Everything you need to know about aluminum 3D printing

Only very recently have AM-specific aluminum alloys begun to gain adoption in the market. The first and most popular one is Scalmalloy, which was developed and is currently marketed by aerospace specialists APWORKS (now part of Premium AEROTEC). Known service providers offering Scalmalloy manufacturing capabilities include some of the largest metal AM service providers in the world, such as 3T and Zare (acquired by BEAMIT), Sauber Engineering, Metron, https://www.3dprintingbusiness.directory/company/toolcraft/, PolyShape (now part of AddUp), Pankl and Quadrus Corporation.

Another popular aluminum alloy for AM is A20X, which was explicitly developed for additive manufacturing and can offer tensile strength up to 511 MPa, yield strength up to 440 MPa, and elongation at fracture up to 13%. A20X is now commercialized globally by ECKART, part of the ALTANA Group, after it acquired the original material developer AMT.

MX3D, the Dutch leader in WAAM technology, known for several high-profile applications, has also qualified a wide range of aluminum materials for its technology (available both via production services and the M1 hardware systemsì). These include AlSi10Mg (4046) and AlSi7Mg (4018) in wire form as well as 5356, and 5087. WAAM3D, a UK company that recently entered the market with the advanced and highly automated roboWAAM system, also offers aluminum wire, both 2319 and AlMgSc (with scandium, like aerospace-grade AA5028 but with a higher scandium content). The company supplies them in spools as large as 150 Kg, for extra-long production runs for both CMT-WAAM (cold metal transfer) and PTA-WAAM (plasma transferred arc) processes. WAAM3D also lists 2024 and 5087 alloys as available for both CMT and PTA WAAM processes but reports low demand for them.

Before the Russian invasion of Ukraine, RUSAL, one of the world’s largest aluminum manufacturers, launched the ALLOW series of aluminum products for AM which include both casting alloys and several alloys developed specifically for AM processes and optimized for sustainability and low energy demands. Among these are RS-230 AlCu (a hot crack–resistant 2xxx series alloy) and RS-390 AlSiNi alloys, which are suitable for applications up to 250 °C; and RS 507 AlMg and RS-553 AlMgSc alloys, which are corrosion-resistant, high-strength materials marketed at a significantly lower price than Scalmalloy. While the threatened full ban on Russian aluminum has not gone into effect, it is not clear at this time what the business perspectives for RUSAL aluminum powders are, even as the company produces as much as 6% of the world’s aluminum.

In 2020, French company Constellium launched Aheadd, a new generation of optimized high-performance aluminum powders for L-PBF. Among these, Aheadd CP1 (Al-Zr-Fe) is the preferred solution when high conductivity and increased productivity are required. Aheadd HT1 (Al-Mn-Ni-Cu-Zr) is a solution for high temperature and strength requirements.

Along with A20X, ALLOW and Aheadd, Canadian power manufacturer Equispheres launched Performance, Precision and Production aluminum powders for AM (which are both the brand names for each product and their intended uses). The company developed perfectly uniform, perfectly spherical powder improving process reliability, speed of production and part performance in AM, targeting opportunities for high-volume, lightweight AM parts. Equispheres has also partnered with TRUMPF, Lockheed Martin, Aconity3D and Morf3D to accelerate development.

Aluminum binder jetting

Equispheres aluminum powder is sinterable without modifications or additives. This provides a performance advantage on binder jetting printer platforms. With the binder jetting process lauded as the breakthrough needed to bring additive manufacturing to the next level, these inherently sinterable aluminum powders will open the doors for mass production of lightweight parts.

This brings us to the interesting topic of aluminum binder jetting. As metal PBF processes become more and more productive through larger, faster and more automated systems, the adoption and demand for aluminum alloys are expected to grow significantly. However, a major challenge to the widespread adoption of aluminum in AM is that the processes targeting large batch and serial production via AM, which would benefit the most from aluminum’s lower cost, are high-throughput binder jetting processes. In terms of materials development, these processes generally benefit from the ability to rapidly adapt metal materials initially envisioned for and used in MIM processes. Aluminum and its alloys are not among these

In binder jetting as in conventional MIM, the metal powder is first mixed with a binder in order to make it moldable or to build the part additively. The green part is then sintered in a furnace. The binder is removed and the oxide layer is reduced with heat. The metal powders join to form a solid object. Aluminum is challenging to sinter as the oxide layer surrounding the particles can only be removed at extremely high temperatures, while aluminum has a relatively low melting point, which restricts the maximum sintering temperature. It is therefore very challenging to remove the oxide layer on the aluminum powder before the entire metal piece has melted.

