ADVANCED MATERIALS & PROCESSES | JULY/AUGUST 2024 18 102 mm. To test the ability of ShAPE to refine second phases, no homogenization step was performed on the billets prior to extrusion. Billets were extruded using ShAPE into seamless tubing with outer and inner diameters of 12 and 10 mm, respectively (wall thickness: 1 mm), with a length of about 2 m (Fig. 2). The extrusion ratio was 20, the extrudate velocity was 7.2 m/min, the die rotation rate was 190 RPM, and the steady-state die temperature (measured using a thermocouple welded to the die face) was 520°C. Tubing was water- quenched immediately after exiting the die; then, specimens underwent a peak aging treatment at 180°C for 8 hours. A flowchart of the ShAPE aluminum recycling route compared to conventional extrusion is shown in Fig. 3. The microstructures were observed using backscatter scanning electron microscopy (SEM) and are shown in Fig. 4. ShAPE acted to refine the structure, where the light-colored needle-shaped particles in the as-cast material (which were identified using electron dispersive spectroscopy to be the deleterious β-Al5(Fe,Mn)Si phase[9]) have been broken up into smaller, blocky particles in the ShAPE material. The refinement and morphology change from needle- shaped to blocky is expected to reduce the stress concentrations and increase the ductility of the ShAPE-processed material. The ShAPE-processed tubes from unhomogenized billets were then independently tensile-tested by Westmoreland Testing and Research Inc. according to ASTM standards E8-22 and B557-15 on four replicates[11]. Remarkably, the yield and ultimate tensile strengths of the 100% Twitch TABLE 1 — TWITCH REMELT COMPOSITION MEASURED USING ICP-MS, WT% Alloy Cu Fe Mg Mn Si Zn Others Al Twitch 1.48 0.56 0.88 0.20 4.56 0.48 3.5 88.3 6063 <0.1 <0.35 0.7 <0.1 0.4 <0.1 <0.15 bal. 6061 0.3 <0.7 1.0 <0.15 0.6 <0.25 <0.15 bal. 6082 <0.1 <0.5 0.9 0.7 1.0 <0.2 <0.15 bal. Note: The nominal compositions of three commercial 6xxx-series Al alloys are given for comparison. Fig. 3 — Flowchart of the conventional aluminum production route versus the ShAPE recycling route. Images courtesy of the Library of Congress and Andrea Starr/PNNL. Fig. 4 — SEM backscatter images of the as-cast Twitch billet (left) and ShAPE-processed Twitch tube (right).
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