Aluminium Additive Manufacturing: How a new generation of alloys will fuel industry growth

Aluminium alloys have been a target material since the introduction of metal AM technologies. However, in the nascent era of Additive Manufacturing, there was a significant issue to overcome: virtually all the metal AM machines used lasers. These were relatively low-powered CO₂ lasers, and those unfamiliar with the physics of laser-materials interactions should think of aluminium as being a mirror, in that it reflects a lot of light at the output wavelength of a CO₂ laser (10.6 µm). In fact, around 98% of light energy is reflected by aluminium at this wavelength.

To effectively work with aluminium required more available energy, and higher-energy CO₂ lasers were fairly big beasts back in the mid-1980s. This made it impractical to develop Laser Beam Powder Bed Fusion (PBF-LB) machines for metals such as aluminium. Further, this is before considering that the early attempts to process any metal relied on sintering polymer-coated metal powders, rather than the full melting of the metal.

Despite the apparent technological roadblocks, aluminium has remained a highly sought-after material in AM and has regularly been the most-searched-for material on the Metal AM website. In fact, in the month prior to this article going to press, queries relating to aluminium were amongst the highest of all searches on the website – and four times higher than the second most popular material. Looking back over the past couple of years, aluminium has always been in the top ten search terms.

Does this mean that aluminium accounts for the leading applications in metal AM? Despite the interest, the answer to that is never going to be so straightforward. Most other industry reports and statistics would point to either stainless steel, titanium, or potentially nickel-based alloys being the most common. Why is this?

When rapid prototyping using metal started to become popular there was a switch to fibre lasers. However, there was still considerable difficulty in processing aluminium because the available power from these machines was still too low; typical maximum outputs were only 150-200 W. In reality, it is probable that a combination of relatively low power together with over-sized focused laser spot diameters was the cause for the poor early results of aluminium powders. This led to aluminium alloys being sidelined in favour of titanium alloys and nickel-based superalloys. One thing we know for sure, though, is that aluminium became more and more popular as PBF-LB processes matured and machines began to feature 200 W and 400 W lasers.

Early barriers to the adoption of aluminium

The main contributing factor to the slow adoption of aluminium was probably based on the availability of desired alloys. Early adopters of AM were in sectors that needed high-performance materials; for aluminium, this meant 2000 and 7000 series wrought alloys. Instead, the first aluminium alloy that was introduced directly by AM machine OEMs was AlSi10Mg. As someone who was intimately involved with developing this part of the AM sector, I have clear memories of the response of prospective AM parts users when I first introduced the AlSi10Mg alloy: unfamiliarity and confusion. The intended market simply did not recognise this alloy, and knew nothing about its performance or capabilities. Anyone in metal AM sales at that time will know that it was like trying to push water up a hill.

The early adopter of metal AM with the most interest in aluminium was the aerospace sector, where all of the Tier 1 suppliers and OEMs will insist on certainty around the Technical Readiness Levels (TRL) of any material to be used in an aircraft. Hence, introducing a new material like AlSi10Mg on top of a completely new method of production was never going to be easy. It was, however, far easier for sales teams to focus on other recognisable materials that were well-suited for aerospace and for which there were target applications, namely Inconels and titanium alloys. This situation did not change significantly until the introduction of F357 (AlSi7) and 6061.

Since the introduction of AlSi10Mg for AM, considerable groundwork has been carried out, in particular in the past five years. So, now that data do exist to underpin the use of such alloys in AM and international standards are being made available by ASTM and SAE International, these alloys will probably gain traction at a faster rate.

A second factor that may have been partly responsible for diverting the early AM sector’s interest away from aluminium was a little quirk that AM introduced to design theory and materials selection. To explain, let’s look at why aluminium gained popularity as an engineering material in the first place.

In the context of aerospace, aluminium was attractive due to its ability to produce lighter structural components. However, the drawback to using these sorts of lighter, lower-strength alloys was the need to increase individual part sizes in order to achieve the desired stiffness or load-bearing capacity. At the time, however, there weren’t any recognised grades of aluminium that engineers could work with, leading instead to a bit of a frenzy for titanium. While it is as strong as steel, titanium’s biggest drawback when it was introduced was its price.

This all meant that – for most applications – there wasn’t a sensible economic solution to lightweight AM parts. It was a very pervasive belief, too; I believed it until I had my first conversation with a founder of the company which would go on to change the world of hydraulics using AM. This company had almost immediately identified that the design freedom that AM brought about meant that lightweight designs could also be made from highly stiff, substantially cheaper materials like steel. For me, it was a light bulb moment. As the message spread that AM was enabling optimally designed steel parts, the appeal of aluminium faded a little.