Solutions to this issue have been explored for several years, but full commercialization of aluminum as binder jettable materials has remained beyond reach. Today, however, this may be changing. In early 2021, both binder jetting companies Desktop Metal and ExOne (now merged) separately achieved major breakthroughs in the sintering of aluminum 6061 for parts produced by binder jetting technology.

The new powder from Desktop Metal enabled the sintering of unadulterated 6061 aluminum and represents a significant improvement over prior techniques used to sinter aluminum, which required coating powder particles, mixing sintering aids into powder, using binders containing expensive nanoparticles or adding metals such as lead, tin and magnesium. Critically, Desktop Metal’s powder also enabled compatibility with water-based binders and has a higher minimum ignition energy (MIE) relative to other commercially available 6061 aluminum powders, resulting in an improved safety profile. Desktop Metal and Uniformity Labs are working to qualify the powder and scale production for commercial release. Once fully qualified, Uniformity 6061 aluminum will be available for use with the Desktop Metal Production System platform.

The potential of aluminum as a material for binder jetting is significant and Ricoh has so far centered its entire metal AM strategy on this specific segment. Although its technology is not yet marketed, it has already proven the ability to produce complex and fairly large parts.

Aluminum for kinetic consolidation

Another Australian company, SPEE3D, supports high-speed, large-format 3D printing of (non-spherical) aluminum powders (including 6061, 5056, and 7075) via its Supersonic 3D Deposition technology, a type of kinetic consolidation (aka cold blown powder). This is the name given to the patented process in which a rocket nozzle accelerates air up to three times the speed of sound, into which metal powder is injected and then deposited onto a substrate maneuvered by a six-axis robotic arm. In this process the sheer kinetic energy of the particles hitting each other causes the powders to bind together to form a high-density part with metallurgical properties superior to casting.

Wire-based aluminum 3D printing

Aluminum alloys could also prove to be valuable and very cost-effective materials for high-throughput WAAM (wire arc additive manufacturing) processes. In fact, today, the majority of aluminum alloys are printable only via wire-based technologies. The use of various aluminum alloys across various types of WAAM technologies is also an actively researched field. Recent work shows that the most promising alloys are AlLi, AlCu, Al–Mg, AlZnMgCu, AlCuMg, AlSiMg, AlMgSi and AlMgMn/AlMg5Mn (these are of particular interest due to their high strength and corrosion resistance). Several wire-based metal DED companies around the world target aluminum as a key material.

AML3D, an Australian company marketing WAM (Wire Additive Manufacturing) technology through the Arcemy systems, supports the use of several aluminum alloys in wire form, specifically 2319, 4043, 5183, 5183 (0.2%Sc), 5356, and 5087. The WAM process is characterized under the 3D printing standards for Direct Energy Deposition, Compared to other wire-feed-stock metal printing techniques such as Electron Beam, Wire Fed Laser and Laser sintering processes, WAM can be used to print metal parts in an open free-form fabrication environment using a localized inert gas, reducing fabrication costs while improving material properties.

While aluminum support is often part of WAAM companies’ material strategies, it is also interesting to note that Meltio, a rapidly growing company marketing high-speed, low-cost, mainly metal wire-based AM systems, does not currently offer aluminum among its supported materials. It is also worth noting that Xerox recently abandoned its ElemX project, which was based on a liquid metal printing approach and saw aluminum as the primary material for the technology’s application and growth strategy.

