In a paper published in the Journal of Manufacturing Processes, researchers at Pacific Northwest National Laboratory (PNNL) report that their novel Shear Assisted Processing and Extrusion (ShAPE) technology (earlier post) can extrude aluminum alloy 7075 tubing at speeds up to 12.2 m/min without surface tearing. This is first experimental evidence for high-speed extrusion of 7075, which improves upon conventional extrusion where 2.0 m/min is the limit.
Although automakers have been increasing their use of aluminum in high-volume models to reduce vehicle weight—notably Ford, which began building the F-150 with mostly aluminum bodies in 2014—even more weight could be saved by using more advanced aluminum alloys for components such as roof rails, cross beams, subframes, and other structural parts. However, these alloys are expensive due, in part, to their slow manufacturing rates using conventional extrusion.
The aluminum alloy 7075 has a strength-to-weight ratio 85% higher than the alloys found in typical passenger vehicles; however, manufacturing costs are about 30% higher compared to the 6000 series alloys that are commonly used.
That price differential is acceptable in aerospace applications, where lighter weight materials trump higher costs in order to achieve better fuel efficiency, improved maneuverability, and lower launch cost. But in vehicles, it’s a limiting factor that we hope to change.—Scott Whalen, lead and corresponding author
This high cost is primarily due to alloy 7075 being notoriously hard to extrude into structural components. 7075 is widely regarded as the most difficult to extrude of all commercial aluminum alloys. The slow extrusion speed of just 1 to 2 meters per minute, combined with higher energy requirements, make 7075 more expensive than the 6000 series alloys, which are extruded at more than 20 meters (65 feet) per minute.
PNNL’s ShAPE process uses a machine to spin billets or chunks of bulk metal alloy, creating just enough heat through friction to soften the material so it can be easily extruded through a die to form tubes, rods, and channels. The simultaneous linear and rotational forces use only 10% of the force typically needed to push the material through the die in conventional processes.
This significant reduction in force enables substantially smaller production machinery, thus lowering capital expenditures and operations costs. Energy consumption is similarly low. The amount of electricity used to make a 1-foot length of 2-inch diameter tubing is about the same as it takes to run a residential kitchen oven for just 60 seconds.
Whelan et al.
The process yields a material with microstructure grains much finer than the material’s grains before extrusion. These tinier grains and their orientation are typically uniform throughout the product, providing greater strength and ductility. For example, room temperature ductility above 25% has been independently measured, which is a large improvement compared to typical extrusions. Initial research shows that the process greatly improves the energy absorption of the metal as well.
ShAPE can extrude tubes, wire, and bars with strength properties that meet important industrial ASTM standards and ASM typical values. The elongation of alloy 7075 is 50% higher than that of conventional extrusion, which can help with energy absorption during a crash.
In addition to increasing speed, the ShAPE process can also eliminate the need for energy-intensive thermal treatment steps that are required in conventional extrusion, saving approximately 50% of the energy required for extrusion of alloy 7075.
With conventional extrusion, the large billets of metal must first be heat-treated at temperatures of more than 400 °C (750 °F) for roughly a day to homogenize, or evenly distribute, different elements such as magnesium and copper throughout the alloy. ShAPE is capable of extruding billets without homogenization, saving an estimated 5% on the total cost of ShAPE-extruded products.
Additionally, in conventional extrusion, preheating in a furnace is required to soften the billet prior to extrusion. With ShAPE, preheating is not required, since all the necessary heat comes from the process itself. Other post-extrusion thermal treatments are also eliminated or reduced, leading to the overall 50% in energy savings.
ShAPE’s increased extrusion speed, combined with reduced energy use and, therefore, lower carbon emissions, can make the lightweight 7075 alloy cost-effective for the passenger vehicle market. Lighter vehicles also ultimately contribute to reduced carbon emissions for the transportation sector through increased fuel efficiency for cars powered by internal combustion engines and longer driving distances per charge for electric cars.
Scott Whalen, Matthew Olszta, Md. Reza-E-Rabby, Timothy Roosendaal, Tianhao Wang, Darrell Herling, Brandon Scott Taysom, Sarah Suffield, Nicole Overman (2021) “High speed manufacturing of aluminum alloy 7075 tubing by Shear Assisted Processing and Extrusion (ShAPE),” Journal of Manufacturing Processes, Volume 71, Pages 699-710, doi: 10.1016/j.jmapro.2021.10.003.