Which Aluminum Alloys Are Most Commonly Used in WAAM for Structural Uses?

Primary Alloys: Excellent Weldability and Corrosion Resistance

The aluminum alloys most commonly deployed in Wire Arc Additive Manufacturing (WAAM) for structural applications are selected primarily for their superior weldability, strength-to-weight ratio, and resistance to solidification cracking. The 5xxx series (Al-Mg) alloys, particularly ER5183 and ER5087, are foundational choices. Their magnesium (Mg) content provides solid-solution strengthening without forming brittle phases that are prone to cracking during the rapid thermal cycles of WAAM. These alloys offer excellent as-welded strength, outstanding corrosion resistance—especially in marine environments—and are widely used for large-scale structural components in sectors like marine and transportation.

Versatile, Heat-Treatable Alloys for Enhanced Strength

For applications requiring higher specific strength, the 6xxx series (Al-Mg-Si) alloys are prevalent. ER4043 (AlSi5) and ER4943 are frequently used filler wires. The silicon (Si) content improves fluidity, reduces hot cracking, and provides good weld bead contour. While their as-deposited strength is lower than 5xxx alloys, they respond well to post-WAAM heat treatment (solutionizing and artificial aging), enabling significant strength recovery and enhancement. This makes them suitable for structural frames and components in aerospace and aviation, where post-process thermal treatment is standard.

High-Strength Aerospace-Grade Alloys

Driven by demand from the aerospace sector, there is significant R&D focus on processing high-strength 2xxx series (Al-Cu) and 7xxx series (Al-Zn) alloys via WAAM. Alloys like 2024 (Al-Cu-Mg) and 7075 (Al-Zn-Mg-Cu) are highly desirable for their exceptional strength. However, their WAAM processing is challenging due to high susceptibility to solidification cracking and significant porosity. Successful deposition often requires precise control over the shielding atmosphere, specialized wire chemistries with grain refiners (e.g., Ti, Zr), and integrated interpass cooling. Successful builds typically must undergo a strict post-deposition heat treatment and Hot Isostatic Pressing (HIP) to achieve optimal mechanical properties and density for critical structural uses.

Alloy Selection and Post-Process Considerations

The selection of an aluminum alloy for structural WAAM is a balance between weldability, required mechanical properties, and the feasibility of post-processing. For non-heat-treatable 5xxx series alloys, properties are largely set during deposition, making process control paramount. For heat-treatable 2xxx, 6xxx, and 7xxx series, the WAAM process must produce a sound, crack-free preform that can reliably respond to subsequent thermal cycles. Regardless of the alloy, most WAAM-produced aluminum structures require final CNC machining to achieve dimensional accuracy and surface finish, as the process yields a near-net-shape part. The convergence of WAAM with traditional aluminum 3D printing and subtractive techniques enables the manufacturing of optimized, lightweight structural components.