In the US, MELD, a growing startup with a key interest in defense applications, developed a solid-state process (meaning the material does not reach the melting temperature during the process) to produce high-quality materials and parts with low residual stresses and full density with significantly lower energy requirements than more conventional fusion-based processes. The MELD process is capable of printing large metal parts at a scale not yet seen in the metal additive market and deposits material at least 10 times faster than fusion-based metal additive processes. MELD’s first commercially available machine, B8, uses solid bars of metal however different powders can also be combined to make a Metal Matrix Composite (MMC) such as Al-SiC, Al-Fe, Al-W, Al-Mo.

Among material suppliers, the AM materials portfolio of voestalpine Böhler includes a non-specified aluminum wire for WAAM. However, the use of WAAM with aluminum materials is still often limited by defects such as porosity and solidification cracks, which can severely limit the mechanical properties of the components, such as component strength or ductility. Recently a startup called Fortium Metals, which builds on the experience of Elementum 3D, entered the market focusing specifically on metal wire materials for additive manufacturing. Among its capabilities, the company offers “ideal metallurgy for welding the unweldable”, including 1xxx, 2xxx, 6xxx, and 7xxx series aluminum, by solving hot tearing and hot cracking issues.

Aluminum applications in AM

As metal developers and manufacturers introduce more AM-specific aluminum and aluminum alloy materials, the applications for the metal continue to grow. Today, though application potential remains largely untapped, there are some areas where aluminum AM is progressing.

Scalmalloy was developed specifically for aerospace applications and has the properties to back it up. The aluminum-magnesium-scandium powder alloy has a high strength-to-weight ratio, good ductility and corrosion resistance. Used in combination with topology optimization, the material can deliver lightweight, high-performance aircraft components. It is also worth mentioning that the aluminum alloy was used by APWORKS in the creation of the Light Rider, a 3D printed motorcycle back in 2016.

In the automotive and motorsport worlds, aluminum alloys are being implemented with 3D printing technologies. A notable case is the window guide rail on the BMW i8 Roadster. Made of aluminum alloy, the metal component weighs less than the injection-molded plastic part that is normally used but is still considerably stiffer. Its importance has already been recognized with an Altair Enlighten Award. Another key application saw Mercedes Benz 3D print one of the very first spare parts for the Trucks division back in 2017. Another key initiative, also dating back to 2017, saw Daimler, EOS and Premium Aerotec partners on the NextGen AM project whose main objective was to advance the automation of.the industrial 3D printing process, with a specific focus on the qualification of aluminum for use in industrial 3D printing. The project was brought to an end in 2019 as the companies said they had gained significant insights.

Motorsports is another high-growth area for AM, and aluminum can play a role. In 2020, Formula 1 approved the use of two Elementum 3D aluminum powders (A6061-RAM1 and A2024-RAM2) for the 2021 racing season. Elementum 3D’s A6061-RAM2 alloy was also used by aerospace startup Masten Space Systems to produce a 3D printed e-pump.

The luxury and hypercar automotive segment continues to be the most receptive to aluminum 3D printing, especially (at this time) for L-PBF applications. The most notable is the ongoing collaboration between Divergent and SLM Solutions on the Czinger21 supercar, which features as many as 350 3D printed parts on each vehicle, the majority of which are made using aluminum alloys.

Also notable in the automotive space is the German EDAG Group, which in 2020 developed an aluminum alloy for 3D printing automotive parts in cooperation with eight partners. The metal, CustAlloy, is engineered to be “crash-proof” and has higher strength and elongation at break than other aluminum AM materials. Looking at more widespread use in mass market automotive, Ford and binder jetting specialist ExOne (now part of Desktop Metal) developed a way to 3D print aluminum 6061 using binder jetting, as well as to sinter it. The process, capable of producing parts with 99% density, is still patent pending.

There is also a myriad of applications for aluminum alloys in the industrial sector, including the production of heat exchangers and heat sinks. Australian AM company Conflux Technology demonstrated how it could produce more efficient heat exchangers using AM and aluminum alloys. Specifically, the company showed a 3D printed heat exchanger built using the EOS M 290 3D printer and EOS’ AlSi10Mg material. The now-patented heat exchanger has various applications across a range of industries, including aerospace, automotive, oil & gas, chemical processing and microprocessor cooling.