What weld is required for aluminum?
The weld most commonly used for aluminum is TIG (GTAW) welding, typically performed with AC current and a suitable filler rod; MIG (GMAW) is also used for production runs, while friction stir welding is employed for high-strength joints in thicker sections.
Overview of aluminum welding
Aluminum behaves differently from steel: it forms a protective oxide layer that must be broken and cleaned during welding, and its high thermal conductivity requires appropriate heat control. The choice of welding process depends on alloy family (1xxx, 2xxx, 5xxx, 6xxx, 7xxx), thickness, joint design, and the final properties required. This article outlines the main options and when to use them.
Common welding methods for aluminum
Three methods dominate most aluminum fabrication: TIG welding for precision work, MIG welding for speed on thicker sections, and friction stir welding for high-strength solid-state joints. Each method has advantages and constraints depending on alloy, thickness, and desired finish.
- TIG (GTAW) welding: The go-to method for clean, high-quality aluminum welds. Uses a tungsten electrode with argon shielding; for aluminum, AC current helps to break the oxide layer. Common filler alloys are 4043 (Al-Si) or 5356 (Al-Mg), chosen based on the base alloy.
- MIG (GMAW) welding: Fast, adaptable for production, often used on thicker sections. Requires a spool gun or push-pull feed for aluminum wire and typically uses AC with suitable filler (4043 or 5356). Shielding is argon, sometimes with small helium admixture for penetration.
- Friction stir welding (FSW): A solid-state process that fuses aluminum without melting, yielding high-strength joints suitable for thick plates and complex assemblies used in aerospace and automotive sectors. Requires specialized equipment and joint fixturing; no filler metal is typically needed.
In practice, TIG is chosen for precision and cosmetic quality, MIG for speed and weight efficiency on thicker parts, and friction stir welding for high-strength joints in thick aluminum where melting would be detrimental.
Filler metal choices and joint design
The filler alloy you choose affects the weld's strength, corrosion resistance, and compatibility with the base metal. Common choices include 4043 for many 6xxx alloys and 5356 for 5xxx alloys; 4047 can be used for certain 6xxx or to improve crack resistance in some joints, but it can increase shrinkage and porosity in some conditions. Joint design—root gaps, fit-up, and shielding gas coverage—also plays a critical role in weld quality, especially for thinner sheet metal where burn-through and porosity are concerns.
Choosing the right process by thickness and alloy
Material thickness and alloy series guide process selection. The following guidelines summarize typical choices by thickness and application.
- Thin sheets and detail work (approximately 0.5 to 3 mm): TIG welding with AC is preferred for clean, precise welds; filler choices are often 4043 for 6xxx alloys or 5356 for certain 5xxx alloys; ensure proper purge when welding closed sections to prevent porosity.
- Medium thickness (roughly 3 to 6 mm): TIG remains common for high-quality welds, but MIG can be used for faster production. Choose filler per alloy; manage heat input to avoid burn-through and distortion.
- Thick sections (greater than 6 mm): MIG or flux-cored welding can provide higher deposition and speed; for very thick or critical joints, friction stir welding can be advantageous; TIG is possible but slower and more heat-intensive.
Specialized methods such as laser welding or hybrid processes are used in high-end applications to balance speed, strength, and precision. Always verify welding procedure specs for the specific aluminum alloy and thickness you are working with.
Summary
Aluminum welding centers on TIG for precision and MIG for production, with friction stir welding offering a solid-state alternative for thick, high-strength joints. The key is to match the alloy family, thickness, and joint design with the appropriate process, filler, and shielding gas, while observing best practices for cleanliness and heat management. Always consult the material supplier and welding procedure specifications for optimal results.
What type of welding is used for aluminum?
The most common types of welding used for aluminum are Gas Tungsten Arc Welding (GTAW) / TIG and Gas Metal Arc Welding (GMAW) / MIG. TIG is preferred for achieving high-quality, clean welds, especially on thinner materials, while MIG is a faster process that works well for thicker aluminum. Other processes include laser beam, electron beam, resistance, and shielded metal arc welding (SMAW).
TIG welding
- Best for: Thinner sections and high-quality, precise welds.
- Process: Uses a non-consumable tungsten electrode and an inert shielding gas like argon to create the weld.
- Details: The welder manually feeds the filler material into the puddle. TIG welding requires AC (alternating current) power to break up the aluminum's oxide layer.
MIG welding
- Best for: Thicker aluminum and faster welding speeds.
- Process: Uses a continuously fed wire electrode and an inert shielding gas to join the metals.
- Details: A spool gun or push-pull gun is often necessary due to aluminum wire's softness. A 100% argon or an argon/helium blend is used as the shielding gas, as CO2 can cause issues with aluminum.
Other welding types
- Laser beam and electron beam welding: Can be used for aluminum and are often utilized in high-tech industries.
- Resistance welding: Also a viable option for joining aluminum.
- Shielded metal arc welding (SMAW) or "stick" welding: Can be used for aluminum alloys, but is more common for steel.
- Friction welding: A solid-state process that generates heat through friction and is effective on hard-to-weld alloys.
Is 4043 or 5356 better for cast aluminum?
This is because 4043 has better fluidity, lower cracking sensitivity, and is more compatible with most cast aluminum alloys. 5356 is typically used for wrought aluminum alloys and may cause hot cracking when used on cast aluminum.
Do you need a special MIG welder for aluminum?
Look for a MIG welder specifically designed for aluminum or one with the capability to weld aluminum. These machines typically have features like: Spooled aluminum wire: Solid aluminum wire requires a special spool with a larger inner diameter to accommodate the softer aluminum wire.
Is TIG or MIG better for aluminum?
Conclusion. MIG and TIG are two very different processes, but both can weld aluminum. While MIG can handle aluminum using a DC, the TIG process requires the use of AC. If you plan to weld aluminum often or want to achieve the highest quality joint, AC TIG is irreplaceable.
