ADVANCED MATERIALS & PROCESSES | JULY/AUGUST 2025 21 The aluminum industry has taken a serious approach to reducing carbon emissions associated with primary operations (refining and smelting) and in the generation of electricity to power these processes. In North America and Europe, particularly, aluminum production from coalfired electricity has been significantly reduced through closure of smelters and reliance on available hydroelectric power. Smelters are selling pure metal with a certification of its “carbon footprint” measured in kg of CO2 per kg of aluminum[1]. Longer term, the primary industry is working to replace the current consumable carbon anodes used in the existing Hall-Heroult process[2]. In downstream production such as rolling and extrusion, companies are finding options to utilize scrap in place of virgin metal through alloy development and substitution. Many producers have closed the “prompt” scrap loops with customers, taking back alloy- segregated trim scrap and offal for remelting. Scrap from used beverage cans (UBCs) has found its way to replace other sheet and foil alloys in building products, truck panels, and food service containers. Extrusion billet suppliers have similarly partnered with customers to recycle machining chips in the manufacture of truck wheels[3]. The carbon footprint of highway infrastructure in North America, LOWER-CARBON ALUMINUM ALLOYS FOR TRANSPORTATION INFRASTRUCTURE Alternatives to alloy 5052, including existing 3xxx or 5xxx alloys, can improve carbon footprint with no functional difference in performance. R.E. Sanders,* Sanders Aluminum Consulting, Chapin, South Carolina B.V. Costello, Novelis Inc., Atlanta, Retired *Member of ASM International Fig. 1 — Typical state and federal aluminum road signage in use in the United States. Most small signs are produced from aluminum sheet while large (usually green) interstate highway signs are produced from extruded stock. Courtesy of Dreamstime. the use of specific alloys and tempers: 5052-H38 or 6061-T6. For signs less than 30 x 30-in., 0.080-in. (2 mm) thick sheet is specified while larger signs require 0.120-in. (3 mm) sheet[4]. In practice, 6061-T6 sheet is rarely used, even though its use in extruded form is commonplace for large multilane interstate highway signage as described below. particularly road signage, has received relatively little attention from government authorities. The traditional alloys specified for these applications in North America are detailed along with their suitability for closed loop recycling and recommendations for substitution by alternate alloys. Contrast the markets and alloy selection in North America to the situation in Europe, where high recycled content alloys are used for the same end applications. HIGHWAY SIGNAGE The end of World War II ushered in a major worldwide expansion of highway systems to facilitate automotive and truck transportation. In the United States, construction of the Interstate Highway grid during the 1960s-70s ensured the safety and efficiency of long-distance travel. To standardize the procurement and safety of materials used in highway construction, the Federal Highway Administration (FHWA) specified particular aluminum products used for lighting standards, traffic barriers, RR crossings, and road signage (Fig. 1). Road signage standards are found within FHWA documents such as reference 4. On page 713, the code specifies
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