ADVANCED MATERIALS & PROCESSES | JULY/AUGUST 2024 1 7 ShAPE FOR RECYCLING Unlike other high-shear extrusion processes such as equal channel angular extrusion (ECAE) that have limited scalability[7], ShAPE is in the process of being scaled to the industrial level and produces hollow and solid profiles of a variety of shapes including noncircular and multicell profiles. In 2016, Bond Technologies (Elkhart, Indiana) designed and manufactured the first purpose- built ShAPE machine for PNNL. In December 2023, Bond delivered a larger ShAPE 2 machine to PNNL capable of a ram force of 1350 kN, a torque of 12,000 N·m, and a capacity for extruding billets with diameters up to 75 mm. Although small compared to industrial- scale machinery, ShAPE 2 gives PNNL the ability to research process parameters important to scaling such as the ram force, spindle torque, and motor power. ShAPE has been applied to many materials including aluminum alloys, titanium alloys, high entropy alloys, polymers, oxide dispersion strengthened steels, electrical conductors, and thermoelectrics. A schematic of the process is shown in Fig. 1. ShAPE is also flexible to feedstock and has been used to extrude castings, powders, flakes, foils, and chips directly[8]. This flexibility in feedstock material and form factor positions ShAPE to be a promising technology for extruding mixed post- consumer Al scrap[9]. ShAPE has several additional benefits over conventional extrusion that are not specifically related to recycling. One is that most aluminum alloys, such as 2024, 6061, and 7075, can be extruded by ShAPE without subjecting the feedstock ingots to a homogenization heat treatment[10]. Homogenization is typically a time- and energy-intensive treatment (up to 18 hours at 450°C for 7075), and avoiding it can reduce energy, cost, and carbon emissions. Other advantages include precise control of the die temperature through the modulation of the rotational speed and improved materials properties through second-phase particle refinement and dispersion. These benefits make ShAPE a promising technique for manufacturing semifinished components from post-consumer aluminum alloy scrap. CASE STUDY: ShAPE RECYCLING OF MIXED TWITCH SCRAP PNNL has performed a study on the recycling of 100% post-consumer scrap using ShAPE as part of the LightMAT Seedling Program within the U.S. DOE Vehicle Technologies Office. The scrap type of interest was mixed Twitch supplied by Pacific Steel and Recycling. Twitch is shredded scrap from automotive scrapyards, separated using a density flotation method. According to ISRI specifications, it must not contain more than 1% free zinc, 1% free magnesium, and 1% analytical iron[6]. Sometimes the Twitch scrap is separated further into cast and wrought alloys, but this study used mixed Twitch, which is a combination of both. Being a mix of wrought and cast scrap, there is a high content of several alloying elements, and this scrap stream cannot be made into any standard wrought aluminum alloy composition without extensive dilution with primary aluminum. The composition of extrusion billets cast from Twitch scrap was analyzed using inductively coupled plasma optical emission spectroscopy (ICP-OES) and is summarized in Table 1, which compares it with the compositions of three common aluminum alloys. The Twitch was first melted in its as-received condition and cast into cylindrical ingots with a diameter of 38 mm and a length of 178 mm by Eck Industries. These castings were then machined into extrusion billets with an outer diameter of 32 mm, an inner diameter of 10 mm, and a length of Fig. 1 — Schematic of ShAPE for indirect extrusion of seamless tubing with a floating mandrel. Image courtesy of Nathan Johnson/PNNL. Fig. 2 — Left to right: Mixed Twitch Al alloy scrap supplied by Pacific Steel and Recycling; four Al alloy ShAPE-extruded tubes: a 1″ diameter tube, a multicell extrusion, a square tube, a clear anodized tube; and a blue anodized tube made with Twitch scrap.
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