The United States is one of the world’s top aluminum-importing countries, consuming 2.87 million metric tons of the common metal in 2020. This versatile and lightweight material is typically used for packaging, construction, and electrical purposes.
However, even experienced welders can have difficulties working with aluminum. Aluminum has higher conductivity and a lower melting point than steel; because of these properties, a thinner sheet can get easily burned during the welding process.
Even if you’re well-versed in steel welding, those skills may not translate to aluminum welding as they rely on different techniques and processes. Keep reading to find out more about these differences and how to successfully weld aluminum.
Why Is Aluminum Such A Popular Material?
Aluminum is the most abundant metallic element. After electrolytic processing made it possible to get pure aluminum, welders began using this versatile metal for all kinds of purposes. Here are the properties which make it such a common metal of choice:
- Lightweight: Steel is stronger and less likely to warp under extreme conditions. However, aluminum has a superior strength-to-weight ratio (SWR) compared to steel. It is the ideal material for projects that need a durable, light material. This lower weight is perfect for reducing vehicle weight and fuel consumption. According to the Department of Energy, reducing vehicle weight by 10% will reduce fuel consumption by 6% to 8%. Because of the higher demand for light and environment-friendly vehicles, aluminum is increasingly being used to make a stronger, more lightweight base for vehicles.
- Non-corrosive: Aluminum oxidizes very easily. While this makes it harder to weld and fabricate aluminum, it also makes it the ideal metal for pieces that will be exposed to corrosive elements.
- Temperature: Aluminum has a lower melting point than steel. However, it also gets stronger and more stable as the temperature drops. This makes it a superior choice to steel in some applications, as steel becomes more brittle at lower temperatures.
- Good conductibility: Aluminum is a good conductor of heat and electricity, comparable to copper. While copper is still the better conductor, aluminum is lighter and very affordable.
Why Is Aluminum Welding So Hard?
Aluminum has many strengths as a material, most especially the fact that it’s non-corrosive and lightweight. However, aluminum is also a soft and very sensitive metal, which is why it can be difficult to work with and weld. Below are more reasons aluminum welding is harder than usual:
- High oxygen affinity: Most aluminum has a layer of aluminum oxide on top of it, created by the metal reacting to air or moisture exposure. This layer protects the rest of the metal from oxidation; however, it is also the reason why aluminum is so hard to work with. Aluminum oxide melts at 3,762 F, which is a higher temperature than aluminum’s melting point of 1,221 F. Melting aluminum oxide requires very high heat, so welders need to be careful not to melt the more heat-sensitive pure aluminum underneath.
- Easy contamination: Aluminum is more prone to impurities than other metals. This can taint the workpiece, causing weakness or defects. To avoid contamination, aluminum needs to be stored in a clean and dry place at room temperature. And even if it is stored properly, aluminum should always be cleaned before welding as a precaution.
- Varying thickness: Aluminum comes in different thicknesses, which impacts how you weld. Welders need to be careful with aluminum workpieces because the high heat needed to melt aluminum oxide will melt pure aluminum in a matter of minutes. But if the thick aluminum oxide layer is not properly penetrated, it can result in a weak weld that can easily break.
- Porousness: The more aluminum heats up and melts, the faster it will absorb hydrogen. Any absorbed hydrogen will then start to separate from the aluminum. This will create bubbles in the workpiece, making it weak and porous.
How To Prepare Aluminum For Welding
Because aluminum is prone to impurities, a welder needs to keep it as clean as possible. Here are some tips for preparing this metal and preventing contamination:
- Clean the workpiece’s surface thoroughly: Remove any condensation, oil, or grease using solvents or mildly alkaline solutions. Strong soap and acetone are common choices for surface cleaning.
- Store aluminum at room temperature in a dry place: Aluminum will absorb any nearby moisture from its surroundings, including the air. Keep it at a stable temperature and away from water.
- Weld aluminum as soon as possible: Aluminum should be welded within a few days. If it isn’t welded within three to four days, clean the joints again.
