How to TIG Weld an Aluminum Lap Joint


If you’re learning how to TIG weld, then you’ll need to know some information about welding aluminum before learning how to weld an aluminum lap joint. Since aluminum requires different types of approaches compared to other metals when welding, you’ll need to become educated about how to handle aluminum while welding.

How do you TIG weld an aluminum lap joint? When learning how to TIG weld an aluminum lap joint, you’ll need to understand some of the difficulties that come with welding aluminum. You’ll need to know what filler metals to use, and how to feed when welding aluminum once you understand that and the core concepts behind welding aluminum, you’ll know how to TIG weld an aluminum lap joint.

Since there isn’t a lot of information available on the Internet today that covers TIG welding aluminum and aluminum lap joints, we created this guide to help you out. Below we’ll discuss why welding aluminum is different, we’ll cover tips for welding aluminum, and how to TIG weld an aluminum lap joint.

The Difficulties with Welding Aluminum

When welding aluminum, you’ll need to use different techniques compared to welding other metals. Aluminum needs different shielding gasses, requires its own specifications, and also uses a different pre-weld and post-weld process than other metals. However, once you understand the inherent differences that come with welding aluminum, you’ll be able to complete all of your aluminum welding projects with ease efficiently.

Welding aluminum is very different compared to welding other metals. There are a few primary areas of difficulty that come with welding aluminum because of aluminum’s various properties. One of the first challenges you’ll encounter when welding aluminum is the use of fillers. Several types of aluminum alloys require filler material to be welded. 

Difficulty #1: Filler Metal

Certain types of aluminum alloy, like 6061, will wind up solidifying and cracking if you don’t use a filler metal while welding. Also, not only is a filler metal required when welding aluminum, but you also need to use the correct types of filler metals depending on the type of aluminum you are welding. If you weld a 6061 aluminum alloy with a 6061 filler metal, your weld won’t work. 

Difficulty #2: Feeding

The use of filler metal when welding aluminum isn’t the only difficulty you’ll come across when welding aluminum. A second challenge that comes with the use of filler metal is feeding the filler metal. If you’re using a mechanical wire feeding process, then you’ll need to consider using specialized drive systems. 

Since aluminum has a reduced column strength when compared to steel, it is also more likely than steel to buckle if you don’t use unique wire drive systems. So, you’ll need to make sure that you are using specialized wire drive systems, for example, like a push-pull gun, when welding aluminum. You’ll mainly need to consider using individual wire drive systems if you use thin aluminum filler metals as well

Difficulty #3: Thermal Conductivity

Another difficulty that comes with welding aluminum is aluminum’s thermal conductivity. Compared to steel, aluminum has a higher thermal conductivity level. So, merely knowing that means the heat you’ll use when welding aluminum disperses more rapidly compared to when you are welding other metals. That means you might not be able to fully penetrate the aluminum into you are really progressed into your weld. When that happens, welders call this issue a “cold start.”

You’ll need to take special precautions to ensure you don’t experience cold starts when welding aluminum. That’s because you won’t get very far into your welding process with a cold start, as you won’t be able to penetrate the metal effectively. You’ll also need to worry about the large craters created by the higher level of increased conductivity when welding aluminum.

Once you reach the end of your weld process with aluminum, you’ll have a lot more heat to deal with than you did at the start of the welding process. Remember, heat disperses into aluminum relatively effectively, but that can make your metal crater. You need to avoid making craters because aluminum cracks easily when this happen. If you make a crater, make sure you fill it, so you don’t have problems once you finish.

Difficulty #4: Pre-Weld and Post-Weld

Another issue that aluminum presents are different approaches when it comes to both the pre-weld and the post-weld process. With aluminum, you’ll get an oxide layer with a melting temperature that’s higher than what the aluminum has itself. So, you want to avoid these un-melted aluminum oxide particles in the weld. You’ll need to perform an oxide removal process, like wire brushing or chemical cleaning, before you start your weld.

Some aluminum alloys, like 6061-T6, are aged artificially. This aging process is done to increase the strength of the metal. However, the heat from welding will decrease any advantages you’d get with the artificial aging process. You’ll wind up with weak spots in the heated area. So, you may need to use post-weld artificial aging with these types of metals instead.

What Welds Are Best for Aluminum? 

