A Selection Guide of MIG Welding Wires

MIG welding wire is a spooled-up electrode that is fed through a MIG welding “gun” and melted to fuse metal together and join some workpieces. Sounds pretty simple, right?

Well, it is not that simple. There are many different types of MIG welding wire, and in this article, we will explain some of the differences between the types of wire, things to consider when selecting welding wire, and why it’s important to select high quality wire.

MIG Welding Wires

MIG (metal inert gas) wire provides filler metal for GMAW (gas metal arc welding) processes. Also referred to as filler wire, the tungsten solid wire in MIG requires an external shielding gas to exclude contaminants from the weld pool.

MIG wire is essential to MIG welding and is the consumable used in the MIG welding process. The wire is made of metal, generally steel or aluminum or copper metallic coated rod (non-solid wire) and is an essential part of the welding process as it is spooled on either a drum or coil.

The wire is fed through a welding gun which will provide an electrical arc to heat the wire to melt the wire to fuse (bring together) two or more pieces of metal.

Compared to manually moving the welding rod with TIG welding or stick welding, in MIG the solid wire feed is automatically feeding at a given welding speed (the wire is ultimately being melted in the welding process). The solid wire fuses (joined) the two pieces together to form a strong bond.

Furthermore, the semi-automated, automatic feeding process of MIG welding wire has enabled welders to have an increased productivity, hence the reason why MIG welding is one of the most common processes for hobbyists, novice welders, and DIY welders.

With the right wire type and size chosen, you are able to create a strong welding structure without welding defects. The wire absorbs a fair amount of the heat produced during the welding process to avoid welder burns / injuries.

In conjunction with other aspects of the process means that essentially MIG welding wires are essential elements in the welding process.

Is MIG Solid Wire The Same As Flux Cored Wire?

Flux-Core Wire and Solid Wire MIG (Metal Inert Gas) welding filler materials fall into the same family of welding filler materials. Both have very similar properties; both are steel, both conduct electricity, and both are run with a MIG welder. However, they are different weld filler materials in several respects.

Flux-Core wire is a solid metal electrode which has a “flux compound” inside the electrode. As the wire melts and goes into the welding arc, this flux compound becomes a gas that protects the weld from oxygen, and same as flux-core wire, oxygen creates defects in the weld.

The difference for the flux-core wire is that, it does not require shielding gas – however shielding gas may be used with flux-core wire in some instances, for added protection.

For solid wire electrodes (as the name suggests) are solid metal wire in large reels. Solid wire does not have flux – it only has a solid metal wire, so since it is just metal; therefore it is used with a shielding gas. The common shielding gas is 75% argon and 25% carbon dioxide.

The welder delivers a stream of shielding gas from a container with the wire from the welding gun. The shielding gas protects the weld area and wire from oxidation and defects in the weld.

Depending on the application both solid and flux-core MIG welding wire can have different metals in them such as; aluminum, stainless steel, copper, and silver, to name a few.

MIG Welding Wire Types

MIG Wires For Carbon Steel

When using MIG Welding carbon steel or mild steel you will be welding with an ER70s-6″ electrode and typically 100% Carbon Dioxide or a C25 gas which include 25% Carbon Dioxide and 75%.

The only minimum tensile strength that typically changes when welding is the higher grade of carbon steel for example if you were welding high-strength steel your “ER70S-6” would be an “ER90S-6” instead. The strength of the steel would be different.

Carbon Steel ER70S-6 Electrode Designation

The label ER70S-6 represents the following:

• ER: An electrode or filler rod being utilized in either a MIG wire feed or TIG welding.
• 70: At least 70,000 pounds of tensile strength per square inch of weld.
• S: Solid wire.
• 6: The amount of deoxidizing agent and cleansing agent on the electrode. This is a copper coating on the electrode; there are also different types.

MIG Wires For Stainless Steel

Stainless steel MIG welding has a variety of electrodes, because stainless steel is used on different jobs and using different types of grades of stainless steel. In a lot of cases, stainless steel is welded to Carbon steel in the same job.

