Heat Treatment and Machining Techniques for Aluminum 7175 Sheet

Among the high-strength aluminum alloys used in modern engineering, Aluminum 7175 Sheet stands out for its exceptional combination of strength, toughness, and fatigue resistance. Originally developed for aerospace and defense applications, this alloy provides superior performance where high stress, precision, and durability are required.

However, the outstanding mechanical properties of Aluminum 7175 are not achieved by composition alone — they depend heavily on precise heat treatment and machining techniques. These processes determine the final microstructure, strength, dimensional accuracy, and surface finish of the material.

In this article, SASAALUMINUM explores the advanced heat treatment procedures and machining practices used in the production and processing of Aluminum 7175 Sheet, explaining how each step contributes to the alloy’s superior performance in aerospace, transportation, and industrial applications.

Overview of Aluminum Alloy 7175

Aluminum Alloy 7175 is a high-strength aluminum-zinc-magnesium-copper alloy (Al-Zn-Mg-Cu) belonging to the 7xxx series. It is a close relative of 7075 but offers improved fracture toughness and stress-corrosion resistance.

Typical Chemical Composition (%):

  • Zinc (Zn): 5.6 – 6.1

  • Magnesium (Mg): 2.0 – 2.5

  • Copper (Cu): 1.2 – 1.6

  • Chromium (Cr): 0.18 – 0.25

  • Aluminum (Al): Balance

The addition of zinc and magnesium forms MgZn₂ precipitates, which provide significant strengthening through precipitation hardening. This makes Aluminum 7175 ideal for aircraft structural components, landing gear, and high-stress aerospace parts.

At SASAALUMINUM, every sheet undergoes precise heat treatment and mechanical processing to ensure optimum balance between strength and machinability.

The Importance of Heat Treatment

Heat treatment is the most critical stage in developing the desired mechanical and physical properties of Aluminum 7175. Through controlled heating, quenching, and aging, the alloy undergoes structural transformations that determine its final hardness, strength, and ductility.

The primary goal of heat treatment is to achieve a uniform distribution of strengthening precipitates while minimizing internal stress and distortion.

Common Heat Treatment Conditions for Aluminum 7175 Sheet

Aluminum 7175 can be supplied in several heat-treated conditions, but the most widely used tempers are T6, T73, and T74, each offering different balances between strength and corrosion resistance.

1. T6 Temper (Solution Heat-Treated and Artificially Aged)

This condition delivers the maximum tensile and yield strength.

Heat Treatment Process:

  • Solution Treatment: Heated to approximately 470°C–480°C (875°F–895°F) for several hours to dissolve soluble phases (mainly MgZn₂).

  • Quenching: Rapidly cooled in water to retain alloying elements in a supersaturated solid solution.

  • Artificial Aging: Reheated to around 120°C–130°C (250°F–265°F) for 20–24 hours to precipitate strengthening phases uniformly.

Resulting Properties:

  • Extremely high strength and hardness.

  • Excellent fatigue resistance.

  • Slightly lower corrosion resistance than T73 or T74 tempers.

The T6 temper is widely used in aerospace parts where maximum strength-to-weight ratio is required.

2. T73 Temper (Over-Aged for Stress-Corrosion Resistance)

The T73 temper provides better corrosion resistance and improved fracture toughness, though with slightly reduced strength compared to T6.

Heat Treatment Process:

  • Solution Treatment: Similar to T6.

  • Artificial Aging: Two-step aging at 110°C for 8 hours, followed by 160°C for 16 hours.

Resulting Properties:

  • Excellent resistance to stress corrosion cracking.

  • Improved toughness and dimensional stability.

  • Preferred for marine or humid environments.

SASAALUMINUM frequently supplies Aluminum 7175-T73 Sheets for aerospace structures operating under long-term stress and environmental exposure.

3. T74 Temper (Intermediate Aging Condition)

The T74 temper provides a balance between T6 strength and T73 corrosion resistance.

Heat Treatment Process:

  • Artificial aging performed at slightly higher temperatures than T73 but shorter duration.

  • Produces smaller and more coherent precipitates, leading to moderate strength and improved stress-corrosion resistance.

Applications:
Used in critical aerospace components where both strength and corrosion resistance are essential, such as fuselage panels and landing gear parts.

Microstructural Changes During Heat Treatment

During the heat treatment process, Aluminum 7175 undergoes a transformation in its internal structure:

  1. Solution Treatment: Alloying elements such as Zn, Mg, and Cu dissolve into the aluminum matrix, forming a homogeneous solid solution.

  2. Quenching: Rapid cooling traps these elements in a supersaturated state.

  3. Aging (Precipitation): Controlled reheating allows the formation of fine, uniformly distributed MgZn₂ precipitates, which obstruct dislocation movement and increase hardness.

The microstructure developed through this process determines the final mechanical performance of the alloy. At SASAALUMINUM, advanced heat treatment furnaces with precision temperature control ensure consistent phase distribution and mechanical uniformity across large sheet sizes.

