What Is a Welding Alloy? A Breakdown of Types and Best Practices

welding aluminum alloy

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All you need to weld are two pieces of metal and a heat source, right?

If only this age-old craft were so simple. Among the other materials necessary to fuse strong metal joints, welding alloys are essential pieces of the puzzle.

What Are Welding Alloys?

Also called filler metals, welding alloys are additional metals that fill in the gap between the two base metals being joined.[1]

One definition is “the metal to be added in making a welded, brazed or soldered joint.”[2] The weld joint consists of the base metal and welding alloy.[3]

Filler metals can be unalloyed, or pure.[4] Combinations of metals, known as alloys, are also commonly used.[5][6] Welding alloys may contain nonmetal materials, such as flux, a powered material that produces a shielding gas and protective slag when heated.[7]

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Several welding processes use a consumable electrode, meaning it melts into the weld pool. This means that the welding alloy doubles as the electrode, not only stabilizing the arc but also filling the weld seam.

What Types of Welding Alloys Are There?

Welders have many types of alloys to choose from. They can differ in material, form and properties.

Organizations and manufacturers have multiple identification systems for the various kinds of welding alloys.

Common Welding Alloy Materials

Several ferrous and non-ferrous metals, as well as other materials, can be used as welding alloys:

  • Aluminum
  • Bronze
  • Cast Iron
  • Cobalt
  • Copper
  • Magnesium
  • Nickel
  • Steel
  • Titanium
  • Zirconium

Many different combinations of the above materials exist as welding alloys.

Welding Alloy Forms

Filler materials come in many different shapes and sizes:

  • Composite
  • Paste
  • Powder
  • Solid wire
  • Sheet
  • Foil
  • Thermite mix
  • Tubular wire

Welding Alloy Properties

Welding alloys have varying properties. Some cannot be joined with certain metals and either won’t bond or will produce a weak joint.

Two important characteristics to know are tensile strength and yield strength:

  • Tensile Strength: the breaking point of an alloy.
  • Yield Strength: the point when stress and pressure cause an alloy to deform.[8]

These are just two of the mechanical properties of metals, “the measurable properties that allow a metal to resist external forces without failing.” You’ll learn about others like hardness, brittleness and ductility in your welding classes.

Welding Alloy Identification Systems

Several major organizations have identification systems for welding alloys:

  • American Welding Society (AWS)
  • American Society for Testing and Materials (ASTM)
  • American Iron and Steel Institute (AISI)
  • National Electrical Manufacturers Association (NEMA)

Many manufacturers have their own system, which they’ll include along with the AWS system on the packaging of their products.[9]

How to Use Welding Alloys: Best Practices

Here are three factors to consider when selecting an alloy:

  • The properties of all the materials to be welded
  • The applicable reference specifications and standards
  • The welding process[10]

Material Properties

One mistake beginner welders often make is fusing incompatible metals.

The base metal and welding alloy should have compatible properties. Combinations of metals that form brittle compounds, for example, should be avoided because the finished product could be prone to cracking or breaking.[11] Another factor is how easily the alloy will bond to the base metal.

It’s important to think about how the finished product will be used. Will it have to endure high levels of stress? If so, select stronger alloys, such as combinations of nickel bronze or aluminum bronze.

Similarly, alloys with greater flexibility should be chosen for products that will be bent, and corrosion-resistant allows should be chosen for those that will be exposed to water.[12]

Even more consideration is necessary when welding dissimilar metals. The welder will need to match the properties of the base metals and welding alloys to prevent discontinuities or defects.

Welding Standards and Specifications

Manufacturer, industrial and government standards exist for welding alloys. Below is a list of some of the common industrial standards:

  • ISO Welding Electrodes and Welding Consumable Standards
  • ASME Welding Electrode Specifications
  • DIN Standards for Welding and Surface Treatment
  • ASTM Welding Electrode Specifications
  • AWS Welding Alloy Specifications and Codes[13]

Welding Processes

The type of welding alloy used depends on the process. Recall that some welding alloys come in the form of consumable electrodes.

• Submerged Arc Welding (SAW)

SAW uses a consumable electrode. Powder flux is fed through a hopper to shield the work.

• Shielded Metal Arc Welding (SMAW)

SMAW, or stick welding, employs a flux-covered consumable electrode. The flux melts and forms into a gas to shield the work.

• Gas Metal Arc Welding (GMAW)

Also called MIG welding, this process utilizes a consumable wire electrode. Shielding gases are emitted to protect the work.

• Flux-Cored Arc Welding (FCAW)

As the name suggests, wire fed alloys with a flux core are employed for this semi- and fully automatic process.

• Gas Tungsten Arc Welding (GTAW)

With this process, commonly referred to as TIG welding, the tungsten electrode does not melt and become part of the weld. Instead, the welder hand feeds a rod or wire into the weld pool. Shielding gases prevent atmospheric contaminants from compromising the work.[14]

The Vital Role of Welding Alloys

Welding alloys play an important role in fusing strong metal joints. There are many types of alloys and considerations for using them, but don’t get overwhelmed. As you progress in your welding classes, you’ll learn more about the materials in the middle of weld joints.

Check out what else you could learn in welding school.

Additional Sources

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