Researchers 3D-Print Super-Strong Aluminum to Solve Longstanding Welding Problem

　　Researchers have made a significant breakthrough in metal additive manufacturing with a new technique for successfully 3D printing high-strength aluminum that makes previously unweldable metals weldable.

The technique—developed at Malibu, Calif.-based HRL Laboratories—solves a 100-year old problem that paves the way for using additive manufacturing to print a number high-strength engineering-grade alloys. These metals can be used in aircraft and automobile parts in unprecedented ways, according to the team in the lab’s Sensors and Materials Laboratory.

“We’re using a 70-year-old nucleation theory to solve a 100-year-old problem with a 21st century machine,” said Hunter Martin, who co-led the team with Brennan Yahata. The two are engineers in the lab as well as PhD students at the University of California, Santa Barbara.

In addition to being able to 3D print types Al7075 and Al6061 of high-strength aluminum alloys, the technique—which involves a new way to treat the powders used in printing metals—also can be applied to using additive manufacturing to produce high-strength steels and nickel-based superalloys that have so far been difficult to process this way, Martin said.

Moreover, because the additive-manufacturing method includes melting and solidification that is essentially the same process of welding, it also can be used to make previously unweldable alloys weldable, he added.

The team—including Martin’s co-engineer Brennan Yahata and their mentor, Professor Tresa Pollock of UC Santa Barbara—published a paper on their work in the journal Nature.

To use additive manufacturing to print metals, thin layers of alloy powders are heated with a laser or other direct heat source to melt and solidify the layers. Typically, if high-strength aluminum alloys such as A17075 and AL6061 are used in this type of process, the parts the emerge suffer substantial hot cracking, which means the finished metal product can easily flake apart.

To correct this problem, the HRL team used a nanoparticle functionalization technique that adds zirconium-based nanoparticles to high-strength unweldable alloy powders. They fed the powder into a 3D printer, which layered it and laser-fused each layer to construct a solid, 3D object.

Key to the method is that during melting and solidification of the metal, the nanoparticles act as nucleation sites for the desired alloy microstructure, according to researchers. This prevents hot cracking and allows for the alloy to retain its full strength in the part that’s manufactured.

“Our first goal was figuring out how to eliminate the hot cracking altogether,” Martin explained. “We sought to control microstructure and the solution should be something that naturally happens with the way this material solidifies.”

Other benefits to the method are that it can scale and uses low-cost materials, making it both applicable to high-volume production as well as cost-effective, researchers said.