Machining Characteristics of Aluminum 7175 Sheet

While Aluminum 7175 provides exceptional strength, its high hardness also presents challenges in machining. Proper tool selection, cutting parameters, and lubrication are vital to maintain precision and surface integrity.

1. Machinability Rating and Challenges

Aluminum 7175 has a machinability rating of approximately 70–75%, relative to free-machining aluminum alloys. Its strong tendency to work harden requires careful process control.

Common machining challenges include:

  • Built-up edge formation on cutting tools.

  • High cutting forces due to material toughness.

  • Surface tearing or tool chatter if incorrect feeds or speeds are used.

2. Recommended Machining Techniques

Tool Selection:

  • Use carbide or diamond-coated tools for maximum wear resistance.

  • Sharp cutting edges reduce heat buildup and improve surface finish.

Cutting Parameters:

  • Cutting Speed: 150–300 m/min (depending on tool material).

  • Feed Rate: 0.05–0.3 mm/rev.

  • Depth of Cut: 0.5–2 mm for roughing, 0.1–0.3 mm for finishing.

Coolant and Lubrication:

  • Employ water-soluble cutting fluids or oil-based coolants to reduce friction and temperature.

  • Maintain proper coolant flow to avoid thermal distortion.

Machining Strategy:

  • Use climb milling to minimize work hardening.

  • Avoid interrupted cuts, which may induce microcracks.

  • Ensure rigid tool setup to reduce vibration and improve dimensional accuracy.

3. Surface Finishing and Post-Machining Treatments

After machining, Aluminum 7175 sheets may undergo surface finishing processes such as:

  • Polishing or Buffing: To achieve a smooth, reflective surface.

  • Anodizing: Improves corrosion resistance and aesthetic appeal.

  • Chemical Conversion Coating: Adds protective oxide layers without altering dimensions.

SASAALUMINUM provides post-machining finishing services to meet aerospace and industrial specifications, ensuring perfect surface quality and performance.

Quality Testing and Standards

Every SASAALUMINUM Aluminum 7175 Sheet is tested to ensure it meets international mechanical and chemical standards.

Mechanical Tests:

  • Tensile Test (ASTM E8): Determines ultimate tensile strength and elongation.

  • Hardness Test (ASTM E10): Confirms proper heat treatment condition.

  • Fatigue and Fracture Tests: Evaluate long-term reliability under cyclic loads.

Microstructure and Chemical Analysis:

  • Spectrographic Analysis (ASTM E1251): Ensures precise composition.

  • Metallographic Examination (ASTM E3/E407): Verifies grain size and precipitate distribution.

Dimensional and Surface Inspections:

  • Conducted using precision instruments to maintain strict tolerances.

  • Surface roughness controlled within Ra ≤ 0.8 μm for aerospace-grade sheets.

These stringent quality controls ensure SASAALUMINUM’s Aluminum 7175 Sheets meet or exceed standards such as AMS 4058, ASTM B209, and EN 485-2.

Industrial Applications of Aluminum 7175 Sheet

Because of its superior combination of strength and processability, Aluminum 7175 is extensively used in:

  1. Aerospace Components: Fuselage skins, wing spars, bulkheads, and landing gear structures.

  2. Defense and Military Applications: Armor panels and structural reinforcements.

  3. Automotive and Motorsport: Lightweight performance components.

  4. Industrial Equipment: Precision parts requiring excellent fatigue resistance.

  5. Tooling and Molds: High-strength base plates for die and mold applications.

SASAALUMINUM supplies precision-cut Aluminum 7175 Sheets in various thicknesses and tempers to meet customer-specific application requirements.

Advantages of SASAALUMINUM Manufacturing

SASAALUMINUM maintains strict process control throughout the manufacturing and machining of Aluminum 7175 sheets, ensuring superior consistency and reliability.

Key Advantages:

  • Advanced Heat Treatment Furnaces: With precise temperature and timing control.

  • High-Precision CNC Machining: Achieves tight dimensional tolerances.

  • Full Traceability: EN 10204 3.1/3.2 certificates for all materials.

  • Custom Thickness and Surface Finishes: Tailored to aerospace and defense specifications.

  • Comprehensive Testing: Compliance with ASTM, AMS, and ISO standards.

Our dedication to precision and quality guarantees that SASAALUMINUM Aluminum 7175 Sheets deliver exceptional performance in even the most demanding environments.

Conclusion

The superior strength, stability, and fatigue resistance of Aluminum 7175 Sheet are a result of precise heat treatment and advanced machining techniques. Proper solution treatment, quenching, and aging develop a strong, fine-grained microstructure, while accurate machining ensures high dimensional integrity and smooth surfaces.

With decades of metallurgical expertise and state-of-the-art facilities, SASAALUMINUM continues to lead the industry in producing premium-grade Aluminum 7175 Sheets for aerospace, automotive, and industrial sectors.

Post time: Nov-04-2025