Duralumin (also calledduraluminum,duraluminium,duralum,dural(l)ium, ordural) is a trade name for one of the earliest types ofage-hardenablealuminium–copper alloys. The term is a combination ofDüren andaluminium[citation needed]. Its use as a trade name is obsolete. Today the term mainly refers to aluminium-copper alloys, designated as the 2000 series by the international alloy designation system (IADS), as with2014 and2024 alloys used in airframe fabrication.
Duralumin was developed in 1909 in Germany.Duralumin is known for its strength and hardness, making it suitable for various applications, especially in the aviation and aerospace industry. However, it is susceptible to corrosion, which can be mitigated by using alclad-duralum materials.
Duralumin was developed by the German metallurgistAlfred Wilm at private military-industrial laboratoryZentralstelle für wissenschaftlich-technische Untersuchungen [de] (Center for Scientific-Technical Research) inNeubabelsberg. In 1903, Wilm discovered that afterquenching, analuminium alloy containing 4% copper would harden when left at room temperature for several days. Further improvements led to the introduction of duralumin in 1909.[1] The name,originally a trade mark of Dürener MetallwerkeAG which acquired Wilm's patents and commercialized the material, is mainly used inpop-science to describe allAl-Cu alloys system, or '2000' series, as designated through the international alloy designation system originally created in 1970 by theAluminum Association.
In addition toaluminium, the main materials in duralumin arecopper,manganese andmagnesium. For instance, Duraluminium 2024 consists of 91-95% aluminium, 3.8-4.9% copper, 1.2-1.8% magnesium, 0.3-0.9% manganese, <0.5% iron, <0.5% silicon, <0.25% zinc, <0.15% titanium, <0.10% chromium and no more than 0.15% of other elements together.[2] Although the addition of copper improves strength, it also makes these alloys susceptible tocorrosion. Corrosion resistance can be greatly enhanced by the metallurgical bonding of a high-purity aluminium surface layer, referred to asalclad-duralum.Alclad materials are commonly used in the aircraft industry to this day.[3][4]
Duralumin's remarkable strength and durability stem from its unique microstructure, which is significantly influenced by heat treatment processes.
Solid Solution: After initial solidification, duralumin exists as a single-phase solid solution, primarily composed of aluminium atoms with dispersed copper, magnesium, and other alloying elements. This initial state is relatively soft and ductile.
Solution annealing: Duralumin undergoes solution annealing, a high-temperature heat treatment process that dissolves the alloying elements into the aluminium matrix, creating a homogeneous solid solution.
Quenching: Rapid cooling (quenching) after solution annealing freezes the high-temperature solid solution, preventing the precipitation of strengthening phases.
Aging (precipitation hardening): During aging, the supersaturated solid solution becomes unstable. Fine precipitates, such as CuAl2 and Mg2Si, form within the aluminum matrix. These precipitates act as obstacles to dislocation movement, significantly increasing the alloy's strength and hardness.
The final microstructure of duralumin consists of a predominantly aluminium matrix dispersed fine precipitates (CuAl2, Mg2Si)grain boundaries. The size, distribution, and type of precipitates play a crucial role in determining the mechanical properties of duralumin. Optimal aging conditions lead to the formation of finely dispersed precipitates, resulting in peak strength and hardness.
Aluminium alloyed with copper (AlCu alloys), which can beprecipitation hardened, are designated by the International Alloy Designation System as the 2000 series. Typical uses forwrought AlCu alloys include:[5]
German scientific literature openly published information about duralumin, its composition and heat treatment, before the outbreak ofWorld War I in 1914. Despite this, use of the alloy outside Germany did not occur until after fighting ended in 1918. Reports of German use during World War I, even in technical journals such asFlight, could still mis-identify its key alloying component as magnesium rather than copper.[9] Engineers in the UK showed little interest in duralumin until after the war.[10]
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The earliest known attempt to use duralumin for a heavier-than-air aircraft structure occurred in 1916, whenHugo Junkers first introduced its use in the airframe of theJunkers J 3, a single-engined monoplane "technology demonstrator" that marked the first use of the Junkers trademark duralumin corrugated skinning. TheJunkers company completed only the covered wings and tubular fuselage framework of the J 3 before abandoning its development. The slightly later, solelyIdFlieg-designatedJunkers J.I armouredsesquiplane of 1917, known to the factory as the Junkers J 4, had its all-metal wings and horizontal stabilizer made in the same manner as the J 3's wings had been, like the experimental and airworthy all-duraluminJunkers J 7 single-seat fighter design, which led to theJunkers D.I low-wing monoplane fighter, introducing all-duralumin aircraft structural technology to German military aviation in 1918.
Its first use inaerostatic airframes came in rigidairship frames, eventually including all those of the "Great Airship" era of the 1920s and 1930s: the British-builtR100, the German passenger ZeppelinsLZ 127Graf Zeppelin,LZ 129Hindenburg,LZ 130Graf Zeppelin II, and theU.S. Navy airshipsUSSLos Angeles (ZR-3, ex-LZ 126),USSAkron (ZRS-4) andUSSMacon (ZRS-5).[11][12]
Duralumin was used to manufacture bicycle components and framesets from the 1930s to 1990s. Several companies in Saint-Étienne, France, stood out for their early, innovative adoption of duralumin: in 1932, Verot et Perrin developed the first light alloy crank arms; in 1934, Haubtmann released a complete crankset; from 1935 on, Duralumin freewheels,derailleurs, pedals, brakes and handlebars were manufactured by several companies.
Complete framesets followed quickly, including those manufactured by: Mercier (and Aviac and other licensees) with their popular Meca Dural family of models, the Pelissier brothers and their race-worthy La Perle models, and Nicolas Barra and his exquisite mid-twentieth century "Barralumin" creations. Other names that come up here also included: Pierre Caminade, with his beautiful Caminargent creations and their exotic octagonal tubing, and alsoGnome et Rhône, with its deep heritage as an aircraft engine manufacturer that also diversified into motorcycles, velomotors and bicycles after World War Two.
Mitsubishi Heavy Industries, which was prohibited from producing aircraft during the American occupation of Japan, manufactured the "cross" bicycle out of surplus wartime duralumin in 1946. The "cross" was designed byKiro Honjo, a former aircraft designer responsible for theMitsubishi G4M.[13]
Duralumin use in bicycle manufacturing faded in the 1970s and 1980s.Vitus nonetheless released the venerable "979" frameset in 1979, a "Duralinox" model that became an instant classic among cyclists. The Vitus 979 was the first production aluminium frameset whose thin-wall 5083/5086 tubing was slip-fit and then glued together using a dry heat-activated epoxy. The result was an extremely lightweight but very durable frameset. Production of the Vitus 979 continued until 1992.[14]
In 2011,BBS Automotive made the RI-D, the world's first production automobile wheel made of duralumin.[15] The company has since made other wheels of duralumin also, such as the RZ-D.[16]
Duralumin was used to manufacture bicycle components and framesets from the 1930s to 1990s.
