The National Institute of Standards and Technology (NIST) has developed a new reference material to aid quality control in the steel coatings industry. The new Standard Reference Material (SRM) 2426 is a 55% aluminum-zinc alloy certified by NIST not only for the aluminum and zinc content but also for silicon and iron, two important contaminants.
First introduced commercially in the 1970s, 55% Al-Zn is widely used as a tough, corrosion-resistant coating for sheet steel, particular in roofing. The Zinc Aluminum Coaters Association (ZAC) claims the latter as the fastest-growing coated steel product in the world. The alloy is applied to sheet steel using a hot-dip coating process. Huge coils of cold-rolled steel wind through a vat of the molten alloy at speeds up to three meters a second. The coating must meet industrial standards for thickness and chemical composition, so the steel typically is sampled for quality control at regular intervals.
Over time, the molten alloy vat gradually accumulates iron and silicon from the steel, and must be monitored to prevent the concentration of contaminants from getting too high. The new NIST reference material represents 55% aluminum-zinc alloy that is near the maximum allowable concentrations of iron and silicon as set by ASTM*, and can be used by steel laboratories to validate the performance of their test methods at the critical upper specification limits.
NIST SRM 2426 - 55% Aluminum-Zinc Alloy was developed in cooperation with ASTM International Committee E01 on Analytical Chemistry of Metals, Ores and Related Materials. It is intended primarily for use in evaluating chemical and instrumental methods of analysis. Certified values are provided for the four elements aluminum (Al), zinc (Zn), silicon (Si), and iron (Fe). The material from which SRM 2426 was developed is better known by one of several trade names including Galvalume® in North America and, in South America, Zincalume®, Zintro Alum™ and Galval™. From 1972 to 2004, nearly 20 million tons of steel coated with this alloy were produced in North America.
More information on SRM 2426 is available from NIST's Standard Reference Materials office.
*ASTM A924/A924M-04 Standard Specification For General Requirements For Steel Sheet, Metallic-Coated By The Hot-Dip Process.