Why Is Aluminum Difficult to weld?

Almost every welder gets frustrated at aluminum being difficult to weld. They openly express their bad experience working with aluminum on forums and other platforms.

The story may not be any different for you. You might be almost giving up on using aluminum and you’re wondering why it’s just so hard to weld.

Aluminum is difficult to weld because it is insulated by a tough aluminum oxide layer that requires high heat to break it to reach the underlying aluminum. It also has a low melting point and high sensitivity to impurities which affect its weldability.

Keep reading to discover more details on why aluminum is a hard metal to weld, and the tools and techniques you can utilize to weld it easily.

How hard is it to weld aluminum? 

Aluminum will be hard to weld for you if you don’t know how to go about it.

Just looking at the key properties of aluminum, it presents itself as the perfect metal for welding. It has favorable aspects like being corrosion-resistant, lightweight, good heat and electricity conductor, and it is eye-pleasing.

How hard is it to weld aluminum

Yet, this material is still difficult to weld. You wonder why? Surprisingly, the same traits that make it a good metal for your welding projects are also the same reasons why you find it hard to weld.

Here’s what makes aluminum hard to weld:

1. The insulating layer of aluminum oxide

One of the top properties that make aluminum a good metal for various projects is that it’s naturally corrosion resistant. But how does it achieve that?

Well, it comes coated with a darn thick layer of aluminum oxide. This layer is created as a result of the metal interacting with air and water. Aluminum oxide is an extremely stable substance and puts an end to further corrosion or oxidation of aluminum.

Now, the main problem with this layer is that has almost triple the melting point of aluminum (i.e. aluminum oxide melting point is 3,762 F and aluminum melting point is 1221 F).

For this reason, aluminum oxide acts as an excellent insulator to aluminum, and making direct heat application becomes challenging.

For you to melt through the aluminum oxide and reach the underlying aluminum, you’ll need to apply high heat. The ugly truth about applying high heat on this layer is that it ends burning holes in the aluminum lying underneath due to its lower melting point.

weld aluminum

Anodized aluminum is an extreme case of how difficult aluminum can be to weld. Anodization is a process through which a highly controlled, manufactured oxidation is applied to the aluminum metal. The process creates a thicker and more porous layer than aluminum oxide.

Though it presents more benefits like being more corrosion-resistant, providing an ideal surface for paints or sealants, etc., welding anodized aluminum is darn hard! You might just want to avoid it to save yourself time and frustration.

2. Increased porousness in molten state

Welding involves the production of a lot of heat at high temperatures. As you weld aluminum and it continues heating up, it gets into molten state.

This presents another big problem for welders because aluminum tends to absorb hydrogen at high rates in the liquid state.

After you’re done welding and the aluminum creeps back to its solid state, the hydrogen it took in begins separating out, resulting in the formation of air bubbles inside the material.

weld aluminum molten state

As you can easily guess, these bubbles (or is it pinholes?) will make the metal become more porous and lead to weaker weld joints.

3. High susceptibility to impurities

Aluminum is a highly sensitive material and is even more susceptible to various impurities compared to other metals. This means it’s easily compromised and this can cause problems when you use it in welding.

Air reaching the welding as a result of poor shielding or excessively longer arches can easily taint aluminum. Oxygen also reduces the metal strength and ductility and causes the formation of oxide on your welds.

Hydrogen available in moisture in the electrode fluxes, damp weld joints, humid air, etc., is another way that aluminum gets contaminated.

Luckily, you can avoid contaminating aluminum metal for welding by cleaning it thoroughly to eliminate the oxidized layer and impurities before using it.

If you don’t intend to use the metal right away, be sure to store it correctly to keep air, water, and dirt from contaminating it. Store it at room temperature to oxidization that may occur when it reacts to condensation.

4. Thickness factor

Aluminum is available in varying thicknesses. But due to a low melting point and inability to give you visual cues (more on this topic coming up later), it can be challenging for you to work with.

Remember, you need a lot of heat to break down the aluminum oxide layer to create fusion. And if you’re dealing with thinner material, you can easily ruin it in seconds!

