7075 Aluminum Plate

Overview of 7075 Aluminum Plate

7075 aluminum plate is an Al-Zn-Mg-Cu series ultra-high strength aluminum alloy. Since its inception in 1943, it has become a core material in high-end manufacturing sectors such as aerospace and national defense, thanks to its outstanding performance—offering strength approaching that of steel at only one-third of the weight.

Core Performance Advantages

• Ultra-High Strength:Tensile strength ranges from 540 to 590 MPa, close to that of common structural steel.
• Lightweight:Density is 2.81 g/cm³, merely 36% of the weight of steel.
• Outstanding Specific Strength:The strength-to-density ratio reaches 203 MPa·cm³/g, which is 4.6 times that of ordinary steel.

Specifications and Parameters

Standard Plate Size Range

Thickness Series:

• Ultra-thin plate: 0.5 - 3.0mm
• Thin plate: 3.0 - 6.0mm
• Medium plate: 6.0 - 25mm
• Thick plate: 25 - 100mm
• Ultra-thick plate: 100 - 250mm

Width Specifications:

• Standard widths: 1000, 1200, 1500, 2000mm
• Wide-format plates: 2500, 3000, 4000mm
• Custom widths: Available upon customer request

Length Specifications:

• Standard lengths: 2000, 2500, 3000, 6000mm
• Cut-to-length: Supplied according to drawing dimensions (with a +30-50mm machining allowance)
• Coils: Available for thicknesses ≤6mm

Tolerances and Surface Quality Standards

Thickness Tolerance (ASTM B209):

Flatness Requirements:

• Ordinary Grade:≤3mm/m
• Precision Grade:≤1mm/m
• Ultra-Flat Plate:≤0.1mm/m² (requires stretch-leveling treatment)

Surface Quality Grades:

• Grade A:No visible defects; used for cosmetic and anodized parts.
• Grade B:Minor scratches and dents allowed; used for general structural parts.
• Grade C:Certain defects allowed; used for non-cosmetic, non-critical areas.

Special Specification Products

Ultra-Thick Pre-Stretched Plate (6 - 250mm):

• Features:Undergoes 1.5-3% permanent stretching deformation; residual stress <30 MPa.
• Width:1500 - 4000mm
• Flatness:≤0.5mm/m
• Applications:Aircraft wing spars, large mold base plates, precision machinery frames.

Ultra-Flat Thin Plate (0.5 - 6mm):

• Flatness:≤0.1mm/m²
• Process:Multi-pass rolling + stretch leveling + stress relief.
• Applications:Precision electronics housings, optical instrument base plates.

Chemical Milling Plate:

• Thinning Accuracy:±0.02mm
• Surface Roughness:Ra 0.4 - 0.8 μm
• Process:Material removed via chemical etching to avoid mechanical stress.
• Applications:Aircraft skins (variable thickness design), spacecraft panels.

Military Armor Composite Plate:

• Structure:7075-T6 + Ceramic/Composite materials
• Ballistic Performance:V50 ≥ 650 m/s
• Applications:Light armored vehicles, protective equipment.

Chemical Composition and Strengthening Mechanism

Main Alloying Elements

Aerospace Grade Requirement: Composition controlled within ±0.1% accuracy to ensure batch-to-batch consistency.

Strengthening Mechanism

Precipitation Strengthening (Primary Mechanism):

• Solid solution treatment (465-480°C) → Quenching → Artificial aging (120°C/24h).
• Precipitation of the η' (eta prime) phase (5-10nm in diameter) provides the main strengthening effect.
• The T6 temper yield strength can reach up to 503 MPa.

Comparison with Common Aluminum Alloys

Heat Treatment Tempers and Performance

7075-T6 Temper: Peak Strength State

• Process:
1. Solid solution: 470±3°C, 1-2 hours.
2. Quenching: Transfer time ≤10 seconds, water temp 20-40°C.
3. Artificial aging: 120±3°C for 24 hours.
• Performance:Tensile Strength: 572 MPa / Yield Strength: 503 MPa / Elongation: 11% / Hardness: 150 HB / Fatigue Strength: 160 MPa (at 5×10⁸cycles).
• Applications:Aircraft primary structures, high-performance racing suspensions, precision instrument frames.
• Limitations:High susceptibility to stress corrosion cracking (SCC); not suitable for marine or high-humidity environments.

7075-T651 Temper: First Choice for Precision Machining

Based on T6, it includes a 1.5-3% stretching deformation to eliminate residual stress.

• Technical Advantages:Residual stress drops from 80-120 MPa to ≤30 MPa; machining deformation is reduced by 60-80%; flatness can reach ≤0.1mm/m²; mechanical properties remain largely identical to T6.
• Engineering Value:When 70% of the material is removed via CNC, deformation is controlled to 0.05-0.2mm (down from 0.5-2mm).
• Applications:Machined aircraft structural parts, mold bases, semiconductor equipment frames.

7075-T73/T7351 Temper: Anti-Corrosion Optimization

• Process:Double-step aging (Step 1: 107°C × 8h; Step 2: 177°C × 8h).
• Performance Balance:Tensile strength drops to ~505 MPa (down 12%), yield strength drops to ~435 MPa (down 15%). However, the SCC threshold increases from 15-20 to 24 MPa·m^0.5, improving SCC resistance by 3-5 times.
• Application Standards:Mandatory for load-bearing structures exposed to the atmosphere by manufacturers like Boeing and Airbus.

Mechanical Properties

Strength and Load-Bearing Capacity

• Actual Load Calculation (10x10mm 7075-T6 cross-section):Theoretical load capacity = 572 MPa × 100 mm² = 57,200 N ≈ 5.8 metric tons of force.
• Recommended Design Stress:Allowable stress = Yield strength × 0.6 to 0.7 (Safety factor 1.5-1.67). For 7075-T6, the recommended design stress is 300-350 MPa.

Key Fatigue Performance Data

• S-N Curve Characteristics (No distinct fatigue limit):10⁶cycles: 200 MPa; 10⁷cycles: 170 MPa; 10⁸cycles: 160 MPa.
• Influencing Factors:Stress concentration (reducing fillet radius from 2mm to 0.5mm lowers lifespan by 50-70%); Surface finish (improving Ra from 1.6μm to 0.4μm increases lifespan by 30-50%); Corrosive environments (salt spray reduces fatigue strength by 40-60%).

Directionality of Fracture Toughness

Toughness Optimization: The T73 temper can push KIC values to 34-38, a 40-50% improvement.

Physical Properties and Design Parameters

While the tensile strength of 7075-T6 (572 MPa) surpasses Q235 and even some Q345 mild carbon steels, its density is only 2.81 g/cm³ (compared to steel's 7.85 g/cm³).

• Specific Strength:4-5 times that of standard structural steel, roughly equivalent to expensive titanium alloys (Ti-6Al-4V).
• High Hardness/Wear Resistance:150 HB Brinell hardness is among the highest for aluminum, suitable for wear-resistant guide rails and sliding components.
• Thermal Conductivity:130 W/(m·K); lower than 6061 but far superior to steel.
• Modulus of Elasticity:71.7 GPa, only 1/3 that of steel. When designing structures requiring high stiffness (minimal deflection), compensation must be made by increasing the cross-sectional area or changing the geometry (e.g., I-beams).

Practical Machining and Processing Guide

Recommended CNC Parameters

Tool Selection:Roughing (YG8 carbide coated tools); Finishing (YG6 or PCD - Polycrystalline Diamond); Threading (Form/roll taps to increase thread strength by 30%).

Deformation Control Techniques:

1. Symmetrical Machining:Alternate machining on both sides to balance stresses.
2. Intermediate Aging:Leave a machining allowance, then hold at 150-180°C for 2-4 hours after roughing.
3. Optimized Clamping:Avoid over-clamping which introduces stress.
4. Uniform Cooling:Use abundant coolant spray.

Welding and Joining

Highly difficult to weld due to:Hot cracking rates of 30-60%; Weld seam strength only retaining 25-35% of the base metal; Severely increased susceptibility to stress corrosion cracking. (Mechanical fastening is generally recommended).

Corrosion Resistance and Protection

Four-Tier Protection System:

1. Material Selection:High-risk environments must use T73/T7351.
2. Stress Control:Keep design stress ≤40% of yield strength.
3. Surface Protection:Anodizing + sealing, or Alclad treatment.
4. Environmental Management:Avoid chloride ions, control humidity <70% RH.

Exfoliation Corrosion Ratings (ASTM G34):

• EA (No exfoliation):Typical of T76 temper.
• EB (Slight exfoliation):Typical of T73 temper.
• EC-ED (Severe exfoliation):Typical of T6 temper.

Galvanic Corrosion Control:

• Use insulating gaskets (PTFE) when in contact with stainless steel or titanium.
• Apply protective coatings on contact surfaces.
• Install sacrificial anodes (zinc/magnesium blocks).

Typical Application Fields

Aerospace

• Wing Spars: 7075-T7351, thickness 15-50mm, single piece length >15m (e.g., Boeing 737).
• Wing Ribs and Stringers: CNC weight-reduction pocket design, reducing weight by 40-60%.
• Fuselage Frames: Riveted connections, using Hi-Lok bolts.

