Duralumin

Cross-sectional reinforcement of duraluminium affected by the Hindenburg airship fire, recovered from its fall site at McGuire Air Base, New Jersey on May 6, 1937.

Duralumin is an alloy of aluminum with copper, manganese, magnesium and silicon. They belong to the family of aluminum-copper alloys (1998).

Contrary to what it might seem, the name duralumin does not come from "hard aluminum", but from Düren, the German city where Alfred Wilm first manufactured this alloy in 1909.

Today, the term primarily refers to aluminum and copper alloys, designated as the 2000 series by the International Alloy Designation System (IADS), as well as the 2014 and 2024 alloys used in the manufacture of fuselages.

It has a high mechanical resistance at room temperature, but its resistance to corrosion, weldability and aptitude for anodizing are low. They are used in the aeronautical and automobile industries. It has an elastic limit of about 450 MPa, a value that varies according to the composition and tempering.

Discovery

In 1906 the German Alfred Wilm developed the first exclusively forged alloy as part of research to increase the strength of aluminum alloys. His discovery was to increase the hardness of the alloy by transferring the methods used in steel production to increase the strength of an aluminum alloy. Alloy samples left for a few days after quenching were found to show higher strength. The underlying principle is known as precipitation hardening.

The new material was manufactured by the Düren metallurgy starting in 1909 and the name Duralumin and some similar ones (DURAL) are protected as registered trademarks. Wilm's aluminum alloy, 3.5 to 5.5 percent copper, 0.5 to 0.8 percent magnesium, and 0.6 percent manganese, as well as up to 1 percent silicon and 1.2 percent iron has also been filed for a patent. The name is derived from the Latin durus for 'hard'; (or better: "persevering" in the sense of constant, resistant), although in the literature there is an occasional connection with the Düren workplace as well as the main component of aluminum alloy. Today there are numerous comparable alloys that have added the manufacturer's name to the alloy designation.

Corrosion protection

Although the addition of copper improves strength, it also makes these alloys susceptible to corrosion. For sheet products, corrosion resistance can be greatly improved by metallurgical bonding of a high purity aluminum surface layer. These sheets are called alclad and are commonly used in the aircraft industry.

Uses and applications

Aluminum alloyed with copper (Al-Cu alloys), which can be hardened by precipitation, is designated by the International Alloy Designation System as the 2000 series. It is one of the most widely used alloys, within aluminum, Allowing for applications hitherto reserved for steels, typical uses for wrought Al-Cu alloys include:

• Tornillery.
• Automotive.
• Blow molds.
• Mosquetons.
• Prints.
• Utensils.

Uses in aviation

Hardness sample used in the USS airlock Akron (1931).

The first plane manufactured on a massive scale that used large-scale duraluminium was the Junkers J.I sesquiplane of the First World War.

Due to the improved material properties, the replacement of steel by an aluminum alloy in aviation and weapons technology became significant in the first place. Earlier alloys, such as zinc-aluminum alloys, were significantly more susceptible to stress corrosion cracking and did not achieve the required strength anywhere near.

The first mass-produced aircraft to make extensive use of duralumin, the Junkers JI armored sesquiplane of World War I. German scientific literature openly published information about duralumin, its composition and heat treatment, before the outbreak of the World War I in 1914. Despite this, use of the alloy outside of Germany did not occur until after the fighting ended in 1918. Reports of German use during World War I, even in technical journals such as Flight, still it could misidentify its key alloy component as magnesium rather than copper. UK engineers showed little interest in duralumin until after the war.

The first known attempt to use duralumin for a heavier-than-air airframe occurred in 1916, when Hugo Junkers first introduced its use in the Junkers J 3 airframe a "technology demonstrator" 3. 4; single-engine monoplane that marked the first use of the Junkers brand corrugated duralumin skin. The Junkers company completed only the covered wings and tubular fuselage frame of the J 3 before abandoning development. The slightly later Junkers J.I armored sesquiplane, designated only IdFlieg of 1917, known at the factory as the Junkers J 4, had its all-metal wings and its horizontal stabilizer fabricated in the same way as the wings. from the J 3, such as the experimental duralumin Junkers J 7 single-seat fighter and airworthy design, which led to the Junkers D.I low-wing monoplane fighter, introducing all-duralumin aircraft structural technology to German military aviation in 1918.