The third and final possible reason for the slow adoption of aluminium was the fear of explosions – not necessarily catastrophic ones, but enough to cause injury, damage equipment, labs, or the immediate work environment. This fear was amplified by a degree of misinformation and a vocal, safety-conscious minority. As a result, explosion risk warnings were often plastered on any areas where aluminium powder might come into contact with air, leading many organisations to avoid working with the material altogether. Those that did eventually adopt it typically waited until either self-imposed safety regimes could be proven, or they were reassured by the high-level data and analysis that showed the risk of explosion may have been overstated by some.

Let’s be clear: health and safety is very important, and things can go disastrously wrong when rules are broken. Regardless, hearsay and fear of the unknown should never be a reason to stifle progress.

AlSi10Mg as a driver of early success

Fortunately, sufficient numbers of determined (or simply curious) people allowed AlSi10Mg to start to gain ground. Once people were able to identify this alloy as equivalent to the UK casting alloy LM9, or A360 in the USA, it became easier to talk about it as a suitable alloy for AM. Furthermore, with a little bit of detective work, it was identified as chemically similar to grades of aluminium already common in aerospace, resulting in a notable increase in the development of powders and laser parameters for these other alloys between 2012 and 2015. In many cases, it was realised that you could use the same laser process parameters for all these similar alloys, which included L169 (A357), AlSi7Mg (F357), and AlSi12Mg.

Although it has been proven many times over that these apparently subtle differences in the alloying contents can result in slightly different behaviours during melting, solidification, and cooling, it is in the subsequent post-processing after the build itself that has the most significant effect in determining final materials properties. Once the AM community understood that these alloys required more than just a simple stress-relieving step, and that blindly following previously used T6 types of heat treatment was not going to yield the desired outcome, this class of Al-Si alloys started to produce good results – and in some groundbreaking applications. We are all very familiar with the satellite TMTC brackets produced for Airbus Defence & Space, first featured on www.metal-am.com in March 2015.

Once AlSi10Mg had gained acceptance, and users understood that it was an age-hardenable alloy, the industry realised that it needed a baseline to measure everything against. This was especially important given that there was no realistic alternative in the form of other desired higher strength alloys, so the aerospace sector began to focus on fully characterising both AlSi10Mg and the F357 alloys.

Several years of intense data gathering have been conducted up to now – and from all over the world. It’s also likely that the first standards for these alloys are either in publication or very close to completion.

Specific challenges to the AM processing of aluminium

One small and rather restrictive group of alloys was never going to be enough, and there has always been the question of how to meet higher strength requirements. Take, for instance, the aerospace and motorsports communities, which were familiar with 2000 series and 7000 series wrought aluminium alloys and continuously demanded something similar, if not exactly the same.

2000 Series (predominantly Al-Cu alloys) and 7000 series (Al-Zn-Mg alloys) have been widely used where strength-to-weight ratios are critical, and both exhibit excellent machinability and relatively good corrosion resistance. However, they are known to be challenging to weld due to issues such as hot cracking, which is driven by significant thermal stresses during solidification as a result of their high alloying content.

In the context of AM, porosity is a significant issue in achieving fully dense parts. These alloying elements, as a consequence of the high reflectivity and thermal conductivity of aluminium, can lead to vaporisation and entrapment of gas pores. These are issues faced routinely in the PBF-LB and wire-arc Directed Energy Deposition (DED) processes (Fig. 5).

There are also several general challenges to be addressed when processing all aluminium alloys:
The formation of very stable oxide layers that can interfere with the AM process, from melting to bonding, particularly in PBF-LB and DED

• Close attention needs to be paid to thermal management to avoid overheating and resultant serious defects and warping
• When alloyed with light elements, the alloys may be unsuitable for some AM processes, such as Electron Beam Powder Bed Fusion (PBF-EB)
• Moisture, especially in PBF

All of the above challenges highlight the need for ongoing research and development to optimise alloy compositions and process parameters, specifically to improve the Additive Manufacturing process itself and the performance of aluminium alloys therein.

Early alloy innovation

Laser Beam Powder Bed Fusion dominated the early use of aluminium in AM, and, amidst the uphill struggle to convince the world that AlSi10Mg would be a good starting material, Scalmalloy emerged. Scalmalloy entered the AM sector as a completely new alloy. While everyone else was preoccupied with trying to achieve equivalence to 2000 and 7000 series alloys, the team at the then Airbus Group’s Innovation Works derived its solution from 5000 series (Al-Mg alloys). By adding scandium and zirconium together, they were able to completely change the precipitation-strengthening characteristics of these alloys while maintaining the excellent corrosion resistance that 5000 series alloys are noted for.

