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Alfred Wilm et les débuts du Duralumin
Abstract
L'aluminium est un métal récent. L'étude de ses alliages est à situer dans un contexte militaro-industriel, particulièrement pour la découverte du plus important d'entre eux, le Duralumin qui doit son nom autant au fait qu'il est dur qu'au fait qu'il a d'abord été produit industriellement à Düren. L'ingénieur prussien Alfred Wilm avait été mandaté à Neubabelsberg près de Berlin pour obtenir un tel alliage et en ce sens cette découverte n'a pas le caractère romantique qu'on lui a parfois prêté. Je souligne également les relations de coopération et de concurrence internationale âpre qui ont accompagné les premières recherches sur cet alliage au début du XXe siècle. (with nine pictures)
Supplementary resource (1)
... Depuis la découverte d'Alfred Wilm en 1906(Hardouin Duparc 2005, certaines séries d'alliages d'aluminium, appelées alliages à durcissement structural, sont connues pour pouvoir être durcies par traitement thermique. C'est le cas des séries 2000, 6000 et 7000. ...
Ces travaux de thèse réalisés entre l’IRT Saint Exupéry et le CEMES, Université de Toulouse, CNRS ont pour objet l’étude d’alliages de la série 2000 pour des utilisations à des températures intermédiaires, de l’ordre de 200°C. La possibilité d’utiliser ces matériaux à cette température permettrait aux industriels du secteur aéronautique de réduire les coûts de production d’une part, et de diminuer les coûts d’exploitation des aéronefs ainsi plus légers d’autre part.Afin de répondre à cette problématique industrielle, deux nuances commerciales ont été considérées : le 2219-T851 et le 2050-T84. Ces nuances, déjà utilisées dans l’industrie aéronautique, ont été caractérisées à différentes échelles d’observation tout au long d’un vieillissement isotherme à 200°C allant jusqu’à 10000 h. Des observations effectuées à l’aide de divers microscopes optiques et électroniques et couplées à des essais mécaniques macroscopiques ont permis de déterminer l’évolution de ces nuances vieillies dans de telles conditions.Les résultats de cette étude montrent une importante stabilité thermodynamique des précipités nanométriques θ'-Al2Cu. Ces précipités constituent la microstructure fine de la nuance 2219-T851 à réception et apparaissent au cours du vieillissement au sein de la nuance 2050-T84 au détriment des précipités T1-Al2CuLi pourtant à l’origine des meilleures performances mécaniques avant vieillissement. Les évolutions microstructurales sont mises en lien avec les propriétés mécaniques en traction. Ces résultats montrent un intérêt industriel pour la nuance 2219-T851 dont la stabilité des propriétés a été montrée dès 1000h de vieillissement.
Aluminum alloys are very interesting witnesses of industrial and technical development. The first ever developed was Duralumin, a light metal with good mechanical properties. In the 1930s, the rise of nationalism stimulated research and development, generating various aluminum alloys. This work reports the comparison of two versions of aluminum alloys, which were found in collected parts of WWII crashed aircraft from four nations: a Messerschmitt Bf 109 (DE), a Dewoitine D.520 (FR), and a P-51 Mustang (USA) and an Avro Lancaster (United Kingdom). The first version of alloy with magnesium content below or equal to 1 wt.% and the second version with higher magnesium content (1.5 wt.%), were identified as respectively AlCuMg1, AlCuMg2 in Germany; Duralumin, Duralumin F.R. in France; Hiduminium DU Brand, Hiduminium 72 in the UK and 17S, 24S in the USA. This study uses a multiscale approach based on historical research complimented by laboratory analyses of materials directly collected on the crashed aircraft. It allows a comparison and a better knowledge of the alloys used in each nations: their chemical composition, designations, microstructure, and mechanical properties are investigated.
Precipitation in Duralumin, a historic quaternary alloy of the type: Al–Cu–Mg–Si, was never fully studied nor observed by current electron microscopy techniques. This article presents the full characterization and comparison of two alloys: a Duralumin (A-U4G) from the 1950s collected on a vintage aircraft and its modern equivalent: a 2017A alloy. The as-received and peak-aging states were analysed with DSC, SAXS and TEM advanced techniques. It is shown that old Duralumin and modern 2017A present a similar nanoprecipitation in the as-received state and behave similarly upon artificial aging. As opposed to what has been reported in the past, three types of precipitates participating in hardening were found upon aging: θ’-Al2Cu, Q’(Q)-AlCuMgSi and Ω-Al2Cu.
In many countries, collections of historic aircraft, conserved in Air and Space museums or local associations, reflect the importance of a national or local history. Mostly parked outdoors, aircraft suffer from significant corrosion requiring conservation operations. During renovation, metallic parts are often replaced by association members. This can lead to a major loss of information since industrial archives dealing with materials and processes do not always survive. However, if these elements can be considered, they could be a fundamental source of information on the materials originally used and of the technical history of aeronautics. This work reports a thorough study of aluminium-based alloy parts collected on a Breguet aeroplane dating from the 1950s, during its recent renovation. Thanks to an approach coupling multi-scale material characterisation and research in archives, information on the industrial knowledge is revealed. Several historic grades of aluminium-based alloys were found, namely A-U4G, A-U4G1, and A-U3G, depending on the role of the part. Similarly, different protective coatings were identified (anodic oxidation, primers, and paintings), depending on the role of the metallic part and its location in the plane. Knowledge of the materials from bulk metal to the coated surface is necessary for good conservation practices regarding aeronautical heritage artefacts. Related documents and archives also fundamentally help in understanding such complex artefacts.
Study of Aluminium Alloys for the Development of Aircraft Preservation Treatments
This article looks at a unique aluminium alloy, Duralumin. Its appearance in the early 20th century made the development of aviation possible. It was the predominant material in aircraft. In the material’s early years its composition, heat treatments and shaping could vary depending on where it was produced. These variations led to changes in its metallographic structure and its sensitivity to corrosion. Not all aircraft kept as well. The preservation of these aircraft wrecks is a challenge that must combine scientific knowledge of the material with historical data. The study on the development of preservation treatments for the alloy illustrates that approach. It was conducted on two propeller blades dating from the Second World War. Their metallographic analysis confirmed they were shaped by forging and showed differences in the distribution of inclusions, probably corresponding to different production origins. Analyses also showed the very slight presence of chloride ions. Dechlorinating treatments therefore proved useful for these objects.
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