What Metals Can Be Friction Stir Welded?

As modern manufacturing continues to evolve, so too does the technology behind how metals are joined. One of the most transformative innovations in this field is friction stir welding (FSW)—a solid-state process that allows materials to be joined without melting. Unlike traditional welding, which uses high temperatures to fuse metal together, friction stir welding relies on mechanical stirring and frictional heat to soften materials and form robust, high-quality bonds.

This process has revolutionized metal joining in various industries, from aerospace to automotive, marine to electronics. But not every metal behaves the same way when subjected to friction and stirring. So, what metals can be friction stir welded, and what makes them suitable for this process?

This article explores the metals that are commonly, effectively, and sometimes experimentally used with friction stir welding. We'll look at how these metals respond to the process, the benefits and challenges they present, and the applications that have benefited from their successful joining through FSW.

Understanding the Friction Stir Welding Process

Before we explore which metals can be friction stir welded, it's important to understand how the process works.

Friction stir welding is a solid-state joining process where a rotating cylindrical tool with a specially designed pin and shoulder is plunged into the joint between two workpieces. As the tool rotates and moves along the seam, frictional heat softens the material without melting it. The softened materials are stirred together and forged under pressure to create a continuous, strong bond.

Because the metal never reaches its melting point, FSW results in fewer defects such as porosity, cracking, or distortion—common issues in conventional fusion welding. This makes it particularly effective for certain alloys that are difficult to weld by traditional means.

Aluminum Alloys: The Most Commonly Friction Stir Welded Metal

Aluminum and its alloys are by far the most widely used materials in friction stir welding. This is due to several key factors:

• Aluminum has a relatively low melting point, making it easier to soften without melting.

• It is widely used in industries that require lightweight yet strong materials.

• Aluminum is notoriously difficult to weld using fusion methods due to problems like hot cracking and porosity.

Series of Aluminum Alloys Suitable for FSW:

• 1xxx Series (Pure Aluminum): Excellent weldability due to low strength and high ductility.

• 2xxx Series (Aluminum-Copper): Generally difficult to weld by traditional methods, but FSW handles them well.

• 5xxx Series (Aluminum-Magnesium): High strength and corrosion resistance; commonly used in marine applications.

• 6xxx Series (Aluminum-Magnesium-Silicon): Very commonly friction stir welded, especially in automotive and construction applications.

• 7xxx Series (Aluminum-Zinc): High strength aerospace-grade alloys; FSW is often the only viable method for joining these.

Applications:

• Aerospace components (fuselages, fuel tanks)

• Automotive panels and chassis

• High-speed trains

• Shipbuilding and marine structures

• Consumer electronics and battery enclosures

Because of its reliability and minimal thermal distortion, FSW has become the preferred method for welding aluminum in high-performance applications.

Magnesium Alloys

Magnesium is the lightest structural metal and offers excellent strength-to-weight ratios, making it attractive in the automotive and aerospace industries. However, it has a tendency to oxidize and burn when subjected to high temperatures, which makes fusion welding risky.

Friction stir welding eliminates this concern because it keeps the material in the solid state, reducing the risk of ignition and improving weld integrity.

Applications:

• Lightweight structural frames

• Aerospace components

• Portable electronics and casings

• Automotive transmission housings

Magnesium’s softness also makes it easier to stir and forge, requiring lower tool forces compared to aluminum.

Copper and Copper Alloys

Copper has high thermal and electrical conductivity, which makes it essential in power generation, electronics, and heat exchangers. However, its high thermal conductivity poses a challenge in traditional welding because it quickly dissipates heat away from the weld zone.

Friction stir welding offers a solution by concentrating the heat through friction, allowing localized softening without excessive heat loss.

Benefits of FSW for Copper:

• No melting, so no risk of cracking or grain boundary segregation

• Excellent electrical conductivity retained

• Clean welds without oxidation or contamination

Applications:

• Busbars and electrical connectors

• Heat exchanger fins and tubing

• Electromagnetic shielding enclosures

While copper requires more robust tooling due to its hardness, its welds using FSW are typically very high quality.

