Advanced Manufacturing Process of Aircraft Grade Aluminum 7175 Sheet

In the modern aerospace industry, the demand for materials that combine lightweight performance with high strength and superior fatigue resistance continues to rise. One of the materials that meets these stringent requirements is Aircraft Grade Aluminum 7175 Sheet — a high-strength alloy that offers an exceptional balance between mechanical integrity, corrosion resistance, and machinability.

Developed as an enhanced version of 7075 aluminum, Aluminum 7175 is widely recognized for its use in critical aircraft components such as fuselage skins, wing spars, bulkheads, and landing gear structures. Its reliability is the result of a sophisticated and precisely controlled manufacturing process.

In this article, SASAALUMINUM explores the advanced manufacturing process of Aircraft Grade Aluminum 7175 Sheet, detailing every stage from alloy preparation and heat treatment to machining and quality inspection — ensuring world-class performance for aerospace applications.

Understanding Aircraft Grade Aluminum 7175

Aluminum 7175 is a high-strength aluminum-zinc-magnesium-copper alloy (Al-Zn-Mg-Cu) that achieves superior tensile strength through precipitation hardening. Compared to 7075, it provides enhanced fracture toughness and stress corrosion resistance, making it ideal for high-load-bearing structures in aircraft.

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 combination of these elements allows the alloy to achieve strength levels comparable to some steels while maintaining the lightweight characteristics vital to aviation.

At SASAALUMINUM, strict control of alloy chemistry, heat treatment, and manufacturing processes ensures consistent performance and reliability across every sheet.

Step 1: Raw Material Selection and Alloy Melting

The foundation of a superior 7175 sheet begins with the selection of high-purity raw materials. Premium-grade aluminum, zinc, magnesium, and copper are used to guarantee chemical consistency and eliminate impurities that could compromise performance.

Melting Process:

• The alloying elements are melted in an induction furnace under controlled temperature and atmospheric conditions.

• The molten alloy is degassed using inert gases such as argon or nitrogen to remove dissolved hydrogen and prevent porosity.

• Grain refiners (like titanium and boron) are added to promote fine-grain structure.

Once the melt achieves chemical uniformity, it is cast into large rectangular ingots through a semi-continuous casting process, ensuring minimal segregation and uniform grain distribution.

Step 2: Homogenization Heat Treatment

Before hot rolling, the cast ingots undergo homogenization to dissolve segregated phases and improve workability.

Process Details:

• Temperature: 460°C–480°C (860°F–895°F)

• Duration: 12–24 hours, depending on ingot size

• Cooling: Controlled air cooling to prevent internal stress

This process results in a uniform microstructure, eliminates casting defects, and prepares the ingot for deformation processing.

Step 3: Hot Rolling Process

Hot rolling transforms the homogenized ingot into a sheet while refining the grain structure and enhancing mechanical strength.

Process Steps:

1. Preheating: The ingot is reheated to 420°C–450°C to ensure optimal plasticity.

2. Rolling: The ingot passes through a series of reversing and tandem rolling mills, reducing thickness progressively.

3. Temperature Control: Continuous temperature monitoring ensures uniform deformation without cracking.

4. Cooling: After the final pass, sheets are air-cooled or water-sprayed to retain dimensional stability.

At SASAALUMINUM, advanced rolling lines with automated thickness control ensure precise gauge accuracy and surface flatness, producing sheets suitable for high-precision aerospace fabrication.

Step 4: Intermediate Annealing

Between hot and cold rolling, intermediate annealing may be required to restore ductility and relieve stress.

Typical Parameters:

• Temperature: 350°C–400°C

• Duration: 2–4 hours

• Cooling: Controlled air cooling

This step prevents strain hardening and cracking during further processing.

Step 5: Cold Rolling for Precision Thickness

After annealing, the sheets undergo cold rolling at room temperature to achieve final thickness and surface finish.

Cold rolling enhances:

• Dimensional Precision: Tight tolerances for aerospace standards.

• Surface Quality: Smooth finish with fine grain structure.

• Mechanical Strength: Work hardening refines grain size, increasing toughness.

SASAALUMINUM employs multi-stand cold rolling mills equipped with automatic gauge control (AGC) and flatness sensors, ensuring uniform sheet thickness and mirror-like smoothness.

Step 6: Solution Heat Treatment and Quenching

To achieve the desired balance between strength and toughness, Aluminum 7175 Sheets undergo solution heat treatment, followed by rapid quenching.

Process Sequence:

1. Solution Treatment:

   • Heated to 475°C–480°C to dissolve alloying elements like Mg, Zn, and Cu into a solid solution.

2. Quenching:

   • Rapid cooling (usually water quenching) to trap these elements in a supersaturated state, forming the foundation for later precipitation hardening.

Proper control of heating and quenching rates is critical. Any uneven cooling can cause residual stresses or warping, which is why SASAALUMINUM uses automated quench systems with precise temperature uniformity.

Step 7: Artificial Aging (Precipitation Hardening)

The quenched sheets are then artificially aged to precipitate fine strengthening phases, primarily MgZn₂ (η phase).

Aging Parameters:

• Temperature: 120°C–130°C for T6 temper or 110°C–160°C in dual-stage aging for T73/T74 tempers.

• Time: 20–24 hours, depending on desired mechanical properties.

Resulting Effects:

• Formation of fine, coherent precipitates that hinder dislocation movement.

• Dramatic increase in yield and tensile strength.

• Enhanced fatigue resistance and dimensional stability.

This stage defines the final mechanical performance of Aircraft Grade Aluminum 7175 Sheet.

Step 8: Surface Treatment and Finishing

Surface finishing not only improves aesthetics but also enhances corrosion resistance and bonding characteristics for further fabrication.

Common Finishing Processes:

• Mechanical Polishing: Removes surface oxides and ensures smoothness.

• Anodizing: Creates a protective oxide layer for corrosion resistance.

• Chemical Conversion Coating: Provides excellent paint adhesion and uniform surface properties.

SASAALUMINUM offers customized finishing options based on aerospace standards such as MIL-A-8625 and ASTM B580, ensuring compatibility with downstream processing like riveting, bonding, and forming.

Step 9: Precision Machining and Cutting

To meet aircraft manufacturers’ specific design tolerances, Aluminum 7175 Sheets undergo precision machining and cutting.

Key Techniques:

• CNC Milling and Routing: Achieve accurate dimensions and complex geometries.

• Laser and Waterjet Cutting: Provide precise, burr-free edges with minimal heat distortion.

• Deburring and Edge Polishing: Maintain clean, safe edges suitable for assembly.

At SASAALUMINUM, automated CNC systems ensure dimensional tolerances within ±0.05 mm and excellent repeatability for batch production.

Step 10: Inspection and Quality Assurance

Every Aircraft Grade Aluminum 7175 Sheet undergoes comprehensive inspection to verify compliance with aerospace standards.

Tests and Standards Include: