# Duralumin
**Duralumin** is the trade name of one of the earliest age-hardenable aluminum alloys, an aluminum alloy containing roughly 4% copper with smaller additions of magnesium and manganese, whose strength develops after solution treatment and aging through the precipitation of nanoscale Cu-Mg-rich phases.[1](https://www.sciencedirect.com/science/article/pii/S258915291930225X) It was discovered in 1906 by the German metallurgist Alfred Wilm, marketed from 1909 under a name combining hardness and the town of Düren, and it triggered the development of all-metal aviation at the beginning of the twentieth century.[1](https://www.sciencedirect.com/science/article/pii/S258915291930225X) • [2](https://www.chemistryworld.com/opinion/alfred-wilm-and-the-hardening-of-metals/4023249.article)
| Key fact | Detail |
|---|---|
| Discovery | Age hardening found by Alfred Wilm in 1906 during systematic alloy research at a Prussian military laboratory near Berlin[3](https://www.jstage.jst.go.jp/article/matertrans/64/2/64_MT-LA2022019/_html/-char/en) |
| Patent | Application filed January 11, 1907 for an alloy with not more than 2% Mg and not more than 5% Cu, especially effective with 4% Cu and 0.25–0.5% Mg (DRP204543, approved November 1908)[3](https://www.jstage.jst.go.jp/article/matertrans/64/2/64_MT-LA2022019/_html/-char/en) |
| Original composition | Close to 4 Cu–0.7 Mg–0.6 Mn–0.6 Si wt%; first productions contained 3 to 5.6% copper and 0.5% magnesium[1](https://www.sciencedirect.com/science/article/pii/S258915291930225X) • [4](https://stm.cairn.info/revue-cahiers-d-histoire-de-l-aluminium-2015-1-page-82?lang=fr) |
| Strengthening mechanism | Precipitation sequence from supersaturated solid solution through GPB zones toward the equilibrium S phase (Al2CuMg)[5](https://www.sciencedirect.com/science/article/abs/pii/S1359646205005397) |
| Modern descendant | Alloy 2024 (Cu 3.8–4.9%, Mg 1.2–1.8%, Mn 0.30–0.9%); 2024-T3 sheet has a tensile strength of 450 MPa and yield strength of 310 MPa[6](https://unitedaluminum.com/aluminum-technical-data-alloy-chemistry-and-mechanical/) • [7](https://materialsdata.nist.gov/bitstream/handle/11115/176/Aluminum%20Campbell.pdf) |
| Aviation landmark | The Junkers F.13 of 1919, the first all-metal commercial aircraft, was constructed largely of duralumin[8](https://collection.sciencemuseumgroup.org.uk/objects/co29251/model-of-junkers-f-13-all-metal-transport-aeroplane) |
## Discovery by Alfred Wilm
The Prussian engineer Alfred Wilm (1869–1937) had been mandated at a military laboratory in Neubabelsberg near Berlin to develop an improved aluminum alloy for munitions, work that began systematically in the early 1900s.[9](https://doi.org/10.1051/metal%3A2004157) • [3](https://www.jstage.jst.go.jp/article/matertrans/64/2/64_MT-LA2022019/_html/-char/en) According to one account, on a Saturday in September 1906 Wilm added half a percent of magnesium to a batch of Al-Cu-Mn alloy; when his assistant Musehold repeated the hardness measurement on the Monday, the metal had become seriously hard, a result so striking that Wilm suspected the instrument had been tampered with.[2](https://www.chemistryworld.com/opinion/alfred-wilm-and-the-hardening-of-metals/4023249.article) Repeated experiments confirmed that the metal changed over hours at room temperature, and that hardening by heating and aging worked for alloys but not for pure materials.[2](https://www.chemistryworld.com/opinion/alfred-wilm-and-the-hardening-of-metals/4023249.article)
On January 11, 1907, Wilm applied for a patent covering an aluminum alloy with no more than 2% Mg and no more than 5% Cu, which worked best at 4% Cu and 0.25–0.5% Mg; the grant, DRP204543, came through in November 1908.[3](https://www.jstage.jst.go.jp/article/matertrans/64/2/64_MT-LA2022019/_html/-char/en) In 1909, after leaving his employer, he licensed the patent to a foundry in Düren, Westphalia, which marketed the metal under the name Duralumin, a half-pun implying both hardness (Latin *dur*) and the town of Düren; Wilm himself had first suggested the name Hartaluminium, using the German word for hard.[2](https://www.chemistryworld.com/opinion/alfred-wilm-and-the-hardening-of-metals/4023249.article) • [3](https://www.jstage.jst.go.jp/article/matertrans/64/2/64_MT-LA2022019/_html/-char/en) The name is attributed both to the alloy's hardness and to its first industrial production in Düren.[9](https://doi.org/10.1051/metal%3A2004157) The English company Vickers bought the rights and conducted its own alloy research, concluding that a silicon impurity, which the German producers kept quiet, was critical to the change in properties.[2](https://www.chemistryworld.com/opinion/alfred-wilm-and-the-hardening-of-metals/4023249.article)