However, this new alloy has taken a rather long time to gain popularity, stemming mostly from scepticism – maybe even envy. This was not aided by the fact that it seemed impossible to get hold of any immediately following its initial release around 2013. It took several years before it became available under licence to other companies and began being offered directly by powder producers like Toyal. The most recent of these suppliers, CNPC, a rapidly growing provider from China, was announced at this year’s Formnext.

The interest that Scalmalloy generated did, however, spark many more attempts to enhance existing wrought and cast alloy compositions with these and other transition and rare earth metals. Probably the most significant advantage of this alloy was that, for the first time, it was possible to achieve higher strengths in an aluminium alloy after only a single heat treatment.

The only other alloy that emerged at a similar period was the A20X casting alloy, but this was not intended for AM. A20X was derived from the familiar A201 alloy that contained copper and silver but was known to suffer from hot tearing during solidification. Aeromet International found a way to solve this problem with the formation of TiB2 particles in the melt process during the production of the alloy feedstock. These tiny particles then go on to prevent large grain growth in a similar fashion to adding grain refiners to alloys (we’ll come back to ‘pixie dust’ later on), albeit from a different starting point. Even though there was some interest in this alloy as early as 2012, it wasn’t until 2016 that Aeromet decided to produce the A205 alloy as a powder.

As with the Al-Mg-Sc alloy, however, the whole of the AM sector did not initially have easy access to the A205 alloy powder, and so development was taken up by a select few. That said, being an existing qualified aerospace-grade material allowed easy entry to that sector. It didn’t require any further additions or alterations to the composition so, as a result, it was used in the full AM production of flight-certified parts after only a short period of process development.

Unfortunately, little is ‘on record’ about where it has been used, by whom, and in what aircraft, and it wasn’t until Aeromet International chose to divest of its patented A20X alloy to Germany’s Altana that the powder became more commercially available.

AM’s aluminium expands

Aluminium alloys are prolific and used just about everywhere. However, it only takes very small quantities of other elements to change their properties. Some, similar to steels, contain large amounts of other single elements, as in the previously mentioned Al-Si alloys. Many more alloys contain a lot of small quantities of other elements.

Aluminium’s versatility has given rise to an extraordinary range of alloys, and AM is only just starting to scratch the surface of what is available. The research carried out on the aforementioned materials has already highlighted the incredible complexity of the intermetallic phases that can form and precipitate in aluminium alloys. Some of these phases impart strength, toughness, corrosion resistance and even heat resistance to aluminium.

After the AlSi10 and AlSi7 grades, the next most popular alloys are those similar to the wrought alloy 6061. This alloy is also alloyed with both Si and Mg, but that is where the similarity ends as far as PBF-LB is concerned. Just like the 2000 and 7000 series alloys, it is known to suffer from hot cracking and porosity [4].

All is not lost for 6061, though, since suppliers such as Kymera (through its Ecka Granules business unit in Germany) have developed specific grades aimed at Binder Jetting (BJT) and other AM processes. The difference for 6061 and in all 6000 series alloys stems from the very low levels of Si. This has the effect of increasing the solidification temperature range between liquidus and solidus for the main alpha-aluminium phase, whereas the higher Si content casting alloys that sit much closer to the eutectic composition have a freezing range that is much smaller. It is this difference in the solidification ranges that is the probable cause for the hot cracking and/or tearing in the 6000 series alloys.

Perhaps one of the extraordinary facts is that relatively little work has been carried out to investigate near 6000 series alloy compositions. Custalloy from Kymera [5] is also an Al-Si-Mg alloy, with a composition (3.5% Si and 2.5% Mg) that sits between the typical ranges for 6000 series and the higher cast grades, such as F357. However, these subtle changes allow Kymera to claim better mechanical performance than the more commonly used AlSi10Mg alloy (Fig. 7).

Others have tried to adjust the composition of 6061 directly, and our sister publication, PM Review, reported in November 2023 that Japan’s Proterial had released a new variant called L61P. Since then, however, there have been no updates and nothing is known about use cases.