For example, a stainless-steel brace that is welded to the building is holding the stainless steel piping. These are the different types of stainless-steel electrodes. There are typically the classes of electrodes when welding stainless steel:

• ER308L
• ER309L
• ER316L

1. ER308L and ER308LSi

These stainless electrodes are primarily used for lower grade stainless steels, i.e. 301, 302, 304, 305 and 308. This isn’t the polished appearance most people think of as stainless steel and is generally used in industrial applications and is subject to rust spots from time to time.

The photograph on the left is of 304 stainless steel welded with an ER308L series wire. The wire designation comprises the following:

• ER: An electrode or filler metal used in either a MIG wire feed or TIG welding.
• 308: the grade of the stainless-steel electrode.
• L: Low Carbon; Carbon is the reason you get the rust spots on stainless.
• Si: (optional) Depending on the electrode manufacturer, Sometimes “Si” is added and in this case, it means high silicone content. Basically, it helps the weld wash better into the metal. Kind of like increasing the heat and holding up the sides longer.

2. ER309L and ER309Si

The 309 series has a multi-use designation due to its usage in welding stainless steel to mild or stainless to carbon or low alloy steels. It will weld stainless steel grades 304 – 310 when needed or weld dissimilar metals together when needed.

The disadvantage of using this electrode to weld steel to stainless is that the weld appearance is more rough. It does the job but no matter how high you turn up the machine it feels like it is running cold. No matter what you do the welds seem to look rough compared to welding stainless steel to stainless steel.

The gas used mostly is the same C2 or 2% carbon dioxide and 98% Argon. There are many other options (some better) of gas but the C2 is the most commonly used. Here is the electrode designation:

• ER: An electrode or filler rod used in either a MIG wire feed or TIG welding.
• 309: The grade of the Stainless-Steel Electrode.
• L: Low Carbon.
• Si: (Optional) Sometimes “Si” is added which indicates high silicone content. Basically it helps the weld wash into the metal better. Kind of like turning the heat up and holding the sides longer.

3. ER3016L and ER316LSi

The primary use of the stainless electrodes is in the higher grade stainless steel category specifically used in food industries and marine applications. The base metals that the ER316 will weld are stainless grades 304,305, 308, 310, 312, 314, 316, 317, 321, 347, and 348.

When it comes to gasses, the most common is C2 (2% carbon dioxide and 98% Argon). There are many different mixtures which to choose from, which all depends on what your welding supplier sells. Below are the wire designations for the ER316L and the ER316LSI:

• ER: An electrode or filler rod that can be used in either a MIG wire feed or TIG welding.
• 316: A grade of the Stainless-steel Electrode. This is food grade and true marine grade. But not the best grade of stainless.
• L: Low Carbon. The carbon is what get’s the rust spots on the stainless.
• Si: (Optional) Sometimes “Si” is added and that means high silicone content. Basically it helps the weld wash into the metal better. Kind of like turning up the heat and holding the sides longer.

MIG Wires For Aluminum

MIG welding aluminum electrode selection is pretty straightforward. There are two typical choices and they are:

• ER4043
• ER5350

There are other options but it is uncommon to require any other electrodes. Regarding gas options, it is always 100% Argon gas unless you are welding aluminum thicker than 1/2 of an inch; you may want to try an Argon Helium gas mix.

In most cases 100% Argon is what most shipyards, power plants, and fab shops use regardless if the aluminum is thick or thin. Here are the aluminum electrode designations:

1. ER4043

The ER4043 is the most widely used MIG filler wire. It is able to weld aluminum grades 2014, 3003, 3004, 4043, 5052, 6061, 6062 and 6063. It can also be used to weld cast aluminum grades 43, 214, 355, and 356.

The gas used is always 100% Argon and on rare occasions, a helium/Argon mix may be used on base metals of thicknesses thicker than a ½ of an inch. The classification and designation of the electrodes are:

• ER: an electrode or filler rod used in a MIG wire feed and also used in TIG welding.
• 4: the aluminum series. This electrode is made from 4000 series aluminum.
• 043: this number reflects the amount of silicone put into the electrode; 4000 series of aluminum alloys have silicone added to make that grade.

