As a welder or a fabricator, situations will undoubtedly arise that require you to join dissimilar metals. That task can be challenging due to a phenomenon called galvanic corrosion. It occurs when two dissimilar metals come in contact with each other while in a conductive or corrosive environment, and in the presence of an electrolyte.
More specifically, the flow of current between the two metals causes the least-corrosive one to corrode even faster, while the least corrosive metal in the pair becomes more corrosive. Since galvanic corrosion causes weakness, it can make the bond of the joined metals fail. Working with dissimilar metals can seem daunting at first, but you’ll feel better equipped to deal with the challenge thanks to these tips.
The Galvanic Series of Metals lists materials according to their likelihood to experience corrosion if joined. Metals that are close to each other in the Series have little or no effect on each other, and the ones at the cationic or noble end are the least likely to corrode relative to other metals they contact.
Determine how likely the dissimilar metals are to corrode if in contact with each other. If the chances of that happening are high, it’s a good idea to take some of the other precautions mentioned below to reduce the possibility of problems.
Most people immediately think of heat as associated with welding. The high temperatures enable the diffusing of atoms and join the pieces. However, cold welding is another option that depends on pressure instead of heat. A thin layer of oxide on the metals usually acts as a barrier that stops pressure from facilitating the welding of the two materials.
However, a preparatory step in cold welding involves cleaning or brushing the metals to remove the oxide layer. After that, mechanical pressure makes the welding process happen, although a user must apply the correct amount. The welding of some metals only occurs at high pressures, while others do not need as much. Soft metals are the best choice for cold welding because at least one material must be ductile.
One of the most common uses of cold welding for dissimilar metals is to join copper and aluminum, two elements that are challenging to weld in other circumstances. Cold welding may not be the right technique for your needs, but it’s worth investigating to see if it’s a feasible solution.
Risk mitigation requires people to learn about which obstacles they might encounter and determine how to minimize possible problems. When trying to avoid corrosion, risk mitigation starts with choosing the right corrosion-resistant metals for the performance environment and then applying coatings as protective measures when applicable.
For example, if welding painted carbon steel and stainless steel together, paint the welded joint to insulate it from electricity. Also, be aware that certain environments speed the rate of which dissimilar metals may corrode. Most notably, it’s best to avoid welding different metals if the finished part will get exposed to prolonged moisture. However, putting dissimilar metals in a well-drained exterior area is much more suitable.
Another option is to place a transition material between the two dissimilar metals you want to weld. One example of when this is a workable solution is if you’re going to weld two metals that are not mutually soluble, such as copper and steel. Nickel is soluble with both of them, and there are two main ways you might rely on it as a transition material.
The first is to apply several layers of nickel alloy to the steel, allowing you to then weld the copper alloy with a nickel filler metal. Alternatively, use a piece of steel between the steel and copper.
The suggestions above are some of the most straightforward ways to avoid corrosion issues when working with dissimilar metals. However, it’s also a good idea to learn about some lesser-used welding methods that could help overcome some of the most frequent challenges faced.
For example, you can use a technique called fiber laser welding for situations involving stainless steel and zinc-coated steel. Attempts to weld those two materials normally result in zinc vaporization that can cause excessive weld porosity, cracking or surface roughness. Fiber laser welding, though, can eliminate those complications.
Researchers have also investigated the potential of electromagnetic welding, particularly when making copper-steel or copper-aluminum tubular metal joints. The process joins the metals together via a high-speed collision whereby a tool coil provides electromagnetic forces.
As these tips suggest, coming up with a plan for working with dissimilar metals can help you steer clear of problems. Taking the time to learn about your options ahead of time can make you feel confident and well-informed when proceeding with a project.
Article by —
Megan Ray Nichols
Freelance Science Writer
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