Aluminium matrix composites (AMCs) first emerged around 40 years ago for use in automotive components and now, thanks to a myriad of applications showcasing their capabilities and highlighting their sustainable appeal, it looks as though they are beginning to attract increasing interest from manufacturers and engineers looking for a viable alternative to existing materials.
Back in the 1980s, when AMCs first appeared, their advantages were often over-sold and their properties were largely unproven, cutting short their potential and doing little for their reputation. As carbon composites became more widely adopted, AMCs were soon forgotten by manufacturers and engineers, and promptly fell off the radar. However, almost four decades later subsequent R&D investment into the manufacturing of these composites has resulted in progress that has been deemed a bit of a market changer. Sectors such as automotive and aerospace are under sustained pressure to improve performance, and with weight reduction playing a key role, AMCs are no longer bottom of the heap, fast becoming the ‘new’ solution to address legislation and other growing industry demands.
One pioneer of AMCs is UK firm Alvant. Originally formed in 2003 as CMT, Alvant has created a process known as advanced liquid pressure forming (ALPF), a method by which the company brings together aluminium, which acts as the matrix, and a high strength reinforcement fibre to create a high-performance aluminium matrix composite material. There are four Alvant AMC materials families, namely AlXal (pronounced Al-Zal) – a continuous fibre reinforced AMC; ParXal – a particle loaded AMC; AerXal – an aluminium syntactic foam and CorXal – a unique high-performance multi-phase AMC similar in concept to a sandwich material. Traditional sandwich materials are typically assembled from carbon composite or unreinforced metallic panes with a variety of honeycomb cores. The metallic pane sandwiches are typically flat, 2D panels, while carbon composite varieties can take 3D forms. Alvant’s adoption of a single-shot manufacturing process for its CorXal product offers ultra-high stiffness and low density (~1.9g/cc).
High strength, high performance AMCs
Compared to unreinforced metals, AMCs also have lower weight and superior wear resistance, as well as special thermal and electrical properties, making them ideal for use in the engineering of durable lightweight components for harsh environments. They also offer multiple advantages over polymer fibre reinforced materials, such as carbon composites. These include higher transverse strength and stiffness, a higher thermal operating range, better wear resistance, superior damage tolerance and easier repairability.
In fact, Alvant believes AMCs can have superior strength compared to steel at less than half the weight. This means highly loaded components made from traditional metals, such as steel, titanium and aluminium can be replaced by lightweight, low inertia parts without any increase in package size.
To manage cost and complexity, components are not necessarily manufactured entirely from aluminium matrix composite; for example, if they have regions of low stress where enhanced mechanical properties are not required. In such cases, components can be reinforced locally in a method known as hybrid-AMC. In these applications, performance is provided precisely where it’s needed by using AMC inserts applied to the larger aluminium component. This limits the fibre content, simplifies the AMC insert geometry and reduces costs whilst increasing the performance and capability of the component.
The production-readiness of AMCs is also proving timely. With increasing commercial demand for strong but lighter parts across automotive, aerospace and marine sectors, manufacturers are looking for ways to increase product capabilities and performance, while at the same time meeting ambitious goals for fuel efficiency and sustainability. They are also proving their capabilities especially where safety and reliability are essential, with potential use applications in high-pressure seals, safety landing gear and seats. Where performance, efficiency and precision are vital, other use cases include robotics, electric motors and automotive suspensions. And because AMCs are capable of withstanding elevated temperatures (~300ºC), they are suitable for components in high-voltage battery systems, unmanned aerial vehicles that fly at high altitudes and vehicle powertrains.
The growing awareness among product manufacturers and the industry at large of how AMCs can sometimes be a better alternative than other composite materials or unreinforced metals is evident, by the calibre of partners across aerospace and automotive sectors signing up to new projects with Alvant, as well as by big-brand collaborative projects and UK government funding.
In recent years, aerospace companies Rolls-Royce and Safran Landing Systems, and car maker Ford, have all engaged in collaborative projects with Alvant, illustrating the industry sectors lining up as early adopters of AMCs.
In May 2018 the company concluded a three-year, £1.2m R&D programme it led with a grant of £412,000 awarded under the ‘Make it lighter, with less’ competition run by Innovate UK. Collaborating with industry world-leader GE Aviation, electric motors and controllers producer YASA Motors, and the National Composites Centre, this project created new computer aided engineering (CAE) software modelling packages for the design and analysis of AMCs to reduce product development lead times.