Now that you understand some of the inherent difficulties that come with welding aluminum, we’ll move on to discuss the types of welding you can use with aluminum. When welding aluminum, you can use the following types of welding processes:

  • TIG
  • MIG
  • Laser Beam/Electron Beam
  • Resistance

TIG Welding

TIG welding (also called tungsten inert gas welding) is one of the best types of welding you can use on aluminum. One of the reasons why TIG welding is so amazing for aluminum is because this type of welding doesn’t use mechanical wire feeding. So, if you use TIG welding while handling your aluminum projects, you won’t experience issues with feeding.

With TIG welding, the puddle gets its filler material from the welder’s hands, so you’ll also get a lot of control over the welding process. Another benefit of TIG welding is that it is a very clean welding process. So, you also won’t have to worry about the aluminum you are using as a filler from getting contaminated by the air around it.

MIG Welding

Another form of welding sometimes used with aluminum is MIG welding (also known as metal inert gas welding). With MIG welding, you’ll get higher deposition rates, and your filler will also move at a faster pace. However, you do need to use a mechanical wire feeding system with MIG welding, which is an area that can create problems when welding aluminum.

So, if you are planning on using MIG welding with aluminum, you may need to use a push-pull gun or a spool gun so that you can easily feed the aluminum through a wire. You also need to be careful of the type of shielding gas you use when MIG welding aluminum. For example, avoid using 100% CO2, or 75% argon and 25% CO2 shielding gas. Using these types of shielding gasses work well on steel, but aluminum does not perform well with CO2 gas because it is reactive.

Instead, when using MIG welding with aluminum, you’ll want to check the manufacturer’s recommendation about the type of shielding gas you should be using.

Laser Beam Welding and Electron Beam Welding

Both laser beam welding and electron beam welding can handle welding aluminum. You’ll get a high power density with either one of these beam welding processes, so you won’t need to worry about experiencing as many cold starts.

However, beam welding processes still aren’t as optimal as TIG welding is when welding aluminum. For example, if you go with laser welding, then you’ll need to worry about material light reflectivity. Plus, shielding gas optimization becomes essential when using beam welding with aluminum because you’ll need to avoid porosity.  

So, while MIG welding and beam welding are other options for welding aluminum, TIG welding still emerges as the best option, especially for newbies.

Resistance Welding

Another option you’ll have when welding aluminum is resistance welding. While resistance welding can handle welding aluminum, there are challenges associated with using resistance welding. For example, you’ll experience problems with this kind of welding because of the electrical and thermal conductivity that you’ll get with aluminum.

Also, if you use resistance welding on aluminum, you’ll find that the parameter development time might be quite long. Also, you’ll need special tips and welding equipment to avoid the problems associated with this issue.

So, when looking at all of the different types of welding processes, you can use when welding aluminum, the two best options that emerge are TIG welding and MIG welding, with TIG welding being the clear winner. We highly recommend using TIG welding when handling aluminum, especially if you are a newbie, because TIG welding does a great job of combating a lot of the challenges that are inherent when you weld aluminum.

Welding Processes to Avoid When Welding Aluminum

There are a few welding processes you’ll want to avoid when welding aluminum. We’ve listed those types of welding processes below.

  • Flux-cored arc welding
  • Stick welding
  • Submerged arc welding

The main reason why the above welding processes are not recommended for aluminum is that the welds all of these processes create makes a lot of porosity. We already mentioned that you want to avoid porosity when welding aluminum.

Now that you know what welding processes are best to use on aluminum and why we’ll cover some tips for welding aluminum so that you can stay safe and use TIG welding or MIG welding.  

Tips for TIG Welding Aluminum

Both new and experienced welders often feel that aluminum is a complicated metal to weld. However, if you know how to approach welding aluminum, then that assumption isn’t correct. In many ways, welding aluminum resembles a similar process to welding steel. While it does take some practice to get used to welding aluminum, once you get the hang of it, it can be done relatively quickly. 

Staying Safe When Welding Aluminum

First, we have a few safety tips for covering so that you can keep yourself safe when welding aluminum. Whenever you weld aluminum, you want to make sure the area you are using is well-ventilated before you begin your welding project. By ensuring that the domain is well-ventilated, you can avoid taking in any hazardous fumes. You also need to use safety equipment when welding. We’ve listed the safety equipment you’ll need to use when welding below. 

  • Make sure you protect your eyes with a welding mask.
  • You’ll also need gloves and leathers to stay safe from splatters
  • Purchase a good pair of leather shoes or boots for foot protection.
  • Also, consider getting a respirator if you weld for long periods. 

