Aluminum 7055
Introduction to Aluminum 7055
Aluminum 7055 is a high-strength, heat-treatable aluminum-zinc alloy specifically engineered for aerospace structural applications. As one of the highest-strength aluminum alloys available, it provides superior compressive properties, excellent fracture toughness, and enhanced stress corrosion cracking (SCC) resistance—particularly in thick-section parts.
Aluminum 7055 is often selected for CNC machining in aerospace frames, fuselage structures, and high-load-bearing components in defense and transportation, where weight savings must not compromise structural performance.
Chemical, Physical, and Mechanical Properties of Aluminum 7055
Chemical Composition (Typical)
Element | Composition Range (wt.%) | Key Role |
|---|---|---|
Aluminum (Al) | Balance | Base metal for lightweight, corrosion-resistant structure |
Zinc (Zn) | 7.7–8.4 | Principal strengthening element in precipitation hardening |
Magnesium (Mg) | 1.8–2.3 | Enhances mechanical strength and fatigue resistance |
Copper (Cu) | 2.0–2.6 | Increases hardness and improves creep resistance |
Zirconium (Zr) | 0.08–0.15 | Refines grain structure and improves corrosion resistance |
Chromium (Cr) | ≤0.04 | Grain boundary control (trace levels) |
Silicon (Si) | ≤0.12 | Residual element |
Iron (Fe) | ≤0.15 | Residual element |
Physical Properties
Property | Value (Typical) | Test Standard/Condition |
|---|---|---|
Density | 2.83 g/cm³ | ASTM B311 |
Melting Range | 475–635°C | ASTM E299 |
Thermal Conductivity | 130 W/m·K at 25°C | ASTM E1952 |
Electrical Conductivity | 37% IACS at 20°C | ASTM B193 |
Coefficient of Expansion | 23.2 µm/m·°C | ASTM E228 |
Specific Heat Capacity | 870 J/kg·K | ASTM E1269 |
Elastic Modulus | 71 GPa | ASTM E111 |
Mechanical Properties (T7751/T7651 Temper)
Property | Value (Typical) | Test Standard |
|---|---|---|
Tensile Strength | 655–700 MPa | ASTM E8/E8M |
Yield Strength (0.2%) | 620–655 MPa | ASTM E8/E8M |
Elongation | ≥7% | ASTM E8/E8M |
Hardness | 170–190 HB | ASTM E10 |
Fatigue Strength | ~240 MPa | ASTM E466 |
Fracture Toughness | High | ASTM E399 |
Key Characteristics of Aluminum 7055
Ultra-High Strength for Aerospace Design: Aluminum 7055 achieves one of the highest yield strengths among all aluminum alloys—up to 655 MPa—ideal for weight-critical fuselage and wing structures.
Superior Stress Corrosion Resistance (ASTM G47): Enhanced with zirconium and optimized heat treatment, 7055 offers excellent SCC resistance in thick sections, outperforming traditional 7075-T6.
High Fracture Toughness: Excellent crack resistance under cyclic loading makes it ideal for high-stress and high-fatigue aerospace joints and brackets.
Moderate Machinability (Rating 60% vs. B1212 Steel): Though not as machinable as 6061 or 2024, it can be precisely CNC machined using optimized parameters and proper chip evacuation.
Heat Treatable and Dimensionally Stable: Aluminum 7055 is commonly supplied in T7751 or T7651 tempers, combining high strength with low residual stresses—suitable for CNC precision machining.
CNC Machining Challenges and Solutions for Aluminum 7055
Machining Challenges
High Strength → High Tool Wear: Accelerated tool degradation without optimized tooling or cooling.
Chip Adhesion and Build-Up: Especially at elevated temperatures in dry or insufficiently cooled operations.
Brittleness in Small Features: Care is required to avoid tool chatter or micro-cracking in thin-walled areas.
Optimized Machining Strategies
Tool Selection
Parameter | Recommendation | Rationale |
|---|---|---|
Tool Material | TiAlN-coated carbide or PCD tools | Heat and wear-resistant for high-speed dry cuts |
Geometry | High rake, positive chipbreaker | Minimizes cutting forces and chip adhesion |
Cutting Speed | 120–220 m/min | Balances productivity with tool life |
Feed Rate | 0.10–0.25 mm/rev | Prevents work hardening or deflection |
Coolant | Flood or high-pressure through-spindle | Reduces thermal load and improves chip removal |
Aluminum 7055 Cutting Parameters (ISO 513 Compliance)
Operation | Speed (m/min) | Feed (mm/rev) | Depth of Cut (mm) | Coolant Pressure (bar) |
|---|---|---|---|---|
Roughing | 120–160 | 0.20–0.25 | 2.0–3.0 | 30–50 (Flood) |
Finishing | 180–220 | 0.05–0.10 | 0.5–1.0 | 50–70 (Flood/Mist) |
Surface Treatment for Aluminum 7055 CNC Parts
Anodizing: Type II anodizing enhances oxidation resistance and finish quality; hard anodizing improves wear resistance to 50 µm.
Powder Coating: Adds robust external protection for aerospace covers and consumer electronics.
Electropolishing: Improves fatigue strength and stress crack resistance in aerospace brackets.
Passivation: Typically used before anodizing to ensure surface cleanliness.
Brushing: Applied to visible aerospace panels and trim parts with Ra 1.0–1.6 µm.
Alodine Coating: Offers conductive and MIL-DTL-5541-compliant surface protection for aerospace electronic parts.
UV Coating: Enhances color retention and surface gloss for control housings or access covers.
Lacquer Coating: Used on aerospace-grade decorative trim with precise tolerances.
Industry Applications of Aluminum 7055
Aerospace and Aviation: Wing ribs, spars, fuselage frames, pressure bulkheads, and seat rails requiring maximum strength-to-weight performance.
Defense: Lightweight armored plates, UAV frames, missile structures, and brackets requiring superior impact resistance and dimensional precision.
Transportation (Rail/Air Cargo): High-load rail car structures, aerospace freight containers, and transport frames.
High-Performance Robotics: Structural arms and high-strength joints in mobile and flight-ready robotic platforms.
Motorsport Engineering: Critical load-bearing elements include roll cage nodes, suspension components, and control housings.
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