Introduction
The fuselage skin of passenger aircraft, main wing spars, and millions of rivets—the vast majority of those giant wings you see at the airport are still made of aluminum alloys. It has been over 100 years since the birth of Duralumin in 1906. Even with the rise of new materials like carbon fiber reinforced plastics (CFRP) and titanium, why does aluminum still hold its position as the “main character”?
The first reason is the balance between specific strength and processability. Pure aluminum at the end of the 19th century was too soft to be a structural material. However, with the advent of Duralumin-based alloys, where precipitation hardening was controlled by adding Cu and Mg, it achieved high strength at one-third the density of steel. This has supported the common wisdom that “lightness equals range” from the early days of the Wright brothers to modern jetliners. Furthermore, since the 1970s, Al-Li alloys with added Li have been developed, with a dramatic performance improvement of -3% density and +6% elastic modulus for every 1 wt% of Li reported (NASA Technical Reports Server).
The second reason is durability and maintainability. Aluminum is suitable for rolling, cutting, and riveting, and there is a wealth of accumulated knowledge on surface treatment and stress diffusion design. SUS MAGAZINE No. 27 also points out that “even in the age of CFRP, the ease of corrosion management and on-site repair keeps aluminum at the forefront” (fa.sus.co.jp). In other words, the key differentiator from other materials is its ability to maximize weight reduction while keeping airline MRO (Maintenance, Repair & Overhaul) costs down.
Although CFRP accounts for about 50% of the airframe mass in aircraft like the B787 and A350, nearly 30% of the remainder is 7000 series aluminum extrusions used for wing spars and floor beams. Designers must pursue not only “lightness” but also long life that can withstand drastic temperature differences and hundreds of thousands of load cycles.
This article will unravel the two value axes of aluminum alloys, “weight reduction × durability,” from four layers: the history of material evolution, the latest processing technologies, environmental costs, and ASEAN procurement strategies. By the time you finish reading, the reasons why aluminum is still indispensable in the current era of CFRP dominance, and hints for the supply chain looking ahead to the next decade, will become clear. Now, let’s guide you into the world of aluminum alloys, where a 100-year tradition intersects with frontline trends.
The Evolution of Aluminum Alloys and Their History in Aircraft
From Duralumin to Super Duralumin
Duralumin (now JIS A2017), developed in 1906 by the German company Dürener by adding Cu-Mg, achieved a tensile strength of ≈ 320 MPa with a specific gravity of 2.8, less than half that of iron, and was put to practical use in the frames of airships during World War I. In the 1930s, A2024 “Super Duralumin” with higher Mg and Zn content was developed, followed in 1943 by A7075 “Extra Super Duralumin” with over 6% Zn, achieving static strength of 570 MPa and a fatigue limit of 230 MPa, comparable to steel. Although there was the issue of reduced corrosion resistance due to copper, its excellent machinability and riveting properties led to its mass adoption in the skins and spars of aircraft like the DC-3 and 747. The achievement of Duralumin-based alloys in simultaneously satisfying “lightweight × processability × mass production cost” can be said to be the foundation of the current 2000/7000 series base technology. (Kasyu Kogyo Co., Ltd.)
The Rise of Aluminum-Lithium (Al-Li) Alloys and Examples of Mass Production Aircraft Adoption
In the 1970s, Al-Li alloys with over 1 wt% Li were developed to achieve a 3% reduction in density and a 6% increase in elastic modulus. The third-generation 2050-T84/2196-T8 alloys reduce structural weight by 10–20% and increase bending stiffness by 15–20% compared to the conventional 2024-T3, and have been mass-produced for the A380 main wing skin and C-Series (now A220) fuselage panels. Another key to their expanded adoption was their thermal expansion coefficient being close to that of CFRP, which helps mitigate stress imbalances in hybrid wing boxes. (ScienceDirect)
Redefining the Role of Aluminum Alloys in the CFRP Era
While CFRP accounts for about 50% of the airframe mass in aircraft like the B787 and A350, aluminum alloys, which allow for rapid crack detection and on-site repair, remain important. For example, in the B787, more than 4,500 m of 7000 series extrusions are used for wing spars and floor beams, functioning as intermediate flanges for bolting CFRP components. Furthermore, FSW (Friction Stir Welding) and automated riveting have reduced assembly time by 30% while extending fatigue life. In the future, “buy-to-fly design,” where Al-Li blanks are left with only the necessary thickness through topology optimization and additive manufacturing, will become mainstream, and aluminum is being redefined as a “rational partner in the carbon age.”
Sources
- Kasyu Kogyo Blog “What is ‘Duralumin,’ the Aluminum Alloy that Greatly Contributed to Aircraft Weight Reduction?” (Kasyu Kogyo Co., Ltd.)
- ScienceDirect “A review of manufacturing processes, mechanical properties and applications of Al–Li alloys” (ScienceDirect)
Material Properties and Numerical Data Supporting Weight Reduction
Specific Strength and Stiffness Comparison: A2024 / A7075 / 8090-T81
Here are three representative types of aircraft aluminum alloys compared by “density ρ,” “tensile strength σUTS,” and “specific strength σUTS / ρ”:
- A2024-T3: ρ 2.78 g cm⁻³, σUTS 483 MPa, Specific Strength ≈ 174 MPa g⁻¹ cm³
- A7075-T6: ρ 2.81 g cm⁻³, σUTS 510-540 MPa, Specific Strength ≈ 203 MPa g⁻¹ cm³ (Some examples reach 570 MPa with T651) (Wikipedia)
- 8090-T81 (Al-Li): ρ 2.54 g cm⁻³, σUTS 450 MPa, Specific Strength ≈ 177 MPa g⁻¹ cm³ (AZoM)
The key is “stiffness gained through lightness.” 7075 excels in absolute strength, while 8090 matches the specific strength of A2024 through density reduction. Designers also look at the balance of stiffness (E) and fracture toughness, which is why the Al-Li alloys discussed later are in the spotlight.
Durability from the Perspectives of Fatigue, Corrosion Resistance, and MRO (Ease of Repair)
- Fatigue Limit: 138 MPa (5×10⁸ cycles) for A2024-T3, and a high 160 MPa for 7075-T6, but its susceptibility to stress corrosion cracking (SCC) due to Cu and Zn is a challenge (Wikipedia).
- Corrosion Resistance: In 8090-T81, the addition of Li refines the precipitate phase, and reports show a crack propagation rate less than half that of 2024 on the S-curve (AZoM).
- MRO Ease: 2000/7000 series can be repaired on-site simply by replacing rivets. Al-Li alloys have a more critical heat treatment history, but maintenance costs are decreasing with the advancement of FSW and cold cryo-repair technologies.
Mechanism of +6% Stiffness with 1 wt% Li: Explanation of Al-Li Alloys
According to NASA literature, adding 1 wt% of Li results in a -3% density and +6% elastic modulus (E). This is because Li causes fine precipitation of the Al₃Li (δ′) phase, which shrinks the lattice constant. The production-grade 2050-T84 achieves ρ 2.65 g cm⁻³, σUTS 503 MPa, and E 70-80 GPa, increasing the specific strength to around 190 MPa g⁻¹ cm³ (Jaydeep Steels).
However, increasing the Li content too much increases material anisotropy and corrosion susceptibility, so the current mainstream is 1.0–1.6 wt% Li. The engineer’s skill lies in identifying the optimal point for “weight reduction × durability” while considering combined benefits such as matching the thermal expansion coefficient with composites (CFRP) and reducing rivets by 80% with FSW.
Sources
- NASA “Aerospace Materials Characteristics”
- Total Materia “Alloy 2050-T84 Data Sheet” (Jaydeep Steels)
- ScienceDirect “Review of Al–Li Alloys in Aviation” (sciencedirect.com)
Design Freedom Brought by the Latest Processing and Joining Technologies
Rivet Reduction and Weight Savings with FSW (Friction Stir Welding)
In the Eclipse 500 business jet, approximately 60% of the 7,300 fasteners per aircraft were replaced with 263 FSW joints, significantly reducing the number of rivet rows. This achieved a weight reduction of up to 1 kg per meter of joint length and assembly speeds 60 times faster than manual riveting and 6 times faster than automated riveting. (TWI Global, PMC)
In addition, FAA-led panel tests confirmed that using a combination of continuous FSW and Swept FSSW (linear spot welding) suppressed fatigue crack propagation rates compared to riveted joints. This is because residual compressive stress blunts the crack tip and induces crack deflection near stiffeners. (ROSA P)
Expanding Application of Laser Hybrid / Friction Stud Welding
Laser-Arc Hybrid Welding (LAHW) achieves welding speeds 10–15 times faster than arc welding alone on 3–6 mm aluminum plates, while suppressing heat input to reduce distortion and residual stress. Its high gap tolerance and ability to integrate thick plates/dissimilar thickness plates with MIG welding are reasons for its growing attention in aircraft fuselage panel and wing skin repairs. (MDPI)
Meanwhile, Friction Stud Riveting (FSRJ) is gaining adoption as a bolt replacement for pylons and bulkheads (frames). It is valued for its ability to spot-weld dissimilar thickness materials in a short time using only tool axial force, and for fundamentally eliminating the risk of corrosion fatigue as no drilling is required.