Besides these compositions, two other possible approaches could be investigated to try to improve crack-prone alloys. Firstly, changes to the composition with the addition of other elements to encourage faster nucleation of secondary phases or prevent significant grain boundary growth; this is essentially the route taken by Airbus with Scalmalloy. Secondly, the addition of other compounds, known as grain refiners, to accelerate the formation of metal crystals from the melt pool; several suppliers, as we are about to explore, have now introduced alloys based on the concept of pixie dust.

Whilst there has been an incredible amount of research carried out in university settings into other possible aluminium alloys based on existing wrought series alloys, very few have led to any commercialisation. For instance, the next most likely group of alloys that could be added to the AM family are the 5000 series Al-Mg alloys. These are known for their good corrosion resistance and moderate strength, making them popular in the automotive, construction, and marine industries. However, to-date there seems to be only one example of commercially available powder in the 5000 series, currently supplied by Elementum 3D.

A sprinkle of pixie dust

One can’t simply wave a magic wand over 2000 and 7000 series alloys to make them weldable and remove the risk of cracking. But we can add ‘a little something special’ to solve these problems.

It’s no secret in the world of metallurgy that grain refiners can be added to alloys to encourage fine-grained, equiaxed microstructures; they have been used in casting for decades, similar in fashion to that achieved with A20X alloys. However, when starting with metal powders, there is another approach, and one which several companies already use: blending in compounds to existing alloy powder compositions. The biggest risk to this approach is in making too big a change to the original alloy composition and, in doing so, altering the material’s properties.

First on the scene with a commercial offering was Elementum 3D with its Reactive Additive Manufacturing (RAM) technology. Realising that one size doesn’t fit all, the company developed a recipe of compounds that react with each other in the melt pool and then form sub-micron-sized particles that act as grain refiners. It’s a unique approach because, without the melting, these compounds would probably be undesirable contaminants.

The resulting fine-grained microstructures have also proven to be very strong with excellent fatigue performance. What’s more, Elementum 3D developed several aluminium alloys almost in parallel and has found that the RAM can even be used with pure aluminium powder to give it better physical properties. To date, the company has applied this technology to 1000, 2024, 5083, 6061, and 7050 (Fig. 8).

In 2019, shortly behind Elementum 3D, HRL Laboratories followed a more conventional approach when releasing its 7A77 alloy. It is worth noting that HRL were the first to respond to a change in the numbering scheme used by The Aluminum Association (AA). When HRL decided to work with the 7075 alloy and subsequently add its own pixie dust (zirconium hydride nanoparticles [6]), it registered this new grade as 7A77.50.

Recognising that taking any existing alloy and producing it as a powder meant it could not properly be identified by either the cast or wrought alloy specifications, the AA decided to introduce a new scheme for powders. The new AA scheme includes annotations for the powder form and any subsequent solid alloy form produced from the powder. In this way, the AA has provided a clear distinction between the more common wrought alloys, even though the powders may be derived from the same base alloy family. Others have since followed the new numbering scheme with 2A05.50 (the A20X alloy from Eckart) and 6A61.50 (6061-RAM2 from Elementum 3D).

The arrival of new, AM-specific alloys

So far, we’ve only looked at those alloys that have been altered in some way to make them more process-friendly, particularly for PBF-based Additive Manufacturing processes. However, there have also been some significant developments of completely new alloys targeted at metal AM. Companies such as Constellium, Fehrmann, NanoAl, and Toyal have all released alloys with completely new compositions; even machine OEM EOS has been added to the mix.

Fehrmann

Fehrmann’s aluminium alloy, AlMgty, was introduced to address the critical need for high performance in a cost-effective alloy. Now a family of alloys, it was the first to be offered with a balance of strength, flexibility, and corrosion resistance against economic cost, attempting to be a game-changer in the AM landscape. Though not designed just for AM, the journey to develop AlMgty 80 began in 2017, with patents filed a year later and the eventual launch at Formnext in 2019. This led to quick adoption in the marine sector by Ziegelmayer, the yacht builder.

Of course, where weight reduction and performance are paramount, Al-Mg alloys do find favour. Applications in the automotive and aerospace sectors to produce sliding covers and vehicle chassis parts have demonstrated weight savings as well as lead to better fuel efficiency and sustainability.

However, unlike others examining this group of alloys, the Fehrmann approach was to simplify the alloy composition, avoiding expensive transition metals or rare earth elements, to target cost efficiency for those seeking lightweight and high-strength aluminium alloy solutions. Now, after several years of development, the AlMgty range has expanded to seven versions, including a Si-free version for successful colour anodising.

