Lightweighting has been and continues to be a major concern for the aerospace, automotive, and transportation industries. Whether it’s an airplane, automobile, boat, or train, the use of lightweight materials, such as aluminum, provide significant fuel savings and performance benefits. Like its competitors in the lightweighting arena (steel, composites, etc.), aluminum is working to continually improve its strength-to-weight ratio, structural performance, and mechanical characteristics through the development of new alloys and manufacturing processes. Recent developments in nanotechnology may further support aluminum in this pursuit.
MetaLi LLC, an innovative new company headquartered in Los Angeles, CA, is working to further improve the physical and mechanical behaviors of light metals through the implementation of nanotechnology. Recently, the company provided a leap forward in light metals engineering, introducing new welding wires comprised of 7000 and 2000 series alloys that were previously thought to be unweldable. This development has the potential to lead to advances in the aerospace industry, as well as allow widespread use of 7000 series high-strength aluminum alloys in mass-produced applications like cars.
Prof. Xiaochun Li (Figure 1), the founder and chief scientist of MetaLi and a professor of Materials Science and Engineering at UCLA, coined the term “nanotech metallurgy,” which focuses on how nanophases can be engineered and applied to metals for improved performance. He believes that nanotech metallurgy has the potential to revolutionize metals processing and manufacturing, ultimately benefiting the aerospace, automotive, and other industries.
Li has been researching the effects of nanoparticles on solidification and manufacturing of light metals since 2002. Nanotechnology is the science and engineering of particles conducted at the nanoscale (about 1 to 100 nanometers, with 1 nanometer being one billionth of a meter). When applied to other materials (such as aluminum and other light metals), nanotechnology has the potential to provide a number of significant advantages, including increased strength, improved formability, and a resistance to hot cracking.
“I was focused on chasing ‘big ideas’ of mass production (especially casting) of light metals using nanotechnology,” said Li. “I also had the problem of finding a way to achieve scalable nanoparticle dispersion and stabilization in molten metals, which is essential for large scale production of metals containing nanoparticles.”
Li and his team went through several rounds of research trying to solve the dispersion problem, starting with mechanical mixing of the nanoparticles and moving to ultrasonic processing. Neither provided the level of dispersion at the volumes required.
In 2015, the researchers achieved a breakthrough while studying SiC nanoparticle clusters in a magnesium sample. Instead of being fused together, as expected, the nanoparticles were separated by metal at the nanoscale. As Li and his team grew to understand the physics behind this phenomena, they discovered a new mechanism of nanoparticle self-dispersion in molten metals, such as aluminum, magnesium, and copper, etc. This discovery enables the scalable production of nanotechnology-enhanced light metals using standard, inexpensive casting methods.
MetaLi LLC was founded by Li in 2016 to commercialize the new nanotechnology-enabled metal products. When considering which opportunities to pursue, the company began to consider the hot cracking problem in 7000 and 2000 series aluminum alloys as an easy penetration pathway for industrial applications. Due to their high strength, 7000 and 2000 series alloys are often used in aerospace and military applications. In particular, AA7075 (Al-Zn-Mg-Cu) is used as a fuselage material in aircraft, as it is one of the strongest aluminum alloys available. However, due to the way it solidifies, the alloy is notoriously susceptible to hot cracking during traditional fusion welding, forcing aircraft manufacturers to primarily use riveting in the joining of its high performance structures.
“We noticed that use of the highly coveted AA7075 for fusion welding (e.g., arc welding) was largely considered impossible, which significantly limited its widespread use,” said Li. “We decided to solve this problem as a showcase for the newly developed nanotechnology methodology for metallurgy.”
One of the key steps in addressing this challenge was finding suitable nanoparticles that would provide grain refinement for the primary phase, as well as functioning well during the secondary phase of solidification. After two years of research, MetaLi was able to implement titanium carbide nanoparticles in AA7075 welding wire, producing welded joints with a tensile strength of 392 MPa without cracking (Figure 2). With post-welding heat treatments, the company was also able to produce joints that could achieve 551 MPa.
The company began producing and selling nanotechnology-enhanced 7075 and 2024 alloy welding wires in 2019—working closely with manufacturing partners in the U.S. and overseas to produce the welding wire with a current capacity of 500 tons per year. The company is planning to register its alloys with the Aluminum Association and the American Welding Society in the future.
One of the benefits of nanotechnology is that it can be seamlessly adopted to traditional manufacturing routes, improving the final products without having to change production facilities. “Of course our proprietary nanoparticle incorporation and dispersion technology would require some melting, synthesis, and dispersion equipment, which is readily available in the market,” said Li. “The key of course is in the know-how.”
With the hot cracking resistance afforded by nanotechnology, MetaLi has been able to follow up by applying the technology to additive manufacturing. The company’s welding wire has been used in wire arc additive manufacturing to produce 7075 and 2024 components. Nanoparticle-enriched 7000, 2000, and 6000 series aluminum alloy powders have also been produced for powder-based additive manufacturing for the commercial market.
“Additive manufacturing is a very rich direction for our nanotech-enriched powders and wires to deliver unprecedented properties for widespread applications,” explained Li. Other light metal products being produced by MetaLi include high strength super aluminum, high temperature resistant aluminum, self lubricating aluminum, high strength super copper, high strength super magnesium, and more. “We already have more than 40 customers worldwide for our products,” noted Li. “We are consulting with industry professionals and discovering new market areas every day. It is exciting to see how much we can do with nanotech metallurgy.”
A New Age of Metallurgy
Nanotech metallurgy is creating new and exciting manufacturing opportunities, while pushing the performance envelope of aluminum alloys to meet energy and sustainability challenges in human society. High-performance nano-treated aluminum alloys made possible by MetaLi provide superior strength, weldability, processability, and corrosion resistance while maintaining light weight—further anchoring aluminum as an ideal material for the aerospace, automotive, and transportation industries.
Although aluminum is a key focus for the company, Li pointed out that nanotech metallurgy has the potential to be groundbreaking across the materials spectrum. “We consider ourselves a pioneer and a global leader in the new age of nanotechnology-enabled metallurgy for light metals,” stated Li. “We are on a path to break the traditional metallurgical barriers, providing innovative and competitive solutions in new materials. Together with our customers, we will revolutionize the traditional metal manufacturing industry.”