MIG Welding Aluminum For Beginners: Complete Guide

Those learning to MIG weld aluminum will quickly realize that this type of welding poses many challenges. To be able to successfully MIG weld aluminum, you must use techniques and set-up strategies that will be described in full detail in this guide.

MIG welding aluminum requires techniques and welder settings that will compensate for the material’s susceptibility to many deformities, such as weld cracking. No matter what, aluminum is always MIG welded using DCNP current. There are a variety of other machine settings that must be finely-tuned for the weld to be successful.

Here you will learn how to set-up your MIG welder for aluminum. As part of the process, you will learn how to select the correct filler metal for the specific type of aluminum that you plan on welding. You will also learn how to adjust essential variables, such as voltage and wire feed speed.

What’s Different About MIG Welding Aluminum?

MIG welding aluminum poses different challenges than welding mild steel, due to the physical and chemical properties of aluminum. Workpieces made of aluminum are more susceptible to welding defects that will be discussed in further detail below. Fortunately, these defects can be easily prevented if you use the right techniques and set your equipment up for MIG welding aluminum.

Low Melting Point

Aluminum has a melting point of just 1220 degrees Fahrenheit.  Aluminum workpieces have a protective oxidized layer that melts at 3700 degrees Fahrenheit. The protective oxide must be removed from the workpiece prior to being welded.

Carbon steel has a melting point in the range of 2600 to 2800 degrees Fahrenheit and does not contain a protective oxidized layer with a melting point that is drastically different from that of the base metal. Another challenge to working with Aluminum is the fact that it is simply not as workable as other base metals.

Porosity

Aluminum is also more sensitive to defects and impurities caused by welding. Aluminum absorbs hydrogen at a rapid pace when it is heated into a molten state. The hydrogen separates out from other components as the metal returns to its solid-state. Bubbles are left behind, and the metal can become porous and weak.

I recently wrote an article on this subject, have a look at it: 11 common Welding Defects and How to Prevent Them

Impurities

Aluminum welds are particularly vulnerable to contamination from dirt, debris, and moisture in the environment. The welding of aluminum requires special care to ensure that the weld site does not become contaminated and thereafter weakened. Proper filler material and shielding gas selection are mission-critical to preventing contamination.

Thickness

Burnthrough is a common welding defect in aluminum pieces. This is because aluminum pieces are often thinner than what a welder is used to, especially if they typically work with carbon steel. Auto body repair frequently involves the welding of aluminum pieces that are vulnerable to burnthrough.

Start Out By Cleaning The Aluminum Surface

When you are welding aluminum, your first step should involve cleaning the surface of the aluminum. This will vastly reduce the opportunity for contaminants such as dust and moisture to enter the weld and weaken it. There are several solvents that you can use to help clean the aluminum.

Acetone is always a good choice for cleaning grease, oil and water vapor off of aluminum. Simply wet a cloth or shop towel and scrub the piece down. You may also use a strong soap such as Oil Eater Cleaner/Degreaser. If you happen to use a citrus-based degreaser, be sure to rinse the aluminum before welding.

Brush Off The Oxidized Layer Before Welding

Aluminum melts at 1220 degrees Fahrenheit, but the protective oxidized layer at the surface of the aluminum doesn’t melt until 3700 degrees Fahrenheit. The aluminum cannot be MIG welded without the protective layer being removed first. Fortunately, removing the oxidizing layer is a pretty straightforward procedure.

You can remove the surface oxides off of an aluminum piece by using a stainless steel wire brush.  It is important that you remove contaminants using a degreaser before using the wire brush. Otherwise, you may embed hydrocarbons or other contaminants into the aluminum. The wire brush method is the recommended method for beginners.

An alternative method involves using less scrubbing to remove the oxides. There exist oxide-removal solutions, such as this one. You are strongly encouraged to take extra care when using such chemicals. When used in excess quantities, these chemicals can actually damage the aluminum. For this reason, beginners are encouraged to use the wire brush method to remove surface oxides from aluminum.

Select The Correct MIG Welding Electrode Wire

Take the time to consider which MIG wire works the best for your needs. There is a specific class of MIG wire electrodes that are designed for welding aluminum pieces. These filler metals have been designed to prevent excess porosity and other such defects commonly associated with the welding of aluminum pieces.

Suitable filler metals for MIG welding Aluminum include:

• ER4043
• ER4047
• ER5183
• ER5356

Of these filler metals, the ER4043 and ER5356 are the most widely-available filler metals on the market. Ultimately, the recommended filler metal for your aluminum workpiece will depend upon the specific type of base metal. Matching filler metal and base metal will help prevent the welding defects mentioned earlier in the article. You can find aluminum filler alloy selection charts, such as this one online.

