EN 3999:2007

Overview

EN 3999:2007 is a European standard developed by CEN, specifying the technical requirements for aerospace-grade aluminium alloy AL-P2024-T351 in sheet and strip formats. This standard covers thicknesses ranging from 1.6 mm to 6 mm and focuses on materials with improved chemical milling capability. Designed specifically for aerospace applications, this standard ensures that the aluminium alloy meets stringent criteria, including minimum residual stress levels, to optimize performance during chemical milling processes.

The standard is part of a comprehensive aerospace metallic materials series, aligning with EN 4258 and presented according to EN 4500-2 guidelines. EN 3999:2007 was approved by national standardization bodies across Europe, aiming to harmonize the quality and specifications of aerospace aluminium alloys used in critical structural components.

Key Topics

• Material Designation and Composition
  EN 3999:2007 defines the chemical composition limits of AL-P2024-T351, including specified maximum percentages for elements such as silicon, iron, copper, manganese, magnesium, chromium, zinc, and titanium to ensure optimal mechanical properties and corrosion resistance.

• Sheet and Strip Specifications
  Covers rolled sheets and strips with thicknesses from 1.6 mm to 6 mm, tailored for aerospace structural components requiring precise chemical milling capabilities.

• Improved Chemical Milling Capability
  The alloy is manufactured under controlled conditions to achieve low residual stress levels, a critical requirement for chemical milling applications where dimensional control and surface integrity are essential.

• Heat Treatment and Delivery Condition
  Specifies the T351 temper condition, which includes solution heat treatment, quenching, and controlled stretching to reduce internal stresses and enhance machinability.

• Mechanical Properties Requirements
  Minimum proof stress of 290 MPa, tensile strength of 445 MPa, and elongation of at least 14% ensure the material fulfills the robust demands of aerospace components.

• Corrosion Resistance and Quality Control
  The standard includes limits on intergranular corrosion penetration depth and external surface defects. It also mandates consistent hardness, electrical conductivity, and dimensional tolerances in line with EN 4400-2.

• Testing and Inspection
  Refers to EN 4400-2 for detailed procedures on test samples, heat treatment validation, marking, and dimensional inspections to guarantee compliance.

Applications

Aluminium alloy AL-P2024-T351 sheets and strips conforming to EN 3999:2007 are primarily used in aerospace manufacturing where:

• Chemical Milling is employed to achieve precise component shapes and thickness reduction without compromising the material integrity.
• Structural Components such as aircraft fuselage skins, wing panels, and other load-bearing parts benefit from the enhanced mechanical properties and corrosion resistance.
• Lightweight Designs require high strength-to-weight ratios, which this alloy provides, supporting improved fuel efficiency and performance in aviation.
• Residual Stress-sensitive Parts where maintaining dimensional stability during and after chemical machining is critical to ensuring safety and durability.

Related Standards

• EN 4258 – Aerospace series metallic materials general organization and interlinking of standards, providing foundational structure for EN 3999:2007.
• EN 4400-2 – Technical specification for aluminium and aluminium alloy wrought products including sheets and strips, critical for testing and inspection criteria referenced in EN 3999.
• EN 4500-2 – Rules for drafting and presentation of metallic material standards, facilitating clarity and uniformity in material specifications.
• ASD-STAN – The Aerospace and Defense Industries Association of Europe standardization body responsible for the preparation and approval process of EN 3999.

Keywords: EN 3999:2007, aerospace aluminium alloy, AL-P2024-T351, chemical milling, aluminium sheet and strip, aerospace materials standard, residual stress control, aerospace aluminium specifications, chemical milling capability, aluminium alloy mechanical properties, aerospace manufacturing materials.