2. ER5350

It is noted that ER4043 is the most conventionally used MIG filler wire. The wire will weld the aluminum grades 5050, 5052, 5056, 5083, 5086, 5154, 5356, 5454, 5456. In most cases, you will have 100% Argon as the welding gas, but in rare cases, you can use a helium/argon mix on base metals thicker than a ½ of an inch. The electrode’s designation is clearly defined:

• ER– An electrode or filler metal that can either be used in a MIG wire feed or TIG welding.
• 5– The series of the aluminum. This electrode is a 5000 series aluminum.
• 356– This is a number representing the amount of Magnesium put into the electrode. The 5000 series of aluminum alloys have Magnesium added to make this alloy.

Considerations When Choosing MIG Welding Wire

Neither kind is better than the other – the right type depends on your situation and preference – here are some important things to remember when you buy MIG welding wire.

1. Desired Weld Cleanliness

Typically, when using solid MIG welding wires and shielding gases, a cleaner weld with considerably less spatter is created when compared to flux-cored wire.

The presence of spatter does not, in itself, affect the quality of the weld but it does add additional grinding, polishing and finishing surface preparation needed for painting or other coating therefore solid wire is often the preferred method in those practices.

In your decision-making process for MIG wire, your last consideration is the quantity of wire and form. For example, Lincoln Electric sells ER70S-6 in a 44-pound spool and in a 1,000 pound drum.

Of course, the wire feed system on the welding machine will determine what quantity of wire you use. (A small non-industrial MIG machine uses a much smaller spool than is shown in the image, below).

MIG wire can also be purchased in “TIG cut lengths”, which are three-foot pieces of wire used in TIG welding. Also for this purpose, diameter sizes will be specified as normal TIG rod sizes and not in decimal notation such as 1/16 or 3/32.

2. Workpiece Material

Various types of wire are utilized for various materials. ER70S-3 wire is commonplace for mild steel that is clean, free of oil, and free of rust. ER70S-6 wire contains a deoxidizer and is used for mild steel that is contaminated with corrosion and/or mill scale.

3. Environment

When welding in particularly windy or difficult outdoor environments, flux-core wire is typically more suitable than solid MIG welding wire.

While gas used to shield solid MIG welding wire can be blown away while welding in windy conditions, in turn, unless you use a windscreen, the weld will be of lower quality.

Since flux-core wire has gases that release when it is heated, in these windy conditions, the metal is more effectively shielded.

4. Wire Thickness

Once you have determined a wire type for your welding machine, you will need two other pieces of information in order to purchase this consumable.

The first is the wire diameter of the wire which is usually stated in thousands of an inch. The most common wire sizes for welding on sheet metal are 030 and 045.

A 035-inch diameter wire is the standard that is used for most welded joints, however, it may not be sufficient for thicker pieces of material. You may need a multi-pass weld to get a strong joint.

5. Weld Unit Power

This is directly related to wire thickness. Higher voltage and power means higher thickness. If you have a MIG welding unit that is lower powered, you are not going to have good results using thicker wire.

There are lower overall amperage and output, which can lead to poor melting of the work pieces and a poor quality weld. Always refer to the manufacturers instructions to check the maximum recommended wire thickness.

Conclusion

It doesn’t matter what type of MIG wire you decide to buy, but do make sure that you always invest in quality wires.

While it is true that a quality MIG welding wire may cost initially more than a lower-end welding wire, it is also true that quality MIG wire is way more forgiving, can leave you with a better weld even when some conditions are not ideal, and is still only a small fraction of total welding costs.

As you can tell, there are many variables in selecting the correct wire, so it will take time to learn. Its probably a good idea to learn the most common rod classifications first, and absorb the rest of the arsenal over time.

However, as a starter-level welder, you may find that you need to keep consumables stocked or replace empty spools on MIG machines, for become seasoned professionals.

So, that being said, taking the due diligence to properly select and store wire products is important to avoid costly mistakes when you begin the welding operation your working on.

If you want to stay up to date with welding wire standards, the American Welding Society has handbooks you can purchase.

Although some handbooks can be costly, check to see if your school or workplace has the capacity to use a handbook, and you can photocopy any info you want to use for your literature binder.

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