Duralumin

Duralumin ( ium ), is an aluminum alloy, which opened a new era for aluminum, especially when compared with pure aluminum by the resulting high strength and hardness.

Development

1906 developed Alfred Wilm in studies to increase the strength of aluminum alloys, the first exclusive wrought. His discovery was to increase the hardness of the alloy by the fact that you transferred the commonly used in steel making process to increase the strength of an aluminum alloy. It was found that the alloy samples was allowed to occur after the quenching, a few days, actually had an increased strength. The underlying principle is known as precipitation hardening.

The new material was produced in 1909 by the Duerener metal works and the name Duralumin protected together with some similar ( Dural ) as trademarks. Wilms alloy of aluminum, 3.5 to 5.5 percent copper, 0.5 to 0.8 percent and 0.6 percent manganese and magnesium up to 1% silicon and 1.2% iron was also applied for a patent. The name was derived from the Latin durus for " hard" (or better: " persevering " in the sense of proof, resistant ), in the literature sometimes a relationship is described to work Düren, as well as the main constituent of the alloy aluminum. Meanwhile, there are numerous similar alloys have inserted the manufacturer name in the alloy designation.

Material properties

Duralumin is one of the aluminum alloys of the group AlCuMg (material number 2000-2999 ) and is used primarily cold cured. It is not very corrosion resistant, limited anodising and weldable. Today, the name duralumin is used primarily to lexical definition. Similar alloys are, however, still used in aviation.

Compared with pure aluminum duralumin has a slightly greater density. However, the tensile strength is 180 to 450 N / mm ² (according to other sources of up to 800 N / mm ² ), and thus up to the tenfold of pure aluminum, which has only about 80 N / mm ². Also the very important technical yield strength is 250 N / mm ² to 30 N / mm ² with pure aluminum. The situation is similar in the Brinell hardness, HB where a value of about 125 compared to 22 in pure aluminum is achieved. The elongation at break is indicated by 22 percent than three times higher value compared to 7 percent pure aluminum. Another important point was that duralumin by aging forfeited nothing of its strength.

The basis for the cure against pure aluminum is that after rapid cooling of the alloy after some time initially suppressed in deterring precipitation of a second phase (the intermetallic compound CuAl2 ) takes place in the basic structure of the alloy, a process which results in a significant increase in strength result. This separation of strength-increasing second phase may at both room temperature and at elevated temperatures take place ( " natural aging " - " artificial aging " ) and reaches its optimum after two days.

The hardening of aluminum alloys otherwise has nothing to do with the taking place in the steel quenching processes. There, the strength decreases after a reheating of the quenched steel in the Al alloys it increases.

The hardening of duralumin thus almost achieves strength softer steels. The comparison with pure aluminum higher susceptibility to corrosion is encountered by a coating of pure aluminum, anodizing or painting.

Applications

The improved material properties of the replacement of steel with an aluminum alloy in the aerospace and weapons technology was in the first sense. Previous alloys such as zinc -aluminum alloys were significantly more susceptible to corrosion and did not reach the required strength by far.

In 1911 took a Duralumin large-scale application for the supporting framework of the British airship HMA No. 1 Mayfly. From 1914 it was also used for the construction of the German Zeppelin airships ( LZ for the first time at 26 / Z XII ) are used. 1929 was an all-metal airship - the American ZMC -2 - made ​​. It was completely including a sheet - gas shell of duralumin.

In addition to the air shipbuilders Hugo Junkers was excited to use duralumin for the Junkers J7 (1917 ). One of the first passenger aircraft, the Junkers F 13 (1919), was a full -metal aircraft was used in the Duralumin as the material for the chassis. Duralumin was also well suited to the then-new monocoque construction of airframes. In modern aircraft duralumin is known today as the material in 2017, 2117 or 2024.

The use in motor vehicle was initially limited by the high price and the more difficult processing possible. However, it is now common, when it comes to a low weight. Examples for use are particularly body parts. Hoods and trunk lids are now largely replaced by thin-walled precision pressure casting ( EVACAL and PORAL method).

, Cited literature

• Paul krais Materials Volume 2, A. Barth, Leipzig, 1921, pp. 517 f
• Rompp, Chemie-Lexikon, 9th edition, publisher Regitz M. and J. Falbe, " Duralumin ( ium ) "
• A. von Zeerleder, technology of light metals, Rascher Verlag Zurich 1947
• Foundry Dictionary 17th Edition at Schiele and beautiful, Berlin 1997, editor Stephan Hasse, see duralumin