ADVANCED MATERIALS & PROCESSES | JULY/AUGUST 2025 23 TABLE 1 — CHEMICAL COMPOSITIONS, WT%, FOR VARIOUS ALUMINUM SHEET ALLOYSa Alloy Year Si Fe Cu Mn Mg Cr Zn 5052 1934 0.25 0.40 0.10 0.10 2.2-2.8 0.15-0.35 0.10 5754 1970 0.40 0.40 0.10 0.5b 2.6-3.6 0.3b 0.20 5050 1949 0.40 0.7 0.20 0.10 1.1-1.8 0.10 0.25 3104 1990 0.6 0.8 0.25 0.8-1.4 0.8-1.3 0.05 0.25 5182 1967 0.20 0.35 0.15 0.20-0.50 4.0-5.0 0.10 0.25 3105 1966 0.6 0.7 0.30 0.30-0.8 0.20-0.8 0.20 0.40 a An entry with only one number represents the maximum amount, while upper and lower limits are set for major elements. b The summation of Mn + Cr must be maintained within 0.10 to 0.6 wt%. specified high level of chromium (0.15 to 0.35 wt%) with virtually no tolerance for manganese or copper (<0.10%), limiting absorption/mixing of almost all other 5xxx and 3xxx wrought alloy scrap during its production. Consequently, this alloy is normally produced from a high percentage of prime smelter- grade metal. Low Fe and Si is not mandatory for the alloy, but the smelter sourcing generally results in a base aluminum purity of ~99.7%, with Fe = ~0.2% and Si = ~0.15%. The high chromium level means that it can only be absorbed/mixed into some other 5xxx alloys (e.g., 5083 or 5754) and, to some extent, 3105 during recycling. The low Mn and Cu limits, Table 1, prevent scrap from most other 3xxx and 5xxx alloys from being absorbed into a 5052 ingot. The most common indus- trial aluminum sheet scrap is from UBC and consists of 80% 3104 and 20% 5182; UBCs cannot be used in a 5052 melt during recycling due to the 0.10% Mn limit. SHEET PRODUCTION Pure metal is alloyed with Mg and Cr at the smelter or cast house to produce the 5052 ingot needed by the rolling mill. Adding pure Cr is proble- matic due to the wide difference in melting points of Al and Cr. Chromium additions are typically made by adding a “master alloy” or “hardener” containing 5-20% Cr. The production of 100,000,000 lbs of 5052 alloy would require 250,000 lbs of Cr. (or 1.25 million lbs of 20% Cr hardener). These products are purchased from outside vendors and become an extra link and expense in the supply chain for ingot production. Without any energy savings from recycling, the pro- duction of 5052 ingot reflects a carbon footprint of the energy-intensive primary process, including that of electrical power generation, e.g., coal vs hydro. A calculation by Speira Aluminium, a European aluminum sheet supplier, compared the carbon footprint of a typical (600 mm (24-in.) diameter) road sign produced from primary vs recycled material. Their calculation showed a reduction in carbon foot- print from 8.4 to 0.77 kg CO2/kg of aluminum[12]. This >90% reduction in carbon intensity is very much in line with other estimates of recycled content benefits. Another significant issue with the use of Cr is its position on the list of strategic metals. According to the U.S. Geological Survey (USGS) 83% of the Cr used in the U.S. is imported, most of it from South Africa[13]. The imports, in the form of chromite ore, are predominantly used in the produc- tion of stainless steels and other refractory alloys. Because of the limited (geographic) supply base and the possibility for disruptions in its availability, its price is volatile, and Cr is considered a strategic material for U.S. industry. There are no replacements for most of its current applications in stainless steels. 5052 helped create a more serious issue that we still face today: Many of the design and material specs, including alloy selection, were written by government agencies or formalized as general industry standards (described in more detail below). Here it is important to remember that FHWA specs mentioned previously do not automatically apply to state, city, or county road systems, but many municipalities still select 5052 as a default due to its widespread availability[4]. The 2024 North American market for alloy 5052-H38 used as federal signage was estimated at 75 to 100 million pounds. Approximately 25 million pounds per year of 5052-H32 was used for non-federally regulated (state or municipal) applications plus an additional ~50 million pounds of sheet supplied for road/traffic/pedestrian signage (composite estimate for alloys 3003, 3004, 3105, and 5754). THE PROBLEM WITH 5052 The major issue confronting alloy 5052 regarding its carbon footprint can be easily understood with a look at the AA chemical composition limits. Table 1 contains an excerpt from the Aluminum Association Teal Sheets, comparing some selected aluminum sheet alloys[11]. 5052 alloy has a
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