Kodi Welch
Market Segment Manager, Miller Electric Mfg. LLC
Do you have experience with welding aluminum but still run into issues with the material due to its specific challenges?
Beyond the basics of aluminum welding for beginners, you may have more advanced questions about welding aluminum in industrial applications. We cover some aluminum welding tips in this Q&A.
Many variables play a role in setting the proper parameters for welding aluminum. These include the welding process, weld position, joint design, wire diameter and base material type and thickness. First, consult any recommended parameters on the electrode manufacturer’s data sheets for the welding process and weld type. Beyond that, a good way to test whether your parameters will provide the results you want is to weld a coupon with those parameters. Then conduct destructive testing to inspect the weld for proper root fusion.
Selecting the right filler metal is a critical part of creating high-quality aluminum welds. No matter which process you’re using to weld aluminum, choosing the wrong materials can be the start of many problems. Two common filler metals for aluminum are 4043 and 5356. A 4043 filler metal is a good choice for welds that will be exposed to long-term elevated temperatures (more than 150 degrees Fahrenheit), that require reduced risk of shrinkage cracking, where aesthetics are important or when you want to minimize the chance of distortion. A 5356 filler metal is a good choice for welds on 5xxx or 6xxx series aluminum where tensile strength is critical, on 5xxx or 6xxx series aluminum when you need anodized color matching, and on welds that require high ductility and toughness, such as those subject to dynamic loading.
Whether it’s for MIG or TIG welding, be sure to consider the volume of filler metal compared to the surface area to be filled with filler metal. There is often a tendency to undersize the welding wire or rod, but that can result in problems. On a larger weld, using a larger diameter rod or wire can work to your advantage. It introduces less oxides into the weld pool, which helps control porosity. Undersizing the wire can also cause problems when the wire feed speed is turned up too high. This causes arc characteristics to break down and result in lack of fusion because the puddle is too cold. On the TIG side, the opposite issue can sometimes be a problem. An undersized TIG rod can overheat the base material because you don’t get the cooling effect of the filler metal coming into the puddle. This can result in burn-through.
It can be difficult to diagnose exactly what is causing porosity in aluminum welds because there are many possible culprits. A good place to start is plate cleanliness and material preparation. Take the time to clean base metals with solvent cleaning or etching, then brush the material with a stainless steel wire brush prior to assembling the weld joint. This removes any impurities and the oxide layer. Be sure to choose a solvent that will completely evaporate before welding. In addition, check for any leaks in the gas delivery system, and check the O-rings on the welding gun. Make sure the base material and filler metal are not wet with condensation, which can happen if they were brought into a warmer shop from colder outside storage, for example.
Aluminum Material Preparation
Previously, it was common to use pure tungsten (green tungsten) when using a transformer-based welding power source. However, a 2% ceriated tungsten (gray tungsten) is a good choice for today’s inverter-based and transformer-based machines. Gray is a good all-purpose tungsten for both AC and DC welding on steel, stainless steel and aluminum. With gray, operators don’t have to guess which tungsten to use for AC or DC welding. The added elements in the 2% ceriated tungsten can help promote the emission of electrons and prevent tungsten erosion better than pure tungsten. Gray tungsten also has a higher melting temperature than green tungsten, so there is less of a balling effect. The technology in a modern inverter-based TIG welder can result in lack of arc starting or poor arc starting characteristics when using green tungsten. Beyond green and gray offerings (which will cover about 90% of industrial welding applications), other options include 2% lanthanated (blue) tungsten and tri-mixed tungsten. These types can offer more precision for very specific applications.
Picking the right machine for aluminum welding applications involves several factors. First, think about the process you’ll be using, whether it’s TIG, MIG or pulsed MIG. The thickness of the base material and your expected duty cycle help determine the size of machine (amperage) you need. Buying an undersized welder for industrial applications can lead to a lot of frustration. Nonstop welding typically requires a higher duty cycle, so you may need to jump up to a larger class of machine to get the necessary output for continuous usage. Also consider the type of operation. In a high-volume manufacturing setting, it’s unlikely that operators will need to make frequent adjustments to settings or parameters, so a simpler power source may suffice.
Features such as independent amperage control, balance control and frequency adjustment can offer ultimate versatility in welding performance. Today’s inverter-based power sources have the ability to pair features that help welders of all skill levels produce quality welds. For example, functions like independent amperage control and wave shaping help reduce the heat input on thin materials and get more penetration with the electrode.
When welding many aluminum alloys, the weld is often not the weakest point. Instead, the heat-affected zone (HAZ) around the weld will be the weakest point. This is an important factor when a weld is ground out and redone or when there are multiple weld passes, which put more heat into the HAZ and surrounding material. As a result, the weld may be very strong but the HAZ could be weak. Be aware of this challenge with some aluminum alloys and take it into account when designing the weld joint and planning heat input.
Anodizing is a process that converts the metal surface into a durable, corrosion-resistant oxide finish. While different operations may weld anodized aluminum differently, one common way is to use what’s called “bump welding.” Using this method, operators don’t mechanically clean the anodized layer off the metal. Instead, they use a very high amperage to TIG weld it, which provides a lot of arc pressure to push the oxides to the side. The operator dips the filler rod and turns the arc off, causing the oxides to flow back over the top of the weld pool. This keeps a consistent material appearance.
Pulsed MIG welding can provide numerous benefits for welding aluminum. Because pulsed MIG maintains a clean droplet transfer through the entire wire feed speed range of the electrode, there are no short-circuit or globular transfer regions. This helps reduce weld defects and post-weld rework. Also, pulsed MIG typically welds at lower average voltages and amperages compared to CV MIG when used at the same electrical stickouts and wire feed speeds. This amperage difference allows pulsed MIG wire speed to be increased beyond that seen in CV MIG — to match the same amperage seen in CV MIG. This results in increased deposition rate and faster travel speeds, thereby lowering overall heat input. Last, some welding power sources capable of pulsed MIG have additional features, such as arc control, to help you fine-tune arc characteristics. This results in easier use for operators and higher-quality welds.
Successfully welding aluminum requires close attention to many details. It’s important to select the right welding process and filler metal for the application and understand how to properly deal with issues like material prep and heat input.
Posted Jan 15, 2024
Explore advanced aluminum welding methods, including in-depth guidance on MIG and TIG welding techniques. Get answers to complex questions and practical tips for industrial applications.