- Cover the joint before welding: If the joint won’t be welded immediately, it should be covered. This will keep grit and dust from contaminating it.
Kinds Of Aluminum Welding Processes
There are different ways to weld aluminum, and each one has its advantages and disadvantages. Here’s how each process works.
Gas Tungsten Arc Welding (GTAW)
This process is also called TIG or tungsten inert gas welding. It is the most popular method for aluminum welding because it can be used on thinner sheets without burn-through. However, GTAW needs constant current equipment to keep the aluminum from overheating.
In GTAW, a welder feeds the filler to a puddle. This allows the alternating current (AC) to clean the aluminum as it welds, removing the oxidized layer. This also prevents contamination of the aluminum.
Here are some tips for successful GTAW:
- Use the right rod alloy: Pick a welding rod with an alloy as close to the alloy of the piece as possible. Pure tungsten is the usual rod of choice.
- Use a heat sink: A heat sink will absorb excess heat, allowing the welder more control and preventing the material from warping.
- Clean workpieces thoroughly: Carefully clean and preheat aluminum to avoid contamination.
- Control the flow of argan gas: Argan gas is used for shielding during the welding process, but it can arc irregularly if the flow is too strong.
Gas Metal Arc Welding (GMAW)
GMAW is also known as MIG or metal inert gas welding. Like GTAW, this method also needs a welding rod as close to the alloy of the piece as possible.
GMAW can be done through pulse arc welding or spray arc welding methods. For pulse arc welding, the welder will need an inverter power supply. For spray arc welding, the welder requires constant voltage and constant current machines.
Here are some tips for successful GMAW:
- Keep the material and rod clean: Keep the workpieces and filler rod dry to prevent the aluminum from becoming porous.
- Clean workpieces thoroughly: Remove as much oxide as possible. File workpiece edges that will be joined together.
- Use a heat sink: A heat sink will give you more control over the welding and prevent warping.
- Prepare the wire feed: Avoid pulling while welding. GMAW relies on mechanical wire feeding, which can cause issues and result in workpiece defects.
- Push material instead of pulling. By pushing at a 10 to 15-degree angle, the welder ensures that the shielding gas completely protects melted aluminum. This will prevent pinholes and avoid trapping impurities in the weld. With practice, the proper push technique keeps the weld from being weak and porous.
It’s possible to weld aluminum using a gas torch. However, burn-through is most likely when using this process because it’s difficult to control the heat applied to the metal. This method is better suited to more experienced welders who know how to handle a torch and rod.
With resistance welding, a welder passes a current through the workpiece and applies pressure to weld workpieces. This can be done on aluminum, but caution is advised because the lightweight metal has very high electrical conductivity.
Tips For Successful Aluminum Welding
It takes time, patience, and practice to learn how to weld aluminum. However, there are some standard steps that need to be taken, whether the welder is experienced or a beginner.
Here are some crucial tips for how to weld safely and properly:
- Keep the aluminum clean: The purity of the material is key to a proper weld. Contamination weakens the material and can result in poor welds that easily break.
- Wear proper PPE: Welding metal can be dangerous and result in serious injuries. Personal protective equipment, aka PPE, is a must. Wear a welding helmet or safety glasses to protect the eyes, and use gloves and the right shoes to protect the body from metal sparks.
- Use a stringer bead technique: This allows more heat to build up instead of weaving. It will allow the welder to hit the metal with much higher heat and, as a result, there will be better heat penetration and joint fusion.
- Weld in a well-ventilated area: Welding can release a lot of fumes and soot, which can damage respiratory health. Proper ventilation in the welding zone will prevent welders from breathing in toxic welding fumes.
- Double-check work for pinholes: Do not ignore small details or be impatient during the welding process. Small defects can result in poor welding work that can easily be damaged.
Welding aluminum can be a challenge without the right equipment and experience. However, it’s worth it to learn how to weld aluminum because it has so many uses. With proper cleaning and careful heat control, a welder can create a clean, uncontaminated, and strong workpiece.