The ER4043 is typically used for auto collision repair because it is softer than the ER5356 filler metal. If you are performing automotive repair, always be sure to double-check the vehicle manufacturer’s manual to see if there is a recommendation for which electrode you use for auto body repair.

You will find that the ER5356 filler metal is generally easier to feed through the MIG welding gun.  The ER5356 has also been reported to be the most commonly used of all aluminum filler metals owing to its strength. It is recommended for use with 5086 aluminum alloy, which is commonly used to make small aluminum boats.

 It is also the recommended filler metal for 3003 aluminum alloy, the most popular aluminum alloy on the market. This aluminum alloy is used to make gutter, downspouts, and many other similar aluminum objects found around your home.

You can reasonably assume that you will be using the ER5356 MIG wire for most aluminum pieces. Still, be sure to always check an aluminum alloy filler metal selection chart to ensure that you are matching the filler metal and the base metal.

Related reading: Different Types of Welding Rods and Their Uses

Shielding Gas Selection Is Essential

The shielding gas is a critical part of a successful aluminum MIG weld. The purpose of the shielding gas is to protect the weld site from contamination from the gases commonly found in the surrounding air, including oxygen, nitrogen, and hydrogen. One of the most common impurities in aluminum pieces is excess porosity, caused by hydrogen bubbles in the weld.

Proper shielding gas selection can vastly lower the potential for such impurities to occur. There are some MIG electrodes that do not require shielding gases. These are called flux-cored MIG wires.  Under some circumstances, these electrodes will still need a shielding gas.

When you are welding reactive base metals like aluminum, you should use either pure argon (abbreviated Ar) or an argon-helium mixture (Ar-He). Carbon Dioxide (CO2) or Oxygen (O2) would not be a quality choice for a shielding gas under these circumstances because these shielding gases would actually oxidize and deteriorate the weld metal in this case.

Pure argon is the preferred shielding gas for welding thin sections of aluminum. Thicker sections of aluminum pieces may need some mixture of argon and helium for thicker sections, where high heat input welds are being deposited. Generally, you will be using a pure argon shielding gas when you are MIG welding aluminum.

Setting Up The Shielding Gas

Setting up the shielding gas is a straightforward process.

• Ensure that your system is set-up with a combination regulator/flow meter for safety purposes. This system acts to reduce pressure from the cylinder while simultaneously regulating the flow of gas towards the welding gun.

Here is an example of what an Argon flow meter should look like. Setting up the system includes all the necessary maintenance check-ups that will be outlined in full detail in your owner’s manual. The recommended flow rate for MIG welding aluminum is 20-30 cubic feet per hour.

Preheat The Work Piece

Another way to help prevent weld deformities is to preheat the workpiece prior to welding it. This is not a necessary step, although it will be of some help in preventing weld cracks from occurring. The preheating temperature should never exceed 230 degrees Fahrenheit.

Enhance the preheating process by placing tack welds at the beginning and end of the weld zone. Preheating is more necessary with thicker workpieces. In other circumstances, you will find that it does not necessarily improve weld performance. If you are just a beginner, you may not find yourself preheating pieces all that often, as long as you are not trying to weld thick, heavy pieces.

However, it is important to know that there are ways that you can make your life easier. There is a chance that your welder will not generate enough heat to weld the thickest pieces of aluminum that come through your shop. If you were to look into preheating aluminum for welding, a good start would be to look into induction heaters.

Related reading: What is Hot Start in Welding? Purpose of a Hot Start in Welding

Induction Heating

Induction heating systems are one of the safest and most reliable tools used to preheat aluminum systems. This is because there is no open flame, and the temperature is more controllable with an induction heater than it is with a torch. Induction heaters consist of a series of heating coils. One of the most useful tools is a portable handheld magnetic induction heater, such as this one.

While this is not a piece of equipment that is essential to being able to MIG weld aluminum, it is certainly a wise investment as it will make your welding shop more versatile. You can find many uses for a magnetic induction heater outside of welding. For instance, you will find that this tool is useful for removing rusted or hard-to-remove fasteners during auto bodywork.

Use A Push-Pull Wire Feeder For Soft Wires

Part of the set-up process should involve you familiarizing yourself with the various wire feeding systems used in MIG welding if you haven’t done so already. Since the filler metal wires used for welding aluminum are soft, you will need to emphasize looking for a wire-feed system that is good at handling softer, less rigid wires such as the ER4043.