Its first use in airframes was in rigid airship frames that eventually included all of the "Big Airship" from the 1920s and 1930s: the British-made R-100, the German passenger Zeppelins Graf Zeppelin LZ 127 LZ 129 Hindenburg, LZ 130 Graf Zeppelin, and the United States Navy airships USS Los Angeles (ZR- 3) USS Akron (ZRS-4) and USS Macon (ZRS-5).

Uses in cycling

Duralumin was used to make bicycle frames and components from the 1930s to the 1990s. Several companies in Saint-Étienne, France were noted for their early and innovative adoption of duralumin: in 1932, Verot et Perrin they developed the first light alloy connecting rods; in 1934 Haubtmann released a complete crankset; Beginning in 1935, various companies made duralumin freewheels, derailleurs, pedals, brakes, and handlebars.

Full framesets quickly followed, including those made by: Mercier (and Aviac and other licensees) with their popular family of Meca Dural models, the Pelissier brothers and their race-worthy La Perle models, and Nicolas Barra and his exquisite mid-century XX. Other names that crop up here as well were: Pierre Caminade, with his beautiful Caminargent creations and exotic octagonal tubing, and also Gnome et Rhône, with its deep heritage as an aircraft engine manufacturer that also branched out into motorcycles, mopeds and bicycles after the World War.

Mitsubishi Heavy Industries, which was banned from producing aircraft during the US occupation of Japan, made the "cross" with duralumin left over from the war in 1946. The "cross" it was designed by Kiro Honjo, a former aircraft designer responsible for the Mitsubishi G4M.

The use of duralumin in bicycle manufacturing faded in the 1970s and 1980s. However, the Vitus bicycle company released the venerable “979” frame in 1979, a “Duralinox” model that became a Instant classic among bikers. The Vitus 979 was the first production aluminum frameset whose thin-walled 5083/5086 tubing was slipped on and then glued down with a dry, heat-activated epoxy. The result was an extremely light yet highly durable frame. Production of the Vitus 979 continued until 1992.

Other uses

Before heat treatment, the alloy is ductile and malleable. After heat treatment, a reaction between aluminum and magnesium causes an increase in hardness and tensile strength.

Duralumin has high mechanical strength at room temperature, however, its oxidation resistance, weldability, and suitability for anodizing are poor. They are used in the aeronautical and automobile industry.

• 2011: Wing, rod and rod for screw machine products. Applications where good machinability and good resistance are required.
• 2014: Parts forged heavy duty plates and extrusions for aircraft accessories, wheels and main structural components, tank and spatial reinforcement structure, truck rack and suspension components. Applications that require high strength and hardness, including service at high temperatures.
• 2017 or Avional (France): About 1% Yes. Good machinability. Resistance acceptable to air corrosion and mechanical properties. Also called AU4G in France. Used for aircraft applications between wars in France and Italy. It was also used in motor racing applications from the 1960s, as it is a tolerant alloy that could be pressurized with relatively little sophisticated equipment.
• 2024: Aircraft structures, rivets, hardware, truck wheels, screw machine products and other structural applications.
• 2036: Chapa for body panels.
• 2048: Chapa and plate in structural components for aerospace applications and military equipment.

Note: The numbers indicate the Duraluminium alloy, the different series can be differentiated by the alloys they have, their proportion, and the heat treatments or other types used to obtain them.

Main properties

Alloy with very high characteristics and tensile strength, very high mechanical resistance at room temperature, however, its resistance to corrosion, weldability and aptitude for anodizing are low. They are used in the aeronautical and automotive industries.

• Good machining.
• Poca resistance to abrasion.
• Poca resistance to corrosion.