Lastly, whilst not one of the biggest suppliers of aluminium alloys, the company does come from a solid background in materials development. This has allowed it to investigate other alloys, which culminated in the release of a new Al-Zn alloy, AlZnty, believed to be the first of its kind dedicated to AM. Furthermore, Fehrmann is a key member of the German state-funded SIGNAL project, seeking to develop sinter-based aluminium alloys to be used in Binder Jetting applications.

Looking ahead, the company hopes to accelerate its alloy development through its own MatGPT software tool to optimise compositions in shorter times. If the outcomes of the SIGNAL project are positive, this indeed could be the significant step forward that metal AM needs, as the market demands for increased production rates could be conceivably met by Binder Jetting, much in the same way that we have seen for Metal Injection Moulding and high-volume production.

NanoAI

Another company that also initially focused on Al-Mg, NanoAl released its Addalloy 5T in 2020, and, although based on a 5000 series alloy, it was designed to be post-processed with a simpler heat treatment step following AM fabrication. There is not much known about the alloy, as NanoAl gives away very few details, but it is known to use Zr as the main constituent imparting greater compatibility for PBF-LB processes, and this could contain greater than 1 wt.% Zr [10]. Also in 2020, the company added Addalloy 7s, based on a 7000 series alloy, and Addalloy HX, that it describes as a low-alloyed aluminium.

A 2020 issue of Metal AM reported that NanoAl, a subsidiary of Braidy Industries serving as its research and development division, won a Gold Edison Award for 3-D Printing Enhancements for its proprietary Addalloy range. However, even following this highly prestigious award and the distribution agreement signed with Mitsubishi, it is rather difficult to come across any significant uses or success stories for these alloy powders in AM.

Equispheres

Some companies may have chosen to pursue new alloys while relying on traditional methods to produce their powders. However, it is well understood that aluminium alloys have historically been difficult to atomise and make into high-quality spherical powders. This is where a company like Equispheres stands out, as it has developed a unique atomising process to produce extremely uniform powders.

PBF-LB with aluminium is accepted as a more sensitive process, with this often attributed to the variable quality of aluminium powders. Early supplies consisted of powders that were at best described as ‘rounded’ rather than genuinely spherical. By the time AlSi10Mg was first introduced, AM users were already familiar with the quality of spherical powders, such as those used for CoCr and maraging steel.

Looking beyond the morphology of aluminium powders, there has also been significant concern within the community about the safety of using aluminium powders. There was even a fear of explosions associated with aluminium, which deterred many from considering its use. Equispheres was the first to directly address these concerns with its proven, non-explosive AlSi10Mg solution, NExP-1. This safety is achieved through uniformity in size and the complete absence of fines, a unique offering in the sector to this day.

The company reports that it now produces several versions of these alloys, specific to customer requirements. One patented solution is optimised for high-volume production applications. The uniquely uniform sphericity is said to allow for higher build speeds over a wider processing window in PBF-LB manufacturing. Another precision powder line has been engineered for applications that require greater control of feature resolution and surface finish, such as RF components.

Over the past few years, the company has been very successful at attracting investment, which most recently has enabled Equispheres to increase production capacity. In 2024, following the installation of new atomising reactors, the company reported an order increase of 300%, with a commitment to supply the majority to existing customers.

Toyal

A company that is certainly no stranger to producing aluminium alloy powders is Toyal, already having a number of the so-called ‘standard’ alloys familiar to the AM market in its portfolio. However, perhaps less well-known is that the company has introduced a few other alloys for use in Additive Manufacturing under its Spheralloy brand. Along with the high Si content alloys, AlSi10 and AlSi12, other casting alloys Si9Cu3 (LM26), AC8A (LM13), and ADC12 (LM2) all list Cu and Fe as significant additions, presumably for enhanced precipitation hardening.

Toyal has also developed its own alloy, TCFE1Z, targeted at lightweight heat exchangers for the automotive sector and air conditioning units. Classed as a low-alloy aluminium, it has just 1.2% Fe and not much else. Its apparently unique feature as an AM material is higher corrosion resistance compared to AlSi10Mg and other commercially available alloys.

Constellium

Constellium’s Aheadd alloys were also developed to address the growing demand for high-performance materials in Laser Beam Powder Bed Fusion (PBF-LB). The company involved industry partners during its extensive research and collaborated closely with a number of machine OEMs to develop alloys offering high strength, thermal stability, and good corrosion resistance. The launch in 2020 included two main variants: Aheadd CP1, which is purported to be optimised for high conductivity and productivity, and Aheadd HT1, said to be designed for high-temperature and high-strength applications.

