HRL Creates Method To 3D Print High-Strength Aluminum

HRL Laboratories, a combined research entity for advanced materials owned by the Boeing Company and General Motors, has come up with a way to use 3-dimensional printing to create parts made of high-strength aluminum, including AI7075 and AI6061. This method also creates a pathway towards making products from other additive-intense alloys with various metals and welds, including high-strength steels and superalloys.

High-strength alloys are becoming very common in automotive manufacture and are the main pathway of research for aircraft materials as well. High-strength alloys are lightweight and strong, but often very expensive as well. HRL’s new 3D printing method could change that.

Additive manufacturing of metal alloys via selective laser melting. The central schematic represents an overview of the additive manufacturing process, whereby a direct energy source (laser or electron beam) melts a layer of metal powder (yellow), which solidifies (red to blue), fusing it to the previous (underlying) layer of metal (grey). a, Conventional Al7075 powder feedstock. b, Al7075 powder functionalized with nanoparticles. c, Many alloys including Al7075 tend to solidify by columnar growth of dendrites, resulting in cracks due to solidification shrinkage. d, Suitable nanoparticles can induce heterogeneous nucleation and facilitate equiaxed grain growth, thereby reducing the effect of solidification strain. e, Many alloys exhibit intolerable microstructure with large grains and periodic cracks when 3D-printed using conventional approaches, as illustrated by the inverse pole figure. f, Functionalizing the powder feedstock with nanoparticles produces fine equiaxed grain growth and eliminates hot cracking. g, A 3D-printed, topologically optimized Al6061 piston on the build plate. h, 3D-printed Al7075 HRL logo. Martin et al.

Additive manufacturing of metals typically begins with alloy powders that are applied in thin layers and heated with a laser or other direct heat source to melt and solidify the layers. Normally, if high-strength unweldable aluminum alloys such as Al7075 or AL6061 are used, the resulting parts suffer severe hot cracking—a condition that renders a metal part able to be pulled apart like a flaky biscuit.

HRL solves this problem by decorating high-strength unweldable alloy powders with specially selected nanoparticles— nanoparticle functionalization. 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.

Because melting and solidification in additive manufacturing is analogous to welding, HRL’s nanoparticle functionalization can also be used to make unweldable alloys weldable. This technique is also scalable and employs low cost materials. Conventional alloy powders and nanoparticles produce printer feedstock with nanoparticles distributed uniformly on the surface of the powder grains.

The HRL methods and findings were published in the journal Nature: http://dx.doi.org/10.1038/nature23894