You might also think you have created a good weld into thicker materials when you didn’t even penetrate it deep enough for proper fusing. This can result in a weaker weld that’s highly likely to break.

Thickness factor

Experience will be your best weapon when dealing with aluminum materials of varying thickness.

The more you continue welding it, the easier it becomes to learn how it behaves. This way, you’ll be in a better place to do the welding right for different thicknesses of aluminum.

How to weld aluminum?

Yes, aluminum is difficult to weld and we have explained the reasons behind it above. But that doesn’t mean you should give up on it.

You can still weld aluminum if you know how to go about it! You just need to follow the best practices for welding aluminum and getting quality welds will become easier for you. You also need to get the best welding table with other necessary welding accessories.

How to weld aluminum

Below, we have listed the proven practices and techniques for welding aluminum that you should start implementing today.

1. Pre-welding practices

BEFORE you weld a piece of aluminum, you need to clean it thoroughly to remove any contaminants present on its surface and break the insulating aluminum oxide layer.

These pre-welding preparations help remove the impurities on aluminum and make the metal easier to weld.

As we said above, aluminum is a highly sensitive metal and can get easily attacked by impurities.

Pre-welding practices

Follow these tips to clean your aluminum metal correctly:

  • Start by degreasing the aluminum surface. A mild alkaline like strong soap can work well for removing grease as well as water vapor from the metal surface. You can also use a solvent like acetone to degrease the metal.
  • Use a new stainless steel wire brush to scrub the oxide layer off the metal surface. In case you can’t find an aluminum wire brush, use strong acid or alkaline. But make sure you rinse your metal and completely dry it afterward.
  • Assemble the joint on your welding table and use clean welding clamps to hold the parts in place. If you don’t intend to weld it right away, make sure you cover it to prevent further contamination from dirt and grit.
  • If you want to store your aluminum pieces for longer, make sure they’re completely dry and store them at room temperature. Don’t store them for more than a few days or you’ll have to clean them all over again for welding.

2. Gather the right tools

The best welding method to use for aluminum is TIG or MIG welders. We’ll get into more details about how to use these welders later.

Use filler metals that match your base alloy. The right file metal will give you the right properties for your workpiece and prevent cracking. You can choose the filler metal from 4 main families of aluminum alloys namely 1XXX (99% or more aluminum), 2XXX (copper alloys), 4XXX (silicon alloys), and 5XXX (magnesium alloys).

You’ll also need to choose the perfect grinding disc for aluminum. Since aluminum is a softer metal, you should go with a disc made for soft metals for the perfect finish results.

right tools

Using the wrong disc can make aluminum melt—running your workspace and gumming up the disk itself and running your grinder.

Never use grinding discs used for steel on aluminum. These can not only melt your aluminum workpiece but will also contaminate it. Consequently, never share a disc you use for aluminum on other metals.

3. During welding

When you finally get down to welding your aluminum workpiece and you have your welding machine ready to go, you should use these welding techniques for the best quality aluminum welds.

  • Use the Push technique to weld aluminum: The drag or pull method is not going to give you good results. It is associated with insufficient gas coverage which can create problems given that aluminum is highly susceptible to impurities. Pull technique can result in porous and weak welds. Not to forget it leaves behind an ugly sooty weld. Pushing the gun tip to ensure sufficient shield gas to completely shield your work ice from impurities.
  • Stringer bead technique: Alongside the push technique, you should also apply the stringer bead as opposed to the weaver method. It produces greater heat buildup which is needed for better welds on aluminum. And one of the key properties of aluminum is good heat conductivity. This means you should hit it with high heat to ensure excellent penetration and quality fusion.

Do you need a special welder to weld aluminum? 

You don’t need to use any special welder to weld aluminum. You can rely on popular welding methods like MIG and TIG welding to weld your aluminum projects. Other welding methods like resistance welding and laser/electron beam welding can also work.

special welder to weld aluminum

However, you should NOT use any welders that use flux, including stick welding, submerged arc welding, and flux core welding, to weld aluminum because they can cause porosity of the material and cause joint strength issues.