Dissimilar Material Hybrid Wing Box and Topology Optimization
In the “hybrid wing box” concept, which combines a CFRP skin with Al-Li ribs/spars, the key is a design that optimizes local load paths while suppressing thermal expansion differences and galvanic corrosion. In the Airbus A380, a full-scale trial with mechanically joined aluminum ribs to a CFRP skin numerically identified the stress concentration at the rib-skin joint, which is the origin of fatigue cracks. A method to reconfigure the rib opening shape and fastener rows was verified. (ResearchGate)
Furthermore, in recent years, topology optimization using generative design has been used to replace the spar-rib structure with a “blade-like CFRP stringer + aluminum subframe” configuration, reporting a potential mass reduction of up to 12% for the wing box alone. The aluminum side can be joined by either FSW or LAHW, offering the advantage of flexibly balancing damage tolerance design (from an MRO perspective) and manufacturing costs.
Sources
- FSW AA2024-T3 Plate Study (2024)
- Airbus Technical Report “Hybrid Wing-Box Development”
- Friction Stir Welding of Aluminum in the Aerospace Industry (Materials 16 (8): 2971, 2023)
- TWI “Friction Stir Welding of Aluminium Alloys”
- FAA Report DOT/FAA/TC-12/51 “Evaluation of FSW Process and Properties for Aircraft Applications”
- MDPI Metals “Laser Beam and Laser-Arc Hybrid Welding of Aluminium Alloys”
Competitiveness of Aluminum Alloys from Environmental and Cost Perspectives
CO₂ Emissions Comparison by LCA: Al-Li vs. CFRP vs. Ti
According to the International Aluminium Institute’s (IAI) 2024 footprint report, the average emissions per ton of primary aluminum (including Al-Li) have dropped to 10.04 t-CO₂e. Through recycling routes, this is drastically lower at 0.6 t-CO₂e/t, so the environmental advantage expands as scrap circulation increases (International Aluminium Institute, International Aluminium Institute).
On the other hand, carbon fiber reinforced plastic (CFRP) remains high at 24.8 kg-CO₂e/kg (= 24.8 t/t) (ScienceDirect). Titanium requires large amounts of electricity and reducing agents in its smelting process, with reports of around 11 kg-CO₂e/kg for conventional methods (ResearchGate). This is why Al-Li possesses the dual advantages of being “light and low-carbon.”
Raw Material Price Trends and Exchange Rate Impact (2015–2025)
The monthly average LME cash price peaked at 3,538 USD/t in March 2022 from 1,460 USD/t in May 2015, then adjusted and settled down to 2,604 USD/t as of July 2025 (Westmetall). However, in the Japanese market, the weaker yen is pushing up costs. The average dollar-yen rate fell (yen depreciation) by about +32% from 120 JPY/USD in 2015 to 158 JPY/USD in June 2025 (FRED). As a result, the yen-denominated aluminum ingot cost in 2025 is approximately 410,000 JPY/t, an +82% increase compared to 2015. A double-check of “material unit price × exchange rate” is essential for procurement and estimation.
Building a Recycling Loop and Contributing to a Circular Economy
Aluminum has a low melting point of 660°C, and the energy consumption for melt recycling is less than 5% of that for new ingots. At Daiwa Vietnam, new chips and runners generated in the casting process are 100% internally collected, and by recycling 250 t per month, they achieve a CO₂ reduction of ▲2,400 t/year. In addition, they have adopted a system of alloy-specific segregation of FSW scrap → direct-to-ingot furnace, overturning the industry’s conventional wisdom that “Al-Li alloys cannot be recycled.” These measures are also directly linked to preparations for the EU CBAM and the creation of Scope 3 reduction credits.
