U.S. tariffs on imports of steel and aluminum are a jolt to the supply chains for those materials, instantly putting buyers of raw and semi-finished metals, as well as components like castings, on notice. The situation in the aluminum sector is especially interesting, because despite the rising importance of aluminum alloys for lightweight design the domestic primary aluminum industry has not grown or expanded.
That means demand for more aluminum alloys will be focused on the secondary market – and researchers are getting ready. A study published by the U.S. Dept. of Energy’s Pacific Northwest National Laboratory indicates that aluminum scrap from industrial waste streams can produce high-performance metal alloys. The aluminum performs comparably with identical materials produced from primary aluminum, indicating that this solid phase alloying process may be a low-cost route for bringing high-quality recycled metal products to the market.
The researchers emphasize the environmental impact as well as the industrial advantages. "The novelty of our work here is that by adding a precise amount of metal elements into the mix with aluminum chips as a precursor, you can actually transform it from a low-cost waste to a high-cost product,” wrote Xiao Li, a PNNL materials scientist and lead author of the research study. “We do this in just a single step, where everything is alloyed in five minutes or less."
The solid-phase alloying process converts aluminum scrap blended with copper, zinc and magnesium into a precisely designed high-strength aluminum alloy product, again, in just a few minutes, compared to days required to produce a similar outcome through conventional melting, casting and extrusion.
The research team used a Pacific Northwest National Lab-patented technique called Shear Assisted Processing and Extrusion, or ShAPE, to achieve their results – but they note that the findings should be reproducible with other solid-phase manufacturing processes. In the ShAPE process, high-speed rotating dies create friction and heat that disperses the coarse starting ingredients into a uniform alloy with the same characteristics as a newly manufactured aluminum cast or formed product. There is no energy-intensive bulk melting, which is another cost-cutting factor.
The researchers used both mechanical testing and advanced imagery to examine the internal structure of the upcycled materials they produced by solid phase alloying. Their results showed that the ShAPE alloy imparts a singular nanostructure at the atomic level, called Guinier-Preston zones, which improve mechanical strength in metal alloys. Compared to conventional recycled aluminum, the upcycled alloy is 200 percent stronger and has increased ultimate tensile strength. These characteristics could translate into longer-lasting and better-performing products.
Manufacturers sourcing higher-performance metals may also benefit from research reported by the DOE’s Ames National Laboratory in Iowa, involving high-temperature superalloys.
Jet engines generate a lot of power and a lot of heat, so the materials used to form these systems and their component parts environments are typically nickel- or cobalt-based alloys, called superalloys, which can tolerate temperatures around 1000°C (or 1832°F).
Researchers there have discovered a new alloy that can replace nickel- and cobalt-based superalloys in gas turbines for both aviation and power generation. They used a computational framework to predict metal phase stability, strength, and ductility based on the types of atoms involved. The framework can very quickly test thousands of material combinations.
Manufacturers sourcing higher-performance metals may also benefit from research reported by the DOE’s Ames National Laboratory in Iowa, involving high-temperature superalloys.
Jet engines generate a lot of power and a lot of heat, so the materials used to form these systems and their component parts environments are typically nickel- or cobalt-based alloys, called superalloys, which can tolerate temperatures around 1000°C (or 1832°F).
Researchers there have discovered a new alloy that can replace nickel- and cobalt-based superalloys in gas turbines for both aviation and power generation. They used a computational framework to predict metal phase stability, strength, and ductility based on the types of atoms involved. The framework can very quickly test thousands of material combinations.
Ames’ lead research scientist Nicholas Argibay noted that gas turbines are more efficient when they operate at higher temperatures, around 1400°C (or 2552°F). Given these high operating temperatures, the heat tolerance limits of nickel- and cobalt-based superalloys have been a limiting factor in improving energy efficiency.
"We currently use cooling and other tricks to try to make those engines run very hot, but ultimately we are limited by the melting temperature of those materials,” according to Argibay. “There are about nine elements that melt at much higher temperatures than nickel and cobalt, and those are called refractory metals. The reason we don't use those metals now is because they're brittle at low temperatures they're hard to manufacture and shape into parts."
A solution to the challenges posed by refractory metals is to combine them into multi-principal-element alloys. Multi-element alloys are not based on one metal that holds everything together, like a nickel- or cobalt-based alloy. Instead, multi-element alloys consist of three or more elements, none of which exceeds 50% of the overall composition.
The researcher added that combining many of these otherwise brittle pure elements in significant amounts creates atomic structures that he described as "emergent, unique, properties."
Determining the materials and the appropriate amounts of each was done using the computational framework developed at Ames Lab by two more research collaborators, Prashant Singh and Duane Johnson.
Singh explained that mixing more than three elements results in millions of combinations to search for, which Johnson noted they addressed using a “theory-guided methodology that interfaces with experiments,” and points them toward new alloys with the specific properties that they want in materials."
This new multi-element alloy is more resilient to deformation at higher temperatures than the alloys currently in use, which means that the material can be exposed to much hotter temperatures and eliminates the need for cooling the engine which causes energy loss.
Thanks to its composition, this alloy also has the necessary ductility to make it suitable for manufacturing using commercially established methods.