When it comes to welding aluminum, many people find it’s not as hard to do as it may seem. Compared to steel or other materials, welding aluminum can be more involved and there are common mistakes you need to be aware of. If you take precautions and educate yourself thoroughly it can be accomplished without incident. This is even true of anodized aluminum if you plan appropriately.
This is good news. Aluminum has many attractive properties, its ability to be anodized being among them. Combine that with the versatility offered by welding, and aluminum gives manufacturers and designers a world of options to ensure their application is as efficient, cost-effective and durable as possible. If you are new to the world of welding anodized aluminum, please read the following before you get started.
What is anodizing and how does it affect aluminum?
The anodizing of aluminum has been popular for nearly one hundred years, having first been commercialized in the 1920’s. Anodizing refers to the process of electrolytic passivation, a chemical reaction in which an oxide layer develops on the surface of the material. During the treatment, the workpiece being anodized forms the anode electrode of an electrolytic cell. The new layer that is formed provides the added corrosion and wear resistance, also allowing for better adhesion from paint primers and glues. While aluminum is the most common metal to undergo this process, others such as titanium and zinc can also be anodized.
When anodizing the aluminum, a direct electric current is applied through an electrolytic solution. This current will cause the release of hydrogen at the cathode, while at the same time oxygen is let off from the anode. This process therefore leads to a build-up of aluminum oxide on the metal’s surface. The voltage generally needs to be between 15 to 21 V, and the higher the voltage, the thicker the coating. Other important considerations include the solution’s electrolyte concentration, its acidity, and its temperature, in order to ensure the consistency of the finished layer.
After the process is finished, the aluminum’s surface will be harder than the base metal. This provides an increased resistance to corrosion, as well as other advantages such as improved lubricity. It will also be easier to dye. There are certain drawbacks. Without a sealing substance being added, the aluminum will be susceptible to wear. After anodizing the surface will be non-conductive and vulnerable to thermal stress.
One reason why aluminum needs to be anodized is because of the alloying materials. In its natural state, aluminum forms a protective layer of aluminum oxide when it encounters oxygen. In pure aluminum, this layer may be from 2 to 3 nm thick. After alloying, passivation may lead to a thicker layer, but it will also be more porous because of the added elements. While the addition of elements such as copper and silicon will boost aluminum’s strength, in many cases it will lower the corrosion resistance. Among the alloys most often in need of anodizing are those in the 2xxx, 4xxx and 6xxx series.
What is the process of welding anodized aluminum?
So why is welding anodized aluminum such a challenge? As anyone familiar with welding knows, the welding process require electrical conductivity in the metal being welded. After anodizing, the aluminum will become non-conductive.
There are a couple of work-arounds available that will allow you to avoid welding the anodized aluminum. First, you can do the welding prior to anodizing. Then the finished weld can be anodized as one piece. Depending on your workflow, this may not be possible. If the aluminum parts you need to weld have already been anodized, this won’t be an option.
Another alternative is to use a sanding or grinding disc and grind away the anodized layer in the welding area. The more accurately you can grind the area the better the result for the cosmetics of the finished piece. Even with careful processing, you may still find that the result is not aesthetically appealing.
When neither of the above options is suitable, it is possible to weld the aluminum after anodizing. It’s important to note that this process can be quite difficult to execute if you are inexperienced. Use the power supply at its maximum current output while welding and energize the arc just long enough to form a puddle. Immediately add a bead of filler and shut off the power. Move over approximately half the weld puddle diameter and repeat. This works best with a welder that has a foot pedal that works the on/off switch, or a finger control switch.
This technique is referred to as bumping. Properly prepare materials prior to starting. Carefully clean all the metal parts to make sure there is no dirt or other contaminants. The metal should also be at room temperature for at least an hour prior to welding, and it’s necessary to ensure there is no condensation or moisture.
Your Trusted Services Provider
If you’re new to this kind of welding, why not consult with an expert before attempting it for the first time? At Clinton Aluminum, our team of sales professionals has extensive experience working with manufacturers and designers, and we pride ourselves on our commitment to ensuring our customers get the right material for the job. We regularly enlist our supplier network for their technical expertise in a variety of processes, including welding.
The ability to weld anodized metal can help your business add value to your market. Make sure you know how to do it right. Contact us today to speak with one of our friendly customer service representatives and learn more about what aluminum alloy is right for you.