Constellium has perhaps been a little less shy than some others about announcing which customers have used the Aheadd alloys. One notable example is the production of braille handrail signs for Deutsche Bahn, Germany’s national railway company. These signs, made using CP1, are designed to assist visually-impaired passengers by providing tactile information in braille. And while AM is no stranger to F1, the use of aluminium is still uncommon, making it noteworthy that PWR has been using CP1 alloy for heat exchangers.

EOS

In a rather unique position, as the only machine OEM with a team dedicated to the development of the powder supply chain incorporating the innovation of new materials, EOS has released two high-strength aluminium alloys. This has come as a response to demands from existing customers for higher strength, higher temperature capabilities, and the ability to be anodised or electrolytically polished.

As a nod to the growing concerns about the costs of AM parts (even if, in many cases, the idea that AM is more expensive than traditional manufacturing is incorrect), EOS acknowledged that any new alloys also had to come with a completely different cost structure, targeting more economical overall costs when compared to existing custom high-strength AM aluminium alloys already in the market.

EOS released the recognised aluminium alloy, Al2139 AM, for elevated temperature use. The company claims that this has unmatched strength in the range of 50-200°C. Additionally, EOS has recently developed a new alloy, Al5X1, which combines high ductility, moderate strength, and higher corrosion resistance with an ability to be colour-anodised. Speaking to its development team at Formnext, they were keen to point out a small bracket component under evaluation at a leading automotive company, shown here in a striking anodised red finish (Fig. 11).

It’s also clear that applications such as this will keep the use of aluminium in AM on the increase, and, for once, it is perhaps a good thing that it is not solely dependent on the aerospace sector. One reason behind EOS’s decision to develop its own alloys was to address the costs of purchasing and post-processing high-strength aluminium powders. For instance, the Al-Mg alloy, Al5X1, has the benefit of not requiring water quench prior to ageing and has significantly higher yield and tensile strength than AlSi10Mg. Additionally, neither this nor the Al2139 alloy contains expensive elemental additions.

It would be remiss not to mention the work EOS has done to highlight sustainability. Last year, it was reported that 2024 would see EOS demanding its AlSi10Mg suppliers to use at least 30% recycled alloy feedstocks, targeting a 25% reduction in CO₂ emissions. Most other powder producers rely on the provision of green energy, and, whilst it is generally accepted for other metals such as steel, the use of recycled aluminium has always been a source of concern. Even though EOS does not directly produce its own powders, it is certainly a step in the right direction to use recycled materials, and the response from existing customers has been reported to be positive. In fact, so much so, that EOS is now seeking to increase the percentage of recycled feedstock in its aluminium powders.

New processing technologies broaden the potential of aluminium AM

While PBF-LB has dominated for many years and Directed Energy Deposition, whether using lasers or arc welding technologies, has started to gain more ground, in some ways, both may have been a hindrance to the wider adoption of metal AM. This is down to the fact that most of the AM world has been focused on chasing the high-value opportunities associated with working with titanium, nickel superalloys, or other special steels and alloys. The lack of choice and difficulties of having to deal with the interaction between highly reflective materials and lasers combined with complex heat treatment cycles may also have deterred others from wanting to work with aluminium alloys.

Developing better alloys, those suited directly to fusion-based AM technologies [8], is one route to working with aluminium. The other is changing the technology. This is why we have seen the recent emergence of several alternatives to PBF-LB, some of which are inherently more appropriate for aluminium or other metals with relatively low melting points.

Some of the best solutions are relatively simple. For new aluminium-based AM technologies, success has not always come from groundbreaking inventions but from innovation. Innovation enables the repurposing of existing technologies into AM applications. These include Binder Jetting and Cold Spray and – to a lesser extent – Directed Energy Deposition.

While aluminium was not an early focus of these technologies, this has shifted – something especially evident after visiting Formnext this year. It’s worth noting two new DED technologies, as both companies chose to launch with aluminium wires rather than the more common materials.

Caracol, already known for its large-format robotic FDM machine for polymers, introduced a new DED machine this year. The Vipra machine incorporates two welding technologies, one of which uses Cold Metal Transfer, a form of MIG welding where the weld wire sequentially withdraws from the weld pool before ejecting a drop of metal. This cooler process is ideal for aluminium alloys, such as the 2319 alloy highlighted at the exhibition.

Another new player in the AM scene is MADDE from Korea. While its DED process is similar to others on the market, the company launched by demonstrating its capability to additively manufacture virtually any aluminium alloy available in wire form. Speaking with one of the founders, it was stated that the process had already been optimised to work with 5000 series alloys and that they plan to release parameters for 2000, 6000, and 7000 series aluminium alloys in 2025.