Titanium and Titanium Alloys

Titanium is known for its high strength, corrosion resistance, and lightweight properties, making it essential in aerospace, medical, and chemical industries. However, titanium is notoriously difficult to weld using traditional methods due to its high reactivity and poor thermal conductivity.

Friction stir welding can be used for thin sections of titanium alloys, but it requires extremely durable tools, often made from polycrystalline cubic boron nitride (PCBN) or tungsten-rhenium alloys.

Challenges:

• High tool wear due to the hardness of titanium

• Narrow process window for proper heat generation

Applications:

• Aerospace panels and fittings

• Medical implants and surgical tools

• Heat exchangers in chemical industries

Although less common than aluminum or magnesium, titanium FSW is growing in high-value industries where joint strength and purity are critical.

Steel and Stainless Steel

Friction stir welding of steel is more complex due to its high melting temperature and hardness. However, with the use of advanced tooling materials such as PCBN, it is possible to friction stir weld carbon steels, stainless steels, and even some duplex grades.

FSW of steel is still largely confined to specialized applications due to high equipment and tool costs.

Applications:

• Oil and gas pipelines

• Railway components

• Automotive safety structures

• Pressure vessels and tanks

FSW allows for strong, ductile joints in steel without the risk of hard, brittle microstructures caused by rapid cooling in fusion welding.

Dissimilar Metal Joining

One of the most exciting capabilities of friction stir welding is its ability to join dissimilar metals—a process extremely difficult with fusion welding due to differences in melting points, thermal expansion, and metallurgical incompatibility.

Examples of Dissimilar Welds:

• Aluminum to Copper

• Aluminum to Magnesium

• Aluminum to Steel

• Titanium to Aluminum (experimental)

These joints are especially useful in applications like electric vehicles (joining aluminum casings to copper conductors) or aerospace assemblies (reducing weight while maintaining structural performance).

Experimental and Emerging Materials

While the most common friction stir welded metals are aluminum, magnesium, copper, titanium, and steel, researchers are constantly pushing the boundaries of what’s possible.

Materials under exploration:

• Nickel Alloys: Used in aerospace and power generation

• Superalloys: For high-temperature applications

• Metal Matrix Composites (MMCs): High strength, lightweight materials

• Advanced ceramics and hybrid materials: Using modified FSW techniques

These advanced materials often require specially designed tools and precise process control, but the potential benefits—such as lighter aircraft, more durable engines, and efficient energy systems—are enormous.

Key Considerations for Different Metals

Not every metal reacts the same to friction stir welding. Several factors determine the success of the weld:

• Thermal Conductivity: Affects heat dissipation and softening behavior.

• Hardness and Strength: Influence tool wear and required forces.

• Oxidation Tendency: Materials prone to oxidizing may need inert atmospheres or surface preparation.

• Alloy Composition: Determines flow behavior and joint properties.

• Thickness of Material: Thicker sections require more robust tools and greater force.

By understanding these properties, engineers can tailor the FSW process to the specific metal, ensuring optimal results.

Conclusion

Friction stir welding is an incredibly versatile technique that has transformed modern manufacturing. While aluminum is the most commonly used metal in FSW due to its lightweight nature and excellent weldability, many other metals—including magnesium, titanium, copper, and steel—are also highly suitable. Each of these materials brings unique benefits, such as magnesium’s lightness, titanium’s strength, copper’s conductivity, and steel’s structural reliability. Moreover, FSW’s growing capability to join dissimilar metals and experimental alloys expands its application across advanced engineering sectors.

As industries push for lighter, stronger, and more efficient products, friction stir welding continues to stand out as a clean, reliable, and high-integrity joining method. From aerospace and automotive to electronics and energy, FSW plays a vital role in shaping the future of manufacturing. For engineers, manufacturers, and innovators alike, understanding which metals can be friction stir welded is key to unlocking new possibilities and achieving superior performance in modern fabrication.