Here are the basic types of wire feeders:

• Push type: the wire is pushed from the spool to the welding gun
• Pull type: the wire is pulled from the spool by wire rolls located within the torch handle
• Push-Pull type: this system consists of a pull motor in the welding gun and a push motor in the feeder, together they add extra tension to the wire
• Spool Gun type: this system consists of a small spool of wire that is located on the welding gun

Push-Pull

Push-pull type wire feeders, such as this one, are commonly used for MIG welding aluminum. This is because they make it much easier to handle the soft wire that is used to weld aluminum. This is particularly the case when using the ER4043 electrode since it is even less rigid than the ER5356.

I recently wrote an article on this subject, have a look at it: Do You Pull and Push When Stick Welding

Spool Gun

The spool gun type wire feeders are also frequently used for feeding the soft wires used for welding aluminum.  You can see for yourself how these systems function by taking a peek at the Lotus Technology MSG094 Spool Gun. Keep in mind the fact that this and the other wire feeder referenced above are not universally-compatible. Always check the owner’s manual of your welder to determine which attachments are compatible with your specific system.

Related reading: Do You need a Spool Gun to Weld Aluminum?

Setting Up The Essential Variables in the Welding Process

The essential variables in the welding process are the machine settings that alter the performance of the welding system. Even the slightest of adjustments can have a drastic impact on weld quality. MIG welding aluminum requires the essential variables to be finely-tuned in the ways that are described in further detail down below.

Current

There is only one type of current that is compatible with aluminum during the MIG welding process.

Direct current, reverse polarity (DCNP) is the type of current that is utilized for MIG welding aluminum. The electrode is connected to the positive pole while the work, also known as the “ground,” is negative. If you do not use DCNP, then your weld will become subject to many types of welding deformities.

Among others, these deformities include

• Excess porosity
• Burn-through
• Weld cracking

If you are used to SMAW or stick welding, then you are used to being able to change the current and polarity depending upon the application. If you are MIG welding aluminum, then you really do not have a choice as far as which type of current and polarity will work best for this application.

Wire Type And Size

Wire type selection was discussed in a section above. Wire types must be matched to the base metal. As for wire size, that depends upon three things:

• The suggested mode of metal transfer
• The thickness of the aluminum
• The position at which the weld will be formed.

Start off the process of selecting wire size by looking at the welding parameter chart that should be located on the welding machine itself. This chart will tell you the MIG wire types that the machine and weld gun are compatible with. In general, it is recommended that you select a wire that is 0.030 inches or 0.035 inches in diameter for welding aluminum.

If you search for aluminum MIG wire online, you will find that many of the ER4043 and ER5356 filler metals come in either the 0.030 or 0.035-inch sizes, as is the case with this Hobart ER5356 Aluminum Welding Wire. 

MIG Contact Tip Sizing

The contact tip is the part of the MIG welding gun that is responsible for transferring the current to the wire being fed through the gun. The contact tip needs to be sized properly for the machine to be able to successfully weld aluminum. The inner diameter of the contact tip should be matched to the diameter of the wire.

If you were to use a 0.035-inch diameter MIG wire, then you would want to outfit your weld gun with a 0.035-inch diameter contact tip that is compatible with your MIG welder.

Always check to see that the contact tip is compatible with your welding equipment prior to purchase, as these components are not universally-compatible.

Voltage Settings

Voltage is the source of heat during the MIG welding process. The proper voltage setting depends upon intricate details that will be discussed in further detail below.

That being said, the manufacturer of the welder should have included a chart of recommended wire feed speed and voltage settings. Keep your settings consistent with manufacturer recommendations.

Your MIG welder probably has dial knobs for you to change the voltage and wire feed speed, as is seen in the user manual for this MIG welder. If you adjust the voltage setting to a high voltage, you will notice a long arc length. If you adjust the voltage setting to a low voltage, then you will notice a tight arc length and narrow weld bead.

 The proper voltage setting is dependent upon:

• Aluminum thickness
• Type of joint
• Welding position
• Electrode size
• Type of weld

There is definitely a sweet spot when it comes to voltage settings. If the voltage is too high, there will be excessive spatter. If the voltage is too low, then there will be excessive porosity and a lack of fusion. The best way to find the correct voltage settings is via a set of trials on test pieces of aluminum. By performing a set of trials, you will be able to get a feel for the specific settings that your machine operates best under.

Wire Feed Speed

The guidelines for adjusting the wire feed speed are similar to the guidelines for adjusting the voltage. Getting a feel for what works right starts out adjustments based on manufacturer guidelines.

