ASTM F468 – Mechanical & Material Property

The mechanical property requirements for fasteners under the ASTM F468 specification are determined by the specific alloy, the length of the product, and its nominal diameter. These properties are essential for ensuring that nonferrous bolts, screws, and studs can withstand the intended service loads without failure.

To verify compliance, the specification defines two primary testing methods: Full-Size Testing is preferred for fasteners with a breaking load of 120,000 lbf or less to measure actual tensile and yield strength, while Machined Specimen Testing is used for fasteners exceeding that load or where full-size testing is impractical. In any instance where both tension and hardness tests are conducted, the tension test results take precedence for final Acceptance Priority.

The mechanical integrity of these fasteners is governed by several critical factors: Yield Strength Calculation for full-size products uses the specific Tensile Stress Area (A_s) for the product diameter and thread pitch, with the yield point defined at an offset of 0.2% gage length. Ductility is measured as "Elongation in 4D," using a gage length equivalent to four times the diameter of the test specimen.

For alloys other than aluminum and titanium, fasteners too short for tension testing must conform to specific Hardness Requirements. For aluminum alloys, when tension testing is not feasible, a shear test must be performed, requiring minimum strengths such as 37 ksi for 2024-T4 or 41 ksi for 7075-T73.

The material and chemical properties of fasteners under the ASTM F468 specification are strictly defined to ensure consistency and performance across a wide range of nonferrous alloys. These requirements govern the elemental makeup of the finished products, providing the foundation for their unique mechanical and corrosion-resistant characteristics.

To maintain high quality standards, the specification mandates several layers of chemical verification:

• Strict Elemental Limits: Fasteners must conform to the specific chemical requirements detailed in Table 1 for their designated alloy.
• Balance Elements: For many alloys, the primary element (e.g., Copper, Aluminum, or Titanium) is calculated arithmetically as the "balance" by subtracting the total of all other named elements from 100%.
• Verification Methods: Manufacturers may perform analysis on randomly selected finished fasteners or report the analysis of the raw material, provided that heat and lot identities have been strictly maintained.
• Residual Elements: Elements present in small quantities inherent to the manufacturing process but not intentionally added are considered residuals. These typically do not need to be reported unless explicitly required by the purchaser.

Different alloy groups have specific requirements that must be followed for full compliance:

• Nickel Alloys: For all nickel-base alloys, cobalt is to be counted as nickel. Additionally, Alloy 625 material must be refined using either electroslag remelting (ESR) or vacuum arc remelting (VAR) processes.
• Aluminum Alloys: For aluminum fasteners, manufacturers have the option to furnish a certificate of conformance instead of detailed test reports to certify compliance with the chemical composition.
• Copper Alloys: Certain silicon bronze alloys, such as C65100, have specific provisions where an alloy containing up to 2.6% silicon is acceptable under certain elemental sum conditions.