Aluminum is a highly valued metal thanks to its extreme formability and versatility. However, it does pose certain challenges when welding. That’s why manufacturers and others need to pay close attention when welding aluminum to ensure they avoid defects. There are certain techniques and best practices that you should know about before you start any welding applications that involve aluminum alloys.
Aluminum is a top choice for many manufacturers and designers because of its extreme light weight and excellent strength-to-weight ratio. That’s not to mention its corrosion resistance, aesthetic appearance and recyclability. With the growing number of alloys available on the market, it’s become easier than ever before to find the right aluminum for any given job.
If you are more familiar with steel and thinking of making the switch to aluminum, it’s important to understand that welding aluminum presents several unique challenges. Today we will examine some of these challenges and offer tips on how to avoid defects in your aluminum welding applications.
What are the challenges posed by welding aluminum?
The first factor that must be considered before starting a weld is that different alloys react to welding in different ways. That’s why alloy selection is so important, and we’ll be going over the best alloys for welding in the next section.
The irony is that the same properties that make aluminum such a desirable metal for manufacturing are also what make it so difficult to weld. One drawback is aluminum’s relatively low melting point, especially when compared to steel. At the same time aluminum also has excellent thermal conductivity. If one is not familiar with welding aluminum or taking proper precautions, it can become easy to burn through the metal in the process. This is especially true of aluminum sheet. It’s also important to have the right feeder material; aluminum is softer than other metals, and weld wire can become tangled.
After welding, aluminum will become weaker than the base material. If you’re used to working with metals such as steel, you might assume that a finished aluminum weld will be just as strong. Unfortunately, non-heat treatable aluminum is usually hardened via a process known as cold working. When welded, the metal will be softened to its original state in a process similar to annealing.
It isn’t much better with aluminum that has been heat-treated. As you are welding the metal, it will be heated to a much higher temperature than the original heat treat process and lose mechanical properties.
The good news is that these problems can be avoided with a post-weld heat treatment to improve the finished strength.
Which alloys are the best options for welding?
Aluminum is conveniently divided into separate classes or families that share the same characteristics. The notation for aluminum alloys normally consists of 4 digits, with the first digit used to signify the family it belongs to. It’s possible to determine an alloy’s weldability based on its family. It’s also helpful to know which weld rod or wire is appropriate, so we’ve included that information as well.
The first class is the 1XXX family of alloys, which are the closest to pure aluminum. These alloys are considered easy to weld. 1100 aluminum is commonly used as filler. The 3XXX alloys exhibit medium strength and are considered very formable, making them very conducive to welding. They are welded using 4043 or 5356 as filler rod material. The 4XXX family is also highly weldable, but these alloys are frequently used as weld rod/wire material. The 5XXX family, also easy to weld, are generally combined with 5356, 5183 or 5556 as weld rod.
The other important families, 2XXX, 6XXX and 7XXX all have drawbacks when it comes to welding but there are certain exceptions. The 2XXX alloys are strong and difficult to weld, but the 2219 and 2519 alloys are two exceptions. 2319 or 4043 are recommended fillers. The 6XXX family cracks easily at high temperatures, but with the proper technique it is possible to weld them, usually with 4043 or 5356 as filler material. 7XXX alloys have issues with cracking and corrosion, but three particular alloys, 7003, 7005 and 7039, are weldable with 5356 as filler.
What are some ways to avoid defects in your aluminum weld?
One of the first concerns to watch out for when welding aluminum is cracking. This typically takes two forms, either hot or cold cracking. The former happens because of shrinkage that takes place as the metal solidifies after welding. It can be avoided if you use a proper filler metal that matches the chemistry of the base metal. Another consideration is the joint design, as poor alignment can lead to cracking.
Cold cracking, on the other hand, takes place because hydrogen dissolves in the welded metal in the heat affected zone, normally when temperatures are below 600°F. To avoid this defect, the metal needs to be preheated so that the base material will not allow hydrogen diffusion to cause the cracking.
Another significant issue when welding is known as burn-through. This is a result of overheating the metal, which can lead to burning a hole all the way through it. It is often the result of improperly matching heat and speed during the weld. Using a lower amperage (TIG welding) or using a gun that pulses (MIG welding) are good ways to avoid burn-through.
Finally, porosity happens when gas gets absorbed and trapped in the melted metal. This leads to weak welds that can easily break and are more susceptible to wear. Adequately cleaning the metal beforehand helps avoid this problem.
Your Technical Resources Partner
While aluminum is suitable for welding applications, it is often not as straightforward as working with other metals. That’s why you need to partner with an experienced material supplier. At Clinton Aluminum, our priority is helping our clients succeed at every step of their procurement process. Contact us today to learn more.