You should also perform trial runs on test pieces while making incremental changes to the wire feed speed. The wire feed speed is measured in inches per minute and controls the welding amperage in MIG welding.

• A wire feed speed that is too slow will result in an arc that is so long that it might even burn the contact tip in a process that is referred to as “burnback.”
• If a wire feed speed is too fast,  then the weld bead will feature a high crown and lots of spatter with little fusion. It is vital that you pay attention to both voltage and wire feed speed.

Mode of Transfer

The recommended mode of transfer for MIG welding aluminum is spray transfer, which has been compared to the spray of water out of a garden hose. The spray is typically smaller than the diameter of the MIG wire being used. The voltage and wire feed speed should also be set relatively high.

Setting Up The Non-Essential Variables

Your final step for setting up a MIG welder for aluminum involves tweaking the non-essential variables. These are considered non-essential variables because they are altered in the operator’s direction.

There are no factory-preset welding travel speeds, electrode extensions, or electrode angle settings. There are, however, recommendations for how to set-up non-essential variables for MIG Welding aluminum. These non-essential variables will be covered in this section.

Travel Speed And Heat Sink

There is not an official travel speed guideline for MIG welding aluminum, as there are many factors specific to the workpiece that will determine what the ideal travel speed is. However, Universal Technical Institute notes that travel speeds and deposition rates are generally high in MIG welding, regardless of specific application.

One way to bring the travel speed under control is to use a “heat sink,” as is recommended by Universal Technical Institute. A heat sink is a metal piece, often made of copper or brass, that is placed so that it is adjacent to a workpiece on a bench. It can help to reduce the amount of distortion in the aluminum piece. Aluminum sheets are often subject to distortion if the travel speed is too slow, and too much heat is applied to the weld.

Electrode Extension

It is important to control the electrode extension, or “stick-out” when you are MIG welding aluminum. This is because the electrode extension determines how the shielding gas behaves and how deeply the arc digs into the base metal. Electrode extension is normally defined as the distance between the end of the electrode and the contact tip.

You are encouraged to keep the electrode extension or “stick-out” within a range of 1/2″ – ¾” inch when you are MIG welding aluminum. This will help to prevent issues in which the arc is not digging deep enough or is digging

Electrode Angle

The forehand also referred to as “lead angle,” is the electrode angle that is always used for welding aluminum. The position of the welding electrode relative to the workpiece plays a role in determining weld shape and size.  The lead angle is considered a “push technique.”

This is the opposite of the backhand, or “pull,” technique in which the electrode is pointing opposite from the direction of travel. In the forehand technique used for MIG welding aluminum, the electrode will be pointed in the direction of travel.

The recommended electrode angle of travel is 5 to 15 degrees. If the angle falls within this range, it will be much easier to control the molten pool.

Achieve the Best Quality When MIG Welding Aluminum

In order to achieve the best weld quality when MIG welding aluminum, you are encouraged to complete the weld with multiple passes of straight beads.

A straight bead, or stringer bead, is a weld bead that is generally narrow. Stronger beads contrast with weaving beads that are much wider and “weave back and forth” along the length of the weld joint, as the name suggests.

Stringer beads typically allow the operator to weld in all positions in most applications. With a multiple pass bead, you are not trying to complete the weld in one quick pass. Rather, you are taking your time in being able to lay down straight beads.

Related reading: Can MIG Welders weld Aluminum? How to Successful Weld Aluminum

Conclusion

Those who have tried it know that MIG weld aluminum is challenging. By using the techniques and set-up strategies described in full detail in this guide, you should be able to successfully create quality welds and avoid the pitfalls common to this material’s predisposition to weld cracking and other malformations.

From selecting the correct filler metal for the specific type of aluminum you are welding to adjusting the voltage and wire feed speed, your MIG welding technique – and results – will improve.

Frequently Asked Questions

Here are a few common questions people often have about Welding Aluminum:

What type of welder is used for aluminum?

metal inert gas is normally used for welding aluminum. The welder you choose should use impulse welding or spray arc welding methods.

Spray arc welding requires a constant current and constant voltage machine, while pulse welding requires an inverter power supply.

Is Welded Aluminum Strong?

Welded aluminum is generally weaker than the alloy. In general, with heat-treatable aluminum alloys, the material is heated to a value between 325 F and 400 F in the final heat treatment step.

Can Aluminum Be Brazed?

Yes, aluminum alloys can be brazed. You can repair holes, leaks, broken ears, and cracks with aluminum brazing.

How to “Weld” Aluminum for Beginners >> Check out the video below