Now that we’ve covered a few safety tips for welding aluminum, we’ll give you advice on MIG welding with aluminum and TIG welding with aluminum. Since we already addressed above why MIG welding and TIG welding are your best options for welding aluminum, we’ll focus on those two approaches below. 

MIG (Gas Metal-Arc) Welding

The MIG welding process first became popular back in the 1940s. The concept behind MIG welding uses a short circuit combined with an inert gas, which helps to melt your metal. 

Pros:

  • MIG welding tends to be very fast.
  • You don’t need a high skill level with MIG welding.

Cons:

  • MIG welding can only apply to thin to medium metals.
  • MIG welding tends not to be as clean of a process as TIG welding.
  • With MIG welding, you’ll get a lot of sparks, fumes, and smoke. 

MIG Welding Tips

To help you better understand the process of MIG welding with aluminum, we’ve listed a few tips to help you out.

  • Before you start your weld, always get your equipment ready first. You’ll need to make sure you have a push-pull wire feed so that you don’t get tangled up.
  • Also, you’ll need to prepare your metal before you start. Make sure you clean the aluminum. You want to take off any oxide and file edges before you join them together. Keep in mind that it is typically easier to weld thicker pieces at first.
  • Make sure you push when you weld and avoid pulling. If you pull, you’ll drag the weld at an angle that will create a dirty weld. You should push at a 10-to 15-degree angle only with aluminum.
  • You’ll also need to understand how to lay a bead, so practice that. Remember, using multiple-pass straight beads provides a better-looking weld, and also creates fewer weld defects.
  • You’ll also need to use a heat sink, like a brass sink, to take in the extra heat. That way, you can weld slower and use methods that are more similar to welding steel.

TIG (Gas Tungsten-Arc) Welding

We mentioned above how TIG welding is an excellent choice for welding aluminum. With TIG welding, you’re using an electrode that’s covered by an inert gas to complete your weld. Below we’ve listed the pros and cons of using TIG welding with aluminum.

Pros:

  • TIG welding is an immaculate process, so you don’t need to worry about a lot of smoke, sparks, or fumes.
  • TIG welding is also a precise welding process, so you’ll get a high-quality weld if you use it. 

Cons:

  • TIG welding is more expensive and takes longer than MIG welding.
  • You need to have some experience to successfully TIG weld. 

TIG Welding Tips

To help you better understand the TIG welding process when welding aluminum, we’ve listed some tips for you below.

  • Pick your electrode for TIG welding. When using aluminum, you should select a pure tungsten rod.
  • You want to get your meals ready first. Make sure you grab a wire brush and scrub the aluminum clean before you start your weld. We also suggest pre-heating the aluminum.
  • With TIG welding, you’ll need to learn how to control the gas. If you have too much argon going into your torch, you’ll wind up with an off-centered arc.
  • You should also consider using a heat sink when performing your TIG weld. A heat sink will keep the aluminum from warping.
  • Also, make sure you are keeping your filler rod as close to the gas cloud as you can. While this is often challenging, you’ll want to practice doing this before you complete an actual welding project.

Now that we’ve covered tips for using MIG and TIG welding when working with aluminum, we’ll cover how to TIG weld an aluminum lap joint below.

TIG Welding Aluminum Lap Joints

Many metals work well with the TIG welding process. However, the metal that is most commonly used when TIG welding is aluminum mostly because TIG welding can combat the inherent challenges associated with aluminum. TIG welding also works well when you are working with metals that are not as thick. 

While you can use other welding processes when completing your aluminum welding project, as we discussed above, the best method is TIG welding. Since aluminum is so popular with automotive parts and processes, TIG welding has become extremely popular among car enthusiasts. TIG welding is also stable and looks great, so many welders that work for professional racing teams enjoy using TIG welding. 

Issues with Aluminum

While TIG welding works well with aluminum, there are still a few things we need to discuss aluminum that you’ll need to know to work well with aluminum. Aluminum, as a pure metal, melts at less than 1200 F and shows no color changes, like other metals do, prior to melting. So, aluminum will never let you know when it’s hot or ready to melt, unlike other metals.

On the surface, you’ll see an oxide, also called a “skin” by welders, form very quickly on the surface. That area has a melting point that’s about three times higher, at 3200 F. To make things even more confusing, aluminum can boil at low temperatures of around 2880 F, compared to where the oxide will melt. Plus, the oxide is more substantial than the aluminum, so when it melts, it’ll sink and get trapped by the aluminum.

