Steel Sheet, Zinc-Nickel Alloy Coated by the Electrolytic Process for Applications Requiring Designation of the Coati...

A918: Standard Specification for Steel Sheet, Zinc-Nickel Alloy Coated by the Electrolytic Process for Applications Requiring Designation of the Coating Mass on Each Surface

In demanding engineering applications where corrosion resistance and specific surface protection are paramount, understanding the nuances of protective coatings is essential. ASTM A918 provides an authoritative framework for specifying and procuring steel sheet with a specialized zinc-nickel alloy coating applied through an electrolytic process. This industry-leading standard is crucial for professionals seeking predictable performance and tailored corrosion protection for their fabricated metal products.

What is A918?

ASTM A918 is a comprehensive standard that defines the requirements for steel sheet coated with a zinc-nickel alloy using an electrolytic process. Its primary purpose is to facilitate the application of coatings with precisely designated masses on each surface, allowing for differential corrosion protection tailored to specific application needs. This standard ensures a smooth, spangle-free finish with a zinc-nickel composition ranging from 9% to 16% nickel by weight.

Scope & Purpose

This specification governs the production and quality of hot-rolled and cold-rolled steel sheet that has undergone electrolytic zinc-nickel alloy coating. It specifically addresses applications where the coating mass needs to be designated independently for each surface of the steel sheet, enabling differentiated levels of corrosion resistance. While it covers various base metal types and grades, it does not detail the mechanical properties of the base metal itself, nor does it prescribe specific surface treatments beyond the coating.

Who Must Comply?

• • Primary audience: Materials Engineers, Metallurgists, Quality Control Inspectors, Design Engineers, and Production Managers involved in the specification, procurement, or fabrication of coated steel products.
• • Industries affected: Automotive, Manufacturing, Construction, Aerospace, and any sector requiring enhanced corrosion protection for steel components.
• • Compliance nature: This is a voluntary standard, but its adoption is highly recommended for ensuring product quality, performance, and interoperability within affected industries.
• • Enforcement: Compliance is typically verified by manufacturers through internal quality control processes and by end-users or third-party inspectors during material acceptance.

Key Requirements Overview

Professionals utilizing ASTM A918 must ensure adherence to several core provisions:

• • The standard requires that the zinc-nickel alloy coating be applied via an electrolytic process, resulting in a smooth, spangle-free surface.
• • Key provisions include the ability to specify equal or differential coating masses on each surface, with the composition of the coating being between 9% and 16% nickel.
• • Professionals must ensure that coating masses conform to designated values, which can range from light coatings intended for painted applications to heavier coatings for bare service.
• • The specification mandates that ordering information clearly defines the base metal type, grade, coating designation, and any required dimensions and tolerances.
• • Testing methods for verifying coating mass and composition, such as X-ray fluorescence and chemical analysis, are referenced, ensuring proven quality control.

Related Standards & References

ASTM A918 works in conjunction with other vital standards to provide a comprehensive approach to coated steel products. ASTM A917, "Specification for Steel Sheet, Coated by the Electrolytic Process for Applications Requiring Designation of the Coating Mass on Each Surface (General Requirements)," provides foundational requirements that A918 elaborates upon. Furthermore, **