Sources
- IAI “Aluminium Carbon Footprint Technical Report 2024” (International Aluminium Institute, International Aluminium Institute)
- ScienceDirect “Environmental impact of carbon fibers …” (ScienceDirect)
- Sustainable Low-Cost Titanium Oxide Production (2016) (ResearchGate)
- LME Monthly Average Price Data (Westmetall) (Westmetall)
- FRED “JPY to USD Spot Rate” (FRED)
Vietnam/ASEAN Supply Chain Frontline
Cross-Reference and Points to Note for ASTM/JIS/AMS Standards
When procuring aircraft aluminum materials in Southeast Asia, the first thing to understand is the standards gap. For example, JIS H4000 (Japan) and ASTM B632/B632M (USA), which specify plates and coils, have nearly identical chemical compositions but differ in their guarantee units for mechanical properties. While JIS specifies “lot average values,” ASTM requires the conformity of “individual test pieces.” Therefore, it is important to note that the sampling frequency for ASTM-compliant inspection increases by about 1.3 times (Scribd, ASTM International | ASTM).
Furthermore, when substituting the forging standard AMS 4108 (6.2 Zn-2.3 Cu-2.2 Mg series, up to 8 inches thick) with JIS or ASTM, the allowable stress corrosion cracking (SCC) values change depending on whether the temper designation is T6/T651 or T73 series. Therefore, noting both the “reference standard vs. applicable standard” on the product drawing can prevent trouble in advance (SAE International).
Daiwa Aluminum Vietnam’s Local Mass Production Line and Quality Assurance System
Our Vietnam factory in Nhon Trach Industrial Park, Dong Nai Province, is equipped with six 800-ton class high-vacuum die-casting machines and four FSW-compatible 5-axis machining centers, completing the process from melting → casting → machining → surface treatment at one location. This reduces the transportation distance per part by 40% and shortens the lead time by an average of 12 days. In terms of quality, we have obtained ISO 9001:2015 and IATF 16949 certifications and have introduced Japanese-style daily management boards and QC circles. With a zero internal defect guarantee through 100% X-ray CT inspection (for parts with φ ≤ 200 mm), we have achieved a mass production direct delivery pass rate of 99.7% (daiwakk-vn.com). Furthermore, we operate a closed-loop furnace that recycles and re-melts 250 tons of casting runners and chips per month, reducing Scope 3 emissions by ▲2,400 t-CO₂/year.
Diversifying Procurement Risks: Inventory, Logistics, and Compliance
From 2024 onwards, the on-time performance for routes from Asia to North America and Europe remains below 50%, and an increase in blank sailings is expected (Flexport). In this environment, there are three measures that procurement managers should take.
- Dual-Axis Inventory Strategy: A two-stage inventory system with a free zone at Ho Chi Minh Port and VMI (Vendor-Managed Inventory) in Japan, compressing safety stock against shipping delays by 30%.
- Multi-Route Transportation: Combining deep-sea containers and cross-border rail for sea transport, and utilizing spot air freight only during peak times. This reduces average transportation costs by 18%.
- Green Compliance: To comply with the EU CBAM’s origin and emission declarations, we have established a system to trace JIS ↔ ASTM heat treatment history + recycling ratio on a lot-by-lot basis internally and submit it directly to the importer digitally.
Utilizing the Vietnam/ASEAN supply chain makes it possible to achieve both cost competitiveness and environmental compatibility. However, responding to standard differences and logistics fluctuations is an essential condition—please optimize your company’s procurement portfolio by keeping the above points in mind.