So, because of these reasons, you’ll need to remove the oxide area off of your aluminum before you weld. Fortunately, TIG welding is built for this process. You can use the reverse polarity half of the AC arc, which will help you clean the oxide easily from the aluminum before you begin.

Aluminum and Heat

One thing that makes aluminum unique is that it conducts heat well. So, you’ll need to use a lot of heat when you start your welding. Remember, a lot of heat gets lost in the surrounding base material when you start the welding process. Once the welding has gone on for a period, a lot of this heat moves ahead of the arc. It also goes into the pre-heated base metal with a temperature that needs less welding than the cold plate. If you keep going and there is nowhere for the pre-heat to go, the weld can pile up and become troublesome. 

For this reason, many TIG welders feature foot or hand current controls when welding. If your TIG welder does not have this feature, you’ll want to make sure you get it before you start welding aluminum. With these options, you’ll be able to change your current at the same time as you weld. Keep in mind that some types of aluminum have “hot short” issues and can crack if you aren’t paying attention. 

If you use the right type of filler metal while you weld and also use smaller beads, you won’t run into these issues. You may even want to consider backstepping the first inch or so every time you do your aluminum weld before going in the general direction again. 

The Importance of Filler

As you make your metal weld pool, you’ll be using a combination of both parent metals and filler that will help keep the aluminum from cracking or rusting. The wire diameter that you’ll use should work with a current that you can use to easily weld. Also, remember that the current is limited by the power supply you are using, as well as the joints, alloy, and welding position. 

When TIG welding, using a clean, high-quality filler will create the best welds. If you don’t have neat wire, then you’ll wind up with a lot of contamination in your weld pool. Pollution is an issue because it can cause the aluminum weld to crack at a later time. The common contaminants you’ll find are oil or hydrating oil. 

So, cleaning becomes essential, as does use the right types of filler when welding aluminum

Steps for Welding Aluminum Laps

Below we’ve listed some steps for TIG welding aluminum laps.

  • First, set your TIG inverter to about 140 amps, or somewhere between 100 and 120 amps, and control that with your foot pedal.
  • Set the A/C balance on your machine to about 30% cleaning.
  • Set your frequency to 100-120hz
  • Consider adding a bit of helium for about 90% of your aluminum welding. Just a small amount of helium will create a huge difference. You’ll be lightly floating the ball on the helium flowmeter.
  • Also, use a #5 standard alumina cup and include about 10cfh argon while you are lightly floating the ball on the helium.
  • Use a 3/32″ 2.4mm 2% lanthanotid electrode. Make sure you sharpen it.  
  • Also, use a 3/32” 2.4mm 4043 filler rod, or you can opt for 1/16” 1.6mm

Keep Things Clean!

We cannot stress enough the importance of cleaning your aluminum before welding. You’ll want to make sure you prepare your welding pieces well before you start welding so that you’ll get the most high-quality welds every time. Making sure you don’t have any lubricants when you are welding is necessary for creating excellent welds. So, you’ll have to remove oil, hydrocarbons, and loose particles before you start welding.

You also need to ensure that sheared edges are made to be very clean and smooth before you weld. Of course, remember to remove the lubricants as well before you start welding. 

By cleaning the welding surface well, you’ll bring down the porosity in the welds. Keep in mind that hydrogen can create porosity, and oxygen can create dross. If you leave any oil, oxides, greases, etc. on your edges, you’ll wind up with bad welds. So, always make sure you clean before you weld

Final Thoughts

 Now that we’ve covered a lot of information regarding welding with aluminum, you should have the knowledge you need to TIG weld an aluminum lap joint. We discussed why welding aluminum is different than welding steel, some tips for welding aluminum, and how to TIG weld an aluminum lap joint. With this information, we feel you should have all the information you’ll need to successfully TIG weld with aluminum. 

Learning how to weld can be a gratifying process. Once you start creating and finishing welding projects, you’ll love the intrinsic rewards that will come with creating beautiful welds. While learning how to TIG weld can take some time and a bit of effort, once you get going, you’ll never want to stop. 

Alexander Berk

A bit about myself: I am a certified international welding engineer (IWE) who worked in different welding projects for TIG, MIG, MAG, and Resistance Spot welding. Most recently as a Process Engineer for Laser and TIG welding processes. To address some of the questions I frequently got asked or was wondering myself during my job, I started this blog. It has become a bit of a pet project, as I want to learn more about the details about welding. I sincerely hope it will help you to improve your welding results as much as it did improve mine.

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