This is how you use the two most popular welders for the best aluminum welding results:

1. MIG welding for aluminum

This is probably the most popular welding method for aluminum. For starters, MIG stands for metal inert gas. It involves faster travel of heat and higher rates of deposition compared to TIG welding, thus affecting the welding quality.

It utilizes a mechanical wire feeding system which means you’ll need to use a spool gun or push-pull gun for easy wire feeding.

MIG welding for aluminum

When using this method, we advise you to start off by cleaning both your filler rod and the base metal to minimize contamination of aluminum which can end up making your welds porous and weak. They must also be moisture-free to reduce the absorption of hydrogen by aluminum in the molten state.

Above all, you’ll need to have excellent shielding gas coverage for quality welds. Pure argon content works great!

2. TIG welding

TIG (tungsten internet gas) is also a popular method for welding aluminum. it is mostly preferred by automotive enthusiasts and welders working on professional racing teams.

Unlike MIG, this welding method uses constant current equipment that’s AC compatible and uses 100% argon as the shielding gas. No mechanical wire feeding is required here, so you won’t be worrying about feedability problems.

Instead of the wire, this welding method feeds the filler material into a pool/puddle.

TIG welding

The big advantage of TIG welding aluminum is that it’s quite clean—the AC current cleans the oxide layer off the aluminum as it welds it. Moreover, it keeps your aluminum workpiece from getting contaminated throughout the welding process.

Nonetheless, you should still make a point of cleaning your aluminum before you weld it using the method to increase your chances of getting quality welds.

Does welding aluminum weaken it?

Welding aluminum incorrectly can weaken it. But if you follow the correct welding process and use the right technique, you should end up with strong joints and overall quality aluminum welds.

We have already discussed that aluminum easily attracts hydrogen in molten state which later on separates out when the metal solidifies and forms bubbles inside the welds. This can create a weakened weld which makes most people believe that aluminum weakens when welded. However, you can avoid this by properly cleaning and drying the aluminum before welding it.

Does welding aluminum weaken it

If you heat-treat aluminum (for the heat-treatable alloys) before welding, then using the wrong welding method can affect its strength. The welding heat will destroy the prior heat treatment all over the metal from the welding joint (aluminum is a good conductor of heat). And it can be hard for the aluminum to regain its hardness. The best way to avoid this? Consider heat treating aluminum after welding it.

As for making your welds strong and durable, you should make sure you use the right filler material grade. The right filler material should be able to put up with the aluminum tendency to crack at the weld when it eventually cools down (known as hot cracking). We already discussed choose the right filler material based on your base metal alloy.

Is aluminum more difficult to weld than steel?

Steel is much easier to weld than aluminum. It doesn’t involve blasting any insulating outer layer to get to steel, unlike in aluminum. Steel also has a high melting point of 2500 F compared to 1221 F in aluminum. This makes it capable of withstanding the high heat produced during welding without melting down.

You can take your time when welding steel, but you wouldn’t enjoy the same luxury of time when working on aluminum.

When welding aluminum, you need to move 3x faster than you do with steel. The material excels in conductivity and heats up pretty fast as you continue blasting it with heat. The faster your gun tip moves, the less heat you transfer to it.

Is aluminum more difficult to weld than steel

Another advantage of welding steel over aluminum is that it gives you visual cues that guide you through the welding process. As you continue welding it, it will change color, glow, and then change to the molten state. These stages are highly visual and will give you indications on when to add materials or when to move on.

Welding aluminum is a completely different story. The metal only gets shinier as you continue welding it and it can become hard to know the stage you’re at when welding it. But observing aluminum helps you master its behavior and easily pick up the cues and know what to do next.

Final verdict

Aluminum is difficult to weld mainly due to the insulating layer of aluminum oxide, but that doesn’t mean that you can’t weld it. You just need to understand the metal and know the right welding practices and techniques to use when working with it to allow you to work with it easily.

You might not have a good time welding aluminum at the beginning. But don’t give easily up because you’ll be learning and building experience all along. Eventually, you’ll become a pro at it and you’ll be making great aluminum welds.

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