Can You Mig Weld Rusty Metal [Facts You Need To Know]

To weld rusty metals, it is a dire necessity to create deoxidizers. For this, stick welding is the most ruthless way to weld rusty metals. But the question remains, can you mig weld rusty metals with a mig welder?

The answer is yes you can Mig weld rusty metal but it is not recommended. Doing so will create a weak joint. As you start welding with electrodes, it would embed to the surface because of the rusts over it and will create discontinuities. 

In this guide I will cover the reasons you should not Mig weld rusty metal also will provide the solutions to the issue. So, read till the end, or you will miss something significant.

Can You Mig Weld Rusty Metal?

Mig Welding Rusty Metal
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Welding rusty metals requires proper metal preparation and execution. The success of welding rusty metals depends on the production of enough deoxidizers to destabilize the layers of rust.

Mig welding wire contains silicon and manganese. Upon producing the arc, silicon and manganese will react with the oxygen from iron oxide (rust). Thus it would separate oxygen from the metal. Ideally, stick welder meets all the requirements for conventional welding of rusty metals.

But Mig welding produces a small number of deoxidizers, which is not enough to weld rusted metal. Also mig will waste more electricity and heat input compared to welding clean metals.

So mig welding a rusty metal is not a good idea.

Challenges Of Welding Rusty Metal

Let’s discuss the challenges of welding rusted metal at length.

1. Low Tensile Strength

Welding frees up the oxygen from metal rust (rust is iron oxide). This freeing of oxygen may react with silicon and manganese. So, additional silicon oxide and manganese oxide will be created.

An increment of silicon and manganese from the alloy will impact the structure and, thus, lower the tensile strength.

2. Unstable Arc and Sparks

Rust is basically the impurities of the metal. When the electrode arc comes in contact with rust, flows of sparks are created randomly. So, you have a tough time maintaining a consistent arc in this case.

3. Heat Barrier

Rust prevents the weld metal from mixing with the base metal. As a result, penetration is not adequate resulting in a weak joint. In the welding directory, this situation is called lack of fusion.

In this circumstance, rust acts as a shield and stops the welded metal from melting and fusing with the base metal.

4. Inconsistent Electricity Flow

Rust is not just a heat barrier but an electricity barrier as well. It will prevent the electrons from flowing naturally. So, you won’t have an easy time creating an arc.

How to Prepare Rusty Metal for Mig Welding

So, you have got a green signal to mig welding rusty metal. Now, it’s to make the rusty metal prepared for mig welding. Once you have accomplished this stage, you are halfway there.

1. Calculate the Thickness

It is undoubtedly the most vital step to ensure the success of mig welding. Without having the idea about the thickness of base metal, you will burn through the metal for sure.

Too thin metal requires special attention and a unique electricity mode. Metal burnouts can be significantly reduced with the SCT (Short Circuit Transfer). The good news is, nowadays, maximum Mig machines have SCT mode.

Thick metals have an extended amount of rust coatings on them. So, there is nothing to worry about being burnt out. 

2. Examine the Rust Situation

You need to gauge how much rust you will have to endure.

A rough splash of rust won’t be an issue. But creating a weld pool would be extremely tough on thick rust. The best solution to this situation is to cut  or trim the bad part.

3. Check other Impurities

Rust has alliances in the form of oil, grease, or paint. If there are many of these impurities, you are in a bad position. These can be as adamant as the rust or even worse. SO clean them with clothes and brush them until impurities reduce.

4. Clean the Surface

To remove rust, you have to use the right kind of deoxidizers. Silicon and manganese act like deoxidizers, and you can use them to decontaminate the base metal.

And, as far as oil, grease, or paint concern, use a good quality wire brush. You may have to tussle a bit longer than anticipated.

Things to Consider while Mig Welding Rusty Sheet and Thin Metal

Welding is pretty straightforward. But, successful welding demands caution and you must follow the rule for better welding. So, I have enlisted some factors you should cordially consider before and at the time of welding. 