## Why it hardens: the precipitation sequence
The hardening that Wilm observed remained unexplained for years. Two studies published by the US National Bureau of Standards in 1919, building on the theory of [Paul Dyer Merica](https://www.edgepedia.org/paul-dyer-merica) and colleagues, applied phase diagrams to the phenomenon and concluded that age hardening of aluminum was a room-temperature precipitation phenomenon; Merica's theory identified the hardening constituent as CuAl2 and tied the hardening effect to particle size.[10](https://nvlpubs.nist.gov/nistpubs/sp958-lide/014-015.pdf) Almost 20 years passed before the responsible precipitates were detected experimentally by small-angle x-ray scattering and became known as Guinier-Preston (GP) zones.[10](https://nvlpubs.nist.gov/nistpubs/sp958-lide/014-015.pdf)
In Al-Cu-Mg alloys of duralumin type, where copper and magnesium are present in comparable amounts, the strengthening precipitates belong to the S-phase family rather than the CuAl2 (θ) family. Bagaryatsky proposed the sequence supersaturated solid solution → GPB zone → S″ → S′ → S, where S is the equilibrium CuMgAl2 (Al2CuMg) phase.[5](https://www.sciencedirect.com/science/article/abs/pii/S1359646205005397) A 2005 critical review by S. C. Wang and M. J. Starink, materials scientists at the [University of Southampton](https://www.edgepedia.org/university-of-southampton), found evidence for only two truly distinct pre-precipitates and represented the sequence as supersaturated solid solution → co-clusters → GPB2/S″ → S, with the Cu-Mg co-clusters (also termed GPB or GPB I zones) forming within a short time of aging and the orthorhombic, matrix-coherent GPB2/S″ phase having the probable composition Al10Cu3Mg3.[11](https://journals.sagepub.com/doi/10.1179/174328005X14357) The complete sequence is still debated; a transient nonequilibrium GPB2/S″ phase is the main point of controversy.[12](https://pmc.ncbi.nlm.nih.gov/articles/PMC5876935/)
Hardening proceeds in two stages: the rapid formation of Mg-Cu co-clusters accounts for the initial age hardening, while the second stage is dominated by the S phase, which forms a dense precipitate structure at peak hardness.[12](https://pmc.ncbi.nlm.nih.gov/articles/PMC5876935/) • [5](https://www.sciencedirect.com/science/article/abs/pii/S1359646205005397) [High-resolution transmission electron microscopy](https://www.edgepedia.org/high-resolution-transmission-electron-microscopy) of an alloy aged at 250 °C showed GPB zones as fine rod-like features on the {012} Al planes after 0.5 h, diminishing as S′ precipitates became predominant after about 2 h, with crystallographic continuity indicating that GPB zones act as precursors for S′ nucleation and thickening.[13](https://www.mdpi.com/2504-4494/10/4/129)
## Modern descendants
Duralumin's composition corresponds to what became the 2xxx series of heat-treatable wrought aluminum alloys. Alcoa commercialized alloy 17S (Al–4.0%Cu–0.6%Mg–0.7%Mn), similar to Duralumin, with a tensile strength of 425 MPa and yield strength of 275 MPa.[3](https://www.jstage.jst.go.jp/article/matertrans/64/2/64_MT-LA2022019/_html/-char/en) The modern alloy 2017 is similar to original Duralumin, and alloy 2024, with registered composition limits of 3.8–4.9% Cu, 1.2–1.8% Mg, and 0.30–0.9% Mn, is the widely used high-strength aerospace alloy of this family.[14](https://www.govinfo.gov/content/pkg/GOVPUB-SI-PURL-gpo175106/pdf/GOVPUB-SI-PURL-gpo175106.pdf) • [6](https://unitedaluminum.com/aluminum-technical-data-alloy-chemistry-and-mechanical/) In the T3 temper as sheet or plate, 2024 has a tensile strength of 450 MPa (65 ksi), a yield strength of 310 MPa (45 ksi), and 18% elongation in 50 mm.[7](https://materialsdata.nist.gov/bitstream/handle/11115/176/Aluminum%20Campbell.pdf)