Defense & Military

• Armored Vehicle Bodies: 7075-T6, thickness 10-20mm, 40% lighter than steel vehicles.
• M16 Rifle Receivers: Weight is only 35% of their steel counterparts.
• Speedboat Keels: 7075-T7351 Alclad plate, highly resistant to seawater corrosion.

Mold Making

• Excellent Thermal Conductivity: 130 W/(m·K), ensuring uniform cooling.
• Fast Machining Speed: 3-5 times faster than machining steel.
• Service Life: Capable of 1 to 3 million cycles.

New Energy Vehicles (NEVs)

• Suspension Control Arms: 40% weight reduction, leading to improved handling response.
• Battery Tray Frames: High strength and excellent impact resistance.
• Weight Reduction Benefits: Every 100kg reduced adds 8-12km to the driving range.

Procurement Decision Guide

When purchasing 7075, temper and certification systems are just as critical as price.

1.Temper Selection

• Dry environment + extreme strength needed =Choose T6
• Heavy material removal required (CNC machined parts) =Must choose T651
• Outdoor/marine environment + load-bearing =Choose T73 or T7351
• Requires cold bending or deep drawing =Choose O temper(requires re-heat treatment after forming).

2.Specs and Tolerance Tips

• Thickness:Standard medium-to-thick plates (6-100mm) are most common. For plates over 100mm, center quenchability is an issue; request a hardness gradient report (high-quality plates have a hardness drop of ≤5 HB from surface to core).
• Ultra-Flat Plates:For semiconductor and optical equipment, request custom "ultra-flat thin plates" (flatness ≤0.1mm/m²).

3.Supplier Audit Checklist (Avoiding Pitfalls)

For high-end applications (especially aerospace/military), require the supplier to provide:

1. Mill Certificate:Verify the heat/batch number.
2. Full Test Reports:Chemical composition (spectroscopy) and mechanical properties (tensile testing).
3. NDT Reports:Aerospace grades require 100% Ultrasonic Testing (UT) to ensure no internal porosity or inclusions.
4. QMS Certifications:Such as AS9100 (Aerospace Quality System), Nadcap (Special Processes), or ASTM B209 compliance declarations.

Frequently Asked Questions (FAQ)

Q1: Can 7075 directly replace Q235 or 45# steel?

A:Partially. It is a perfect substitute in "lightweighting" scenarios under tensile/compressive loads. However, if the component requires extremely high stiffness (resistance to bending) or extreme surface wear resistance, a direct dimensional replacement will lead to greater deflection, as 7075's elastic modulus is only 1/3 that of steel.

Q2: Why does the surface of machined 7075 look mottled and grayish?

A:7075 contains high amounts of zinc and magnesium, making it unsuitable for high-gloss, cosmetic decorative anodizing. If appearance is critical, switch to 6061, or use a sandblasting + black/dark gray hard anodizing process to mask the natural material color.

Q3: Should I choose 7075 or 7050?

A:If your plate thickness is under 100mm, 7075 offers the best cost-performance. If you are machining aerospace forgings or ultra-thick plates reaching 150mm or 200mm, the core strength of 7075 will drop significantly. In such cases, you must choose7050, which has far better quenchability (depth of hardening).

Q4: Why does my newly bought T6 plate warp immediately on the CNC machine?

A:You bought the wrong temper. For CNC machining (especially asymmetrical material removal), you must purchase theT651temper (pre-stretched to relieve internal stress). If a supplier passes off T6 as T651, it will warp immediately upon machining. Always run a first-article validation before full production.

Quick Reference Technical Parameters

7075 Standard Chemical Composition (GB/T 3190-2020 / ASTM B209)

Properties by Temper

Physical Properties Summary

• Density:2.81 g/cm³
• Melting Point:477 - 635°C
• Thermal Conductivity:130 W/(m·K)
• Coefficient of Thermal Expansion:23.6 × 10⁻⁶/K
• Modulus of Elasticity:71.7 GPa
• Electrical Conductivity:33% IACS

International Grade Equivalents

• China:7075 / 7A09 (GB/T 3190)
• USA:7075 (ASTM B209)
• EU:EN AW-7075 (EN 573-3)
• Japan:A7075 (JIS H4000)

Conclusion

7075 aluminum plate is an ultra-high-strength material with exceptional performance. By correctly selecting the temper (T6 for pure strength, T73 for corrosion resistance), strictly controlling machining processes, and applying proper anti-corrosion measures, engineers can fully leverage its lightweight advantages. It remains the absolute material of choice for aerospace, military, and high-end mold-making applications.