1. Metal Preparation

The preparation of the rusty metal is most important in a successful welding process. Clean it with soaked rags or brush. Don’t force while brushing, otherwise the dimension of the metal may get changed.

After cleaning, perform welding with proper safety measures. 

2. Filler Metal Selection

Always try to use filler metals that are thinner than sheet metals. Sheet metals are usually 0.03~0.034 inches thicker.

So, it’s better to choose filler metals of 0.023 inches in thickness. Flux core wire would be better for the task.

3. Accurate Torch Angle

There are no hard and fast rules for a fixed torch angle. It depends on the thickness and the type of joint you are making through mig welding.

Try to maintain a torch angle between 5-15 degrees. An improper torch will result in an irregular weld joint.

For mig welding and creating butt joints, hold the gun at a 90-degree work angle. For T-joints, 45-degrees angle is the ideal work angle, whereas, for lap joints, 60-degrees is the ideal one.

4. Proper Weld Style

MiG welding of rusty or thinner metals performs best in SCT (Short Circuit Transfer) model. With SCT, the possibility of a weld-burnout gets eliminated.

You won’t have to tense much. Almost every mig welding comes pre-equipped with SCT mode.

5. Right Proportion of Shielding Gas

SCT mode works at its peak when a balanced mixture of carbon dioxide and argon gas is balanced. This shielded gas ensures the proper appearance of the welded bead.

25% carbon dioxide and 75% argon gas mixture is the ideal mixture for mig welding rusty sheet metals.

Mig Wire For Welding Rusty Material

There are many types of wire for mig welding. The following are best for welding rusty metals.


For mig welding, the solid wire must contain deoxidizing components. ER70S-6 serves this purpose with flying colors. ER70S-R has the highest percentage of a silicon-manganese rate.

Silicon and manganese both act as an oxidizing component. Both will react with the rust and decontaminate it by separating oxygen from iron. Thus, ER70S-R helps to weld rusty metal sheets.


Despite being expensive, ER70S-2 has titanium, zirconium, and aluminum. Each of these chemical components is a very good deoxidizer.

The efficiency of welding rusty metal is superb with ER70S-2.


ER70S-3 is not well suited for rusty metals but suitable for welding thin metals. How?

First, ER70S-3 has few percentages of deoxidizers, and second, this mig wire is very slim. So, in short, ER70S-3 is good for welding thin metals.

What Is The Best Method for Welding Rusty Metal

Stick welding is the best method for welding rusty metal. The welding rod has to be ruthless enough to penetrate through rust to weld through rust. Stick welding creates an aggressive arc to fight against rust.

Additionally, stick welding produces enough deoxidizers to break the pattern of the rust and free up oxygen. This is called flux coating.

Mig welding is also good for welding rusty metal under some conditions. Make the metal prepared, clean it, and apply the filler metal.

Stick welding is an effortless method, though.

Frequently Asked Questions

1. Do you need to remove rust before welding?

Yes, it’s crucial to remove rust before welding. Rust can weaken the metal and compromise the weld’s integrity. Clean surfaces ensure better weld penetration and strength.

2. How do you fill rust holes with a MIG welder?

To fill rust holes, clean the area, cut out the affected metal, and weld in patches with a MIG welder. Proper cleaning and welding techniques ensure a strong repair.

3. What happens if you weld over rust?

Welding over rust can lead to weak and porous welds. The rust interferes with the welding process, reducing the weld’s strength and increasing the likelihood of defects.

4. Can I weld on rust?

Welding on rust is not recommended. It’s essential to remove the rust to ensure a clean and strong weld. Welding on rusted surfaces can result in a compromised weld joint.

5. What is the best MIG wire for dirty metal?

For welding on dirty or rusty metal, using a flux-core MIG wire is recommended. Flux-core wires have a flux coating that helps clean and protect the weld, making them suitable for less-than-ideal conditions.

Last Words

Rusty metals are always tough to work with. And, when it is about welding, especially mig welding, there are a lot of tasks involved.

The tasks may seem tedious but easily doable if you remain on the right track. Choose a good mig wire, assess the rust condition, remove it, and finally make the final charge.

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