Materials

HRL 3D prints high-strength aluminum solving ages-old welding problem using nanoparticles

HRL has developed a 3D printing technique for high-strength aluminum alloys. The additive manufacturing method can used with variants of Al7075 and Al6061. The work opens the door to additive manufacturing of engineering-relevant alloys.

Essentially, the researchers have taken a non-weldable metal, and made it weldable. This is important because while 3D printing has many applications in aerospace, some of these components must be joined using rivets – rather than welded – due the materials involved.

Aluminum alloys are the focus of the newly published research paper 3D printing of high-strength aluminium alloys and is published in the September 21, 2017 issue of Nature. The researchers note that the method can be applied to additional alloy families such as high-strength steels and nickel-based superalloys difficult to process currently in additive manufacturing.

Preventing hot cracking when 3D printing metal

When working with non-weldable aluminum alloys such as Al7075 or AL6061, 3D printing metal in a high energy environment using lasers results in that parts that suffer severe hot cracking, “a condition that renders a metal part able to be pulled apart like a flaky biscuit” says HRL.

“Our first goal was figuring out how to eliminate the hot cracking altogether. We sought to control microstructure and the solution should be something that naturally happens with the way this material solidifies,” Hunter Martin, who co-led the team with Brennan Yahata, said.

“HRL’s nanoparticle functionalization technique solves this problem by decorating high-strength unweldable alloy powders with specially selected nanoparticles. The nanoparticle-functionalized powder is fed into a 3D printer, which layers the powder and laser-fuses each layer to construct a three-dimensional object.  During melting and solidification, the nanoparticles act as nucleation sites for the desired alloy microstructure, preventing hot cracking and allowing for retention of full alloy strength in the manufactured part.”

Scalable and employs low cost materials

The correct nanoparticles for aluminum were found to be zirconium-based nanoparticles. Citrine Informatics was used to sort through the range of particle properties available. “Using informatics was key,” said Yahata. “The way metallurgy used to be done was by farming the periodic table for alloying elements and testing mostly with trial and error. The point of using informatics software was to do a selective approach to the nucleation theory we knew to find the materials with the exact properties we needed. Once we told them what to look for, their big data analysis narrowed the field of available materials from hundreds of thousands to a select few. We went from a haystack to a handful of possible needles.”

HRL believe the technique opens a new chapter in additive manufacturing of metals for research, industry, and defense.

The research authors are Jacob Hundley, Justin Mayer, and Tobias A. Schaedler. 3D Printing Industry recently asked Dr. Schaedler a few questions about the labs 3D printed ceramic engine part and how 3D printing enables, “lower cost, faster fabrication and new designs that are impossible or hard to realise with conventional manufacturing approaches”.

Materials key to additive manufacturing projects

Aerojet Rocketdyne recently passed several important milestones in the development of the 3D printed AR1 rocket engine. The AR1 is made from Mondaloy™ a nickel-based superalloy co-invented by Monica Jacinto of Pratt & Whitney Rocketdyne. The AR1 is intended to replace the Russian made RD-180 rocket engine that the U.S. currently depend upon for military launches.

In Germany, Fraunhofer ILT recently announced the, “SLM in Green” project focused on additive manufacturing with copper. The project aims to produce 3D printed metal components with “notably higher detail resolution as well as greater cost efficiency”.

The full paper can be read here.

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