**Corrosion protection.** Copper-containing alloys of this type have poor natural corrosion resistance, so 2024 sheet is often produced as Alclad, a composite in which thin layers of aluminum alloy 1230 (99.30% minimum aluminum), anodic to the core, are metallurgically bonded to both surfaces.[15](https://saemobilus.sae.org/standards/amsqqa2505c-aluminum-alloy-alclad-2024-plate-sheet) Because the cladding is anodic to the core, it dissolves preferentially and protects the core electrochemically; in 20-year atmospheric exposure tests, alclad 2024 retained its mechanical properties and the cladding was not penetrated by pitting.[16](https://www.sciencedirect.com/science/article/abs/pii/S0010938X09000407)
## Role in early aviation
Duralumin arrived as aircraft construction was abandoning wood and fabric. The German designer [Hugo Junkers](https://www.edgepedia.org/hugo-junkers) used it for the Junkers F.13, conceived in 1918 and first flown in 1919, which was the first all-metal commercial aircraft; it carried two crew and four passengers, was constructed largely of duralumin, and served as the prototype of later generations of airliners.[8](https://collection.sciencemuseumgroup.org.uk/objects/co29251/model-of-junkers-f-13-all-metal-transport-aeroplane) • [17](https://www.aopa.org/news-and-media/all-news/2019/april/11/the-new-junkers-f13) A contemporary American description of the F 13 gives the alloy as containing 95% aluminum, 4% copper, 0.5% manganese, and 0.5% magnesium.[18](https://digital.library.unt.edu/ark%3A/67531/metadc57541/m1/4/) The alloy was also marketed as a replacement for wood, magnesium, and even some carbon steels in Zeppelins.[2](https://www.chemistryworld.com/opinion/alfred-wilm-and-the-hardening-of-metals/4023249.article)
## References
1. [Precipitation in original Duralumin A-U4G versus modern 2017A alloy, ScienceDirect](https://www.sciencedirect.com/science/article/pii/S258915291930225X)
2. [Alfred Wilm and the hardening of metals, Chemistry World](https://www.chemistryworld.com/opinion/alfred-wilm-and-the-hardening-of-metals/4023249.article)
3. [History of the Development of Extra Super Duralumin and Future Research Issues of Al–Zn–Mg Alloys, Materials Transactions 64 (2023)](https://www.jstage.jst.go.jp/article/matertrans/64/2/64_MT-LA2022019/_html/-char/en)
4. [Un alliage incontournable aux débuts de l'aéronautique : le Duralumin, Cahiers d'histoire de l'aluminium (2015)](https://stm.cairn.info/revue-cahiers-d-histoire-de-l-aluminium-2015-1-page-82?lang=fr)
5. [Precipitation hardening in Al–Cu–Mg alloys revisited, Scripta Materialia 54 (2006)](https://www.sciencedirect.com/science/article/abs/pii/S1359646205005397)
6. [Aluminum Alloy Chemistry and Mechanical Data, United Aluminum](https://unitedaluminum.com/aluminum-technical-data-alloy-chemistry-and-mechanical/)
7. [Elements of Metallurgy and Engineering Alloys, ASM/NIST](https://materialsdata.nist.gov/bitstream/handle/11115/176/Aluminum%20Campbell.pdf)
8. [Model of Junkers F.13 all-metal Transport Aeroplane, Science Museum Group Collection](https://collection.sciencemuseumgroup.org.uk/objects/co29251/model-of-junkers-f-13-all-metal-transport-aeroplane)
9. [O. Hardouin Duparc, Alfred Wilm and the beginnings of Duralumin, Revue de Métallurgie 101 (2004)](https://doi.org/10.1051/metal%3A2004157)
10. [A Century of Excellence in Measurements, Standards, and Technology, NIST](https://nvlpubs.nist.gov/nistpubs/sp958-lide/014-015.pdf)
11. [S. C. Wang and M. J. Starink, Precipitates and intermetallic phases in precipitation hardening Al–Cu–Mg–(Li) based alloys, International Materials Reviews 50 (2005)](https://journals.sagepub.com/doi/10.1179/174328005X14357)
12. [In Situ Structural Characterization of Ageing Kinetics in Aluminum Alloy 2024, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC5876935/)
13. [Insights into GPB Zones Evolution and S′ Phase Formation in Al-Cu-Mg Alloy, MDPI (2025)](https://www.mdpi.com/2504-4494/10/4/129)
14. [Among the first heat-treatable aluminum alloys was Duralumin, US Government Publishing Office](https://www.govinfo.gov/content/pkg/GOVPUB-SI-PURL-gpo175106/pdf/GOVPUB-SI-PURL-gpo175106.pdf)
15. [AMSQQA250/5C: Aluminum Alloy Alclad 2024, Plate and Sheet, SAE International](https://saemobilus.sae.org/standards/amsqqa2505c-aluminum-alloy-alclad-2024-plate-sheet)
16. [Long-term atmospheric corrosion behaviour of aluminium alloys 2024 and 7075, Corrosion Science 51 (2009)](https://www.sciencedirect.com/science/article/abs/pii/S0010938X09000407)
17. [The 'new' Junkers F 13, AOPA (2019)](https://www.aopa.org/news-and-media/all-news/2019/april/11/the-new-junkers-f13)
18. [All-Metal Junkers Airplane, Type F 13, UNT Digital Library](https://digital.library.unt.edu/ark%3A/67531/metadc57541/m1/4/)
19. [Junkers F-13 CF-ALX, Royal Aviation Museum of Western Canada](https://www.royalaviationmuseum.com/aircraft/junkers-f-13-cf-alx/)
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*Topic: Encyclopedia › Technology and the built world › Engineering and manufacturing › Materials science and metallurgy › Metal alloys and steels › Titles 1 to In*
*Initially written Sep 17, 2026 · Reviewed: Oct 15, 2026 · Edited: Oct 15, 2026 · Last review: Oct 15, 2026*
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