The project achieved a 40% rotor weight saving on an axial flux electric motor, such as that used in electric cars, while increasing the rotor’s power-to-inertia ratio potential. In addition, the number of assembly line parts was reduced to shorten the assembly time.
According to Alvant, as electrification increases, vehicle manufacturers are seeking to optimise motor efficiency maps; for example, by improving the efficiency as a function of torque and speed that ultimately determines the energy consumption for vehicles. The industry faces the challenge of identifying ways to improve efficiency and performance, whilst simplifying manufacturing and overall cost.
“Using AMCs, we have been able to reduce the weight yet retain the stiffness and strength of the electric rotor, to minimise parasitic mass and produce a better power-to-weight ratio of the entire motor, therefore improving efficiency, range and responsiveness,” says Richard Thompson, commercial director of Alvant. “In addition, we can also offer better thermal resistance, up to 300°C, making AMCs a more suitable material than polymer composites for applications such as motors, batteries, energy recovery systems, fans and flywheels.”
Alvant has also been participating in a two-year, £28m project titled ‘Large landing gear of the future’ at the invitation of project-leader Safran Landing Systems.
Current landing gear systems are typically stronger and heavier than necessary because an outstanding safety record has resulted in proven techniques being perpetuated. However, they account for approximately 3% of aircraft weight, with a corresponding effect on fuel consumption.
“The project aims to make use of new materials and manufacturing methods to develop and demonstrate technologies that will reduce landing gear weight, fuel burn and noise at the same time as improving reliability and lowering maintenance, repair and operating costs,” adds Thompson.
Alvant’s contribution to the project is the design, manufacture and testing of an AMC brake rod, targeting a 30% weight reduction over an equivalent titanium component whilst maintaining the same strength as steel.
“A key objective of the Large Landing Gear project is to test and demonstrate as many technology advances as possible,” continues Thompson. “Alvant’s supply of components for fatigue and stress testing to an aerospace tier one suppliers signifies a major step forward in proving the reliability and airworthiness of our unique materials.”
With BA, Virgin Atlantic and Qantas all scrapping their Boeing 747 fleets earlier than scheduled in light of the coronavirus downturn last year, Alvant strongly believes this opens up significant opportunity and creates the urgent need for the industry to think and act differently as we head into the future, by investing in sustainable materials for new, more fuel-efficient aircraft to help achieve net-zero carbon emissions by 2050.
Alvant is also currently looking at exploring further potential aerospace and defence applications of its CorXal material, with one example including the incorporation of a single piece AMC in the leading edge of aircraft wings.
Aircraft wings are subject to large aerodynamic forces, huge changes in temperature and are susceptible to bird and lightning strikes. The existing materials used in traditional wing manufacture have been found to be susceptible to bond degradation between the skin and core elements. This can be caused by environmental factors such as temperature, moisture ingress, and contamination, which can negatively impact on the integrity of the bond. The result has been a tendency to design components with excessive safety factors to compensate for this potential degradation.
AMCs are driving environmental change
Arguably of most significance are the sustainable properties of AMCs, thanks to the ability to separate the fibres from the aluminium at the end-of-life stage. Manufacturers must increasingly factor whole life cost into design and it’s an area where AMCs score well. Nowadays, certain disadvantages with materials such as carbon composites and polymer composites are becoming better understood. The essence of what sustainability is has now changed scope, evolving from solely focusing on the sustainable materials to also taking into account the entire product life cycle, and the ability to reuse, which is now very much a consideration in design development.
Then, of course, there is the pandemic. The world is very different to the one that existed little over a year ago, with Covid-19 serving to redefine what sustainability actually is. Stakeholders have different expectations of businesses now, placing non-sustainable materials under far more scrutiny, and driving the trend for sustainability in manufacturing.
However, there is an even bigger picture with a significant call to action that demands immediate attention. It is abundantly clear that the planet is under threat from the irreversible effects of climate change. The biggest challenge is not just trying to rectify this, but also fighting misconceptions by many manufacturing organisations that sustainability is arduous and difficult to achieve and, more importantly, that it’s expensive and damaging to profits. AMCs are just one example of innovative materials that go a long way to prove that manufacturing can not only be carried out in a more sustainable way, but also in a cheaper way, as sustainability drives efficiency. Fundamentally, it’s about using materials that optimise energy use in the production process and reduce waste, which in turn save on costs.
The manufacturing industry is one of the biggest culprits of climate change, and if newer and more sustainable processes can now be fully embraced, it can only set the UK on the right path in becoming the leading global hub for technical innovation and sustainability.