aluminum alloy is non-heat treatable it will probably have been hardened via cold working. That means after welding it will become softened to its original state, similar to what happens during annealing.
On the other hand, when working with aluminum that has been heat-treated, you have another set of problems. While welding, the metal will be heated to a much higher temperature than during the original heat treatment process. This means that the aluminum will lose any mechanical properties that had been gained by heat treatment.
Ultimately, these challenges are not impossible to overcome. It just takes proper welding technique and making sure you have the right material for the job you are doing. Some alloys will be impractical to weld, while others won’t be that difficult if you know what you’re doing.
How to clean your aluminum prior to welding
Once you have a working knowledge of the basic concepts of welding aluminum, it’s time to get started; that begins with properly cleaning the metal. There are two main steps to cleaning aluminum for welding, grease removal and oxide removal.
First, it’s imperative that you make sure there’s no grease or oil on the metal to be welded. This is because any impurities in the aluminum can impact the weld and lead to defects. Although a metal surface can look clean to the naked eye, there very easily could be oil, grease or other liquids that a simple wiping won’t get rid of. A lot of people will take a rag or brush to wipe off the metal, but this won’t effectively remove grease; it may only move it around and make the situation worse.
In order to be confident you’ve removed all the grease and oil, you’re going to need to use a liquid degreaser. These fall into two main categories, organic solvents and mild alkaline solutions. Examples that work well include acetone, methyl ethyl ketone, lacquer thinner and toluene. Certain liquids need to be avoided, including alcohol, which does not work well as a degreaser, and vapor degreasers, which emit volatile compounds.
Use a lint-free rag to apply your chosen solvent to the aluminum surface and allow the liquid to evaporate before fitting any parts together. Likewise, don’t pour solvent into a weld joint you have already fit together. With certain alkaline solutions, you might need to immerse the parts to be welded into the liquid entirely. If this is the case, it’s important to allow the metal to dry completely before beginning the weld.
After the grease and oil has been removed, it’s time to focus on any oxides. In order to remove oxides, you must physically strip the material from the aluminum’s surface. This can be as easy as using a wire brush, but you need to make sure the brush is clean (an oily brush is going to defeat the purpose) and its good practice to use brushes that are only used on aluminum. Also, using a brush with soft bristles is preferable to a heavy one, which will likely burnish any oxide rather than removing it.
Another option is chemical removal. A good choice for this method is a strong alkaline solution. You’ll likely want to immerse the work pieces fully in the solution. It’s also possible to apply oxide-removal solutions using a spray bottle. Because these solutions are normally phosphoric acid-based, or may contain hydrofluoric acid, it’s important to be extremely careful while using them.
Whatever option you use, once you have cleaned the metal, you’ll have to wait long enough to ensure that it has completely dried. Don’t want to wait too long, because even a few hours are enough for airborne grease and impurities to settle onto your work piece. If more than a day or two has passed, you’ll need to start the cleaning process over again.
If you have any questions, Clinton Aluminum is happy to assist you at every step of your procurement process. To get help with material selection and more, please contact us today.