Leaving behind the more common technologies for a moment, new adaptations of existing technologies have been developed specifically to exploit aluminium’s low melting point. These include Ultrasonic Welding (UAM), Friction Stir Welding (FSW), Liquid Metal Jetting (LMJ), and a form of Fused Filament Fabrication (FFF), along with variants or combinations of these technologies, collectively referred to as Molten Metal Deposition.

Ultrasonic Additive Manufacturing

Ultrasonic AM has most notably been developed by Fabrisonic. The technology deposits strips of metal, similar to Laminated Object Manufacturing (LOM), and has already been successfully applied to aluminium alloys. However, Fabrisonic did not set out to solve AM just for aluminium; in fact, the main string in the technology’s bow is that it allows for the deposition of different metals that are traditionally difficult to join. It is also commonly used in hybrid applications, where CNC machining is combined with depositions, as well as for embedding electronics and sensors into metal parts.

It appears that Fabrisonic is the sole vendor offering this specific type of technology. However, I am convinced I have come across at least one other form of UAM developed for aluminium wire or rods. Unfortunately, the quirks of internet search engines and my fading memory have kept me from locating more information. I will leave that as a challenge for readers to explore further.

Before we leave UAM, it is also worth noting that ultrasonics have been combined with a number of other metal AM technologies, such as DED and PBF-LB, in order to control microstructures forming out of the melt. Whilst research in this area has not primarily been for aluminium alloys, in aiming to solve some of the difficulties of trying to work with other metals that are prone to cracking, this could likely be applied to the non-weldable, high-strength aluminium alloys.

Additive Friction Stir Deposition (AFSD)

Adapted from the friction stir welding solid-state joining process, AFSD uses a non-consumable rotating tool to generate frictional heat and plastic deformation in a consumable alloy rod. It is effective for use with any of the common aluminium alloys, including those in the 2000, 5000, 6000 and 7000 series of alloys. The most important aspect of AFSD is that there is no melting, even though the temperature can be near the melting point. This means there is no risk of solidification cracking, even when relatively large volumes are being deposited. In fact, this last point is also one of AFSD’s other advantages, as large parts can be produced in a relatively short time. Secondly, since there is no melting, AFSD also avoids the risks associated with void-free, fully dense parts and can result in refined microstructures, improving strength and fatigue resistance.

AFSD has been successfully applied to various aluminium alloys, including high-strength grades like 7075. However, unlike most AM applications which are focused on manufacturing new components, AFSD has often been studied for use in repair. This was the subject of several talks this year at the AMUG conference in Chicago, where Boeing presented several use cases. In Boeing’s view, AFSD is particularly valuable for maintaining and repairing critical aerospace components where material performance and reliability are paramount.

In terms of equipment suppliers, MELD Manufacturing Corporation is one of the leading providers of AFSD technology within the AM sector. There have been many adaptations of existing FSW machines for use in AM, particularly within institutions such as the TWI in the UK and EWI in the USA. One would anticipate seeing several other suppliers in the coming years since AFSD is also particularly suited to large-scale AM and hybrid systems that are combined with CNC machining.

Liquid Metal Jetting (LMJ)

This process involves the controlled ejection of molten metal droplets to build up a part; to date, it has only been successful with aluminium alloys. It works by passing aluminium wires through heating coils, melting the alloys into a crucible, and agitation of this crucible results in the controlled expulsion of a droplet of molten alloy. The drops deposit and solidify to form the object.

LMJ’s journey began with Vader Systems, a startup founded by Scott and Zachary Vader, the inventors of MagnetoJet. This attracted quite a bit of industry interest right from the start since the concept, in essence, seemed rather simple and similar to inkjet printing. To underscore this fact, in 2019, Xerox – very well known in the inkjet space – acquired Vader Systems to enhance its own Additive Manufacturing capabilities.

Under Xerox, the technology was developed further and the company rebranded as ElemX. However, even though it had successfully signed agreements with the US Navy, the Rochester Institute of Technology and Siemens, the company failed to realise significant commercial success. The ElemX business was then acquired by Additec in the summer of 2023 (Fig. 13).

The journey for LMJ continues with the newest entrant, GROB, making a significant impact on this year’s Formnext exhibition. Although there was no live operating machine at the show, it was clear that it is aimed towards an integrated hybrid AM machine architecture.

Stack Forging

Alloy Enterprises has come up with a unique way to make parts in 6061 from rolled sheets. This new method is probably the most like LOM in that it uses laser-cut profiles that are stacked together to make 3D parts. Simply, the machine removes all the holes that make hollow volumes within solid parts of each layer, then coats the surface with an inhibitor that acts like a mould-release agent. Once all the cut sheets are precisely stacked, they are ‘forged’ together by diffusion bonding, resulting in a semi-solid block.

The 3D object can rest securely in the block since it is encapsulated in the non-bonded support material. Once the support material, previously treated with the inhibitor, is removed, the parts need a further heat treatment for the desired strength or other properties.

So far, the process has only been applied to 6061, but it would be easy to imagine other aluminium alloys being used in this new form of metal AM.

FFF for metals

Metal Fused Filament Fabrication (FFF) has been successfully applied to metals by mixing metal powder with polymer compounds, and commercial solutions have been available for several years. However, processing aluminium via sinter-based routes presents known challenges, meaning very few have attempted it. One company, however, has successfully overcome this difficulty, but with a twist on FFF: by directly depositing fused wire without the need for any polymer binder.

Valcun, the Belgian-based inventors of the Minerva technology, have achieved this innovation, which they call Molten Metal Deposition (MMD). Valcun has kept things relatively simple with a machine that can be plugged into any domestic electrical supply, much like the numerous FFF-style plastic printers operating in the Free Form Fabrication space.

Though it currently only offers 4008 and 4043 as standard weld wires, Valcun states that 6061, 6082 and 7000 series alloys will also be available soon. However, other aluminium weld wires could probably be used in this technology (e.g. the A20X alloy from Eckhart in Germany, and the wires from Fortius Metals produced using Elementum3D alloys).

The MMD process has also been used to produce parts that require no further post-processing: not just aesthetically pleasing lampshades but real-world engineering components. At the recent Formnext exhibition, Valcun showcased a cooling fan used in data centres that was 10% more efficient than the previously manufactured part. Each of the fins was in the as-built condition, and it was suggested that the surface roughness had no negative impact on the aerodynamics, possibly because the layers are parallel to the flow of air in this application.

Aluminium’s future

Looking ahead, we should expect to see much more growth in the use of aluminium for Additive Manufacturing applications. Over the past decade, it’s been shown that it isn’t so simple to turn profits from low-volume, high-value items produced from expensive alloys; this is one area where growth could certainly be driven by the adoption of aluminium.

At Formnext this year, the presence of AM service providers was somewhat limited, so it wasn’t possible to test this hypothesis in great detail. However, at least one specialist in this area was present: Conflux Technology.

Conflux has become an expert in producing incredibly fine structures in aluminium alloys using PBF-LB for heat exchangers, so we asked for their opinion on the subject. Like much of the broader industrial sector, those working within the company would like to see aluminium alloys better-suited to the harsh applications that currently require higher-performing wrought alloys. For example, with parts now in production for the AMCM machines (Fig. 15), Conflux can build heat exchanger geometries that outperform their traditionally manufactured counterparts.

To maintain its advantage, however, the AM parts must match or exceed the mechanical, thermal, and corrosion-resistant properties of their traditionally made equivalents. As such, Conflux is encouraged by the market’s movement toward new high-performance aluminium alloy powders for application development. Still, the company would like to see more focus on the impacts of the build process on final properties, particularly in addressing anisotropy and achieving ageing during the AM process, so as to avoid the need for secondary heat treatments.

Conclusion

We have shown that there are now many more alloys available, opening up the potential for a broader range of applications. This article hasn’t even attempted to include all of the powder producers, of which there is an ever-growing population. Considering this, it becomes clear that now is the time for the industry to remember that aluminium alloys have historically been developed with specific properties that provide clear advantages for particular applications. As far as AM is concerned, this specificity is exactly what we need more of; nothing demonstrates this more clearly than the extensive range of wrought aluminium grades.

The AM sector and the supply chain it supports do not need to compete for applications that have always been better-suited to other alloys; aluminium’s lightness already supports a strong business case, and Additive Manufacturing offers highly viable solutions for processing it. Instead, the sector should place its focus on developing Al alloys for use in places where they best serve and are specifically suited to the unique requirements of Additive Manufacturing.

Author

Dr Martin McMahon
Technical Consultant, Metal AM magazine, and founder of M A M Solutions.
[email protected]

The author expresses his sincere gratitude to all companies who shared insight for this article, and in particular to Conflux Technology, Continuum Powders, Eckart, EOS GmbH, Equispheres, Fehrmann Materials, MADDE and Valcun for their contributions.

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