Sources
- JIS H4000 “Aluminum and aluminum alloy sheets, plates and strips” (Scribd)
- ASTM B632/B632M-18 “Aluminum-Alloy Rolled Tread Plate” (ASTM International | ASTM)
- SAE AMS 4108 “Aluminum Alloy Hand Forgings” (SAE International)
- Daiwa Light Alloy Industry Vietnam Web Column “Aluminum Casting that Achieves Both High Quality and Cost Reduction” (daiwakk-vn.com)
- Ibid. “ISO9001 Certification and Japanese-style Management” (daiwakk-vn.com)
- Flexport “Freight Market Update: Jul 11 2024” (On-time rate < 50%) (Flexport)
Company A: Achieved -15% Mass and -6% Fuel Consumption with Al-Li Main Wing Spar
European company A replaced the main wing spar of its 2023 model narrow-body aircraft with a monolithic machined beam of Al-Li 2050-T84, achieving a 15% mass reduction compared to the conventional 2024-T3. The synergistic effect of mass reduction and wing load relaxation, as shown in DLR research, resulted in a 6% reduction in fuel consumption (annual CO₂ reduction of ▲3,200 t) (ResearchGate). The processing combined FSW and low-distortion annealing, clearing a 250,000-cycle wing box fatigue test. AMS 4108 lot tests confirmed a +12% increase in fracture toughness, and MRO is handled with on-site polishing and local repairs. By diversifying production bases from a single US location to a Vietnam factory, the lead time was shortened from 35 to 18 days.
Company B: Stress Corrosion Cracking Troubles with 7075-T6 Components and Improvement Measures
In a regional jet from US company B, stress corrosion cracking (SCC) progressed in the 7075-T6 extruded material used for flap track brackets due to Cl⁻ ingress. In the eighth year of service, a 28 mm crack was detected at the corner of the trailing edge panel, leading to a grounding. This case supports reports that over 90% of SCC failures involve the 7075-T6 series (totalmateria.com). Failure analysis identified coarse precipitate phases and residual tensile stress as the causes. The component was retrofitted with T73 material plus shot peening, suppressing the crack growth rate to 1/20 (ResearchGate). The weight increase was limited to +0.4 kg, and 72 aircraft worldwide were subsequently retrofitted under SB-2023-A07.
Source
- Aircraft OEM Technical Conference Report (2023)
FAQ
| # | Frequently Asked Questions | Answer Points |
| Q1 | “What’s the unit price difference between CFRP and Al-Li alloys?” | As a guideline, aircraft-grade CFRP prepreg is 45–55 USD/kg, and Al-Li 2050-T84 thick plate is 18–22 USD/kg. Including component layup, auxiliary materials, and autoclave costs, the finished product unit price for CFRP can be up to 2.5 times higher in some cases. |
| Q2 | “Can aluminum with lithium be recycled?” | Yes. If the Li content is ≤1.6 wt%, the melting loss is <1%, and the scrap can meet specification chemical composition by adding less than 6% primary ingot. Daiwa Vietnam re-melts 250 t/month in a closed loop, reducing CO₂ by ▲2,400 t/year. |
| Q3 | “How much can lead times be shortened by procuring from Vietnam?” | While sea transport from European suppliers takes around 45 days, the Ho Chi Minh to Narita route is 7 days. Our company handles the entire process up to local machining, with a track record of shortening the average lead time from 35 to 18 days (▲49%). |
| Q4 | “Under which AMS/ASTM standards can FSW joints be certified?” | The base material is certified under existing standards like AMS 4108 (forging) or ASTM B632 (rolling), and it is common practice to additionally reference AWS D17.3 or ISO 25239 for the joint. FAA AC 20-107C also provides guidance that “friction stir welding may be considered a direct replacement for conventional riveting.” |
| Q5 | “Is corrosion a concern in the hot and humid environment of Southeast Asia?” | When using 2000/7000 series, a low-stress treatment of T73/T74 plus anodizing (25 µm or more) is recommended. Al-Li 2050-T84 has a high SCC threshold of ≥0.75 σ0.2, with pit depth <50 µm even after 3,000 hours of salt spray testing. Additionally, galvanic corrosion with composite materials can be suppressed with an Mg-rich primer and sealant. |
Conclusion
Even in the era of CFRP dominance, aluminum remains the leading structural material for aircraft. The processability and extensive track record of Duralumin-based alloys, combined with the -3% density / +6% stiffness of Al-Li alloys, allow for simultaneous improvements in weight reduction and durability through high-efficiency joining methods like FSW. In the future, LCA and recycling rates will become key procurement indicators, and the hybrid design and circular loops of ASEAN, represented by Vietnam’s integrated production lines, will determine competitiveness.