Aircraft rear fastening plate VHS-497 - Al Alloy - Modern Times

Aircraft rear fastening plate VHS-497 - Al Alloy - Modern Times

Aircraft rear fastening plate VHS-497

Marianne. Senn (Empa, Dübendorf, Zurich, Switzerland) & Christian. Degrigny (HE-Arc CR, Neuchâtel, Neuchâtel, Switzerland)

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Credit HE-Arc CR.

Fig. 1: Fastening plate from the back of the Dufaux IV (left) and top view of the aeroplane showing its location (red dot, right) (www.hepta.aero),

Metal fastening plate for the wooden construction of the rear of the aeroplane (Fig. 1) covered with a thin corrosion layer.

Aeroplane part

Dufaux IV aeroplane

Biplane built by Henri and Armand Dufaux in 1909/10

Modern Times

Outdoor to indoor atmosphere

Swiss Museum of Transport, Luzern, Lucerne

Swiss Museum of Transport, Luzern, Lucerne

VHS-497

N/A

Complementary information

None.

Credit HE-Arc CR.

Fig. 3: Micrograph of the cross-section of the sample taken from the back fastening plate showing the location of Figs. 4 to 10,

Sample cut from the corner of the fastening plate (Fig. 2). Dimensions: L = 4mm ; W = 1.2mm.

Al Alloy

Hot rolled and annealed

DUF-12

HE-Arc CR, Neuchâtel, Neuchâtel

Swiss Museum of Transport, Luzern, Lucerne

September 2007, metallography and alloy composition

Complementary information

None.

Analyses performed:
Metallography (nital etched), Vickers hardness testing, SEM/EDS.

None.

The metal is a relatively pure aluminium alloy with numerous inclusions (Table 1). From the chemical composition of the inclusions they can be interpreted as alpha-AlFeSi intermetallic compounds. In bright field we observe elongated inclusions indicating that the metal was rolled (Fig. 4). The alloy composition is similar to an unalloyed primary aluminium (Al content between 99 and 99.8 mass%). The O content reflects the immediate oxidation of the metal and is not part of the alloy. After etching the organisation of inclusions in rows is more easily seen (Fig. 5). The SEM image shows large grains formed after annealing (Fig. 6). The average hardness of the metal is HV1 40.

 

Elements Al Si Fe O Total
Metal (average) 95 1 <1 1 97
Inclusion (average) 60 8 31 1 100


Table 1: Chemical composition (mass %) of the metal and inclusions (from Fig. 4). Method of analysis: SEM/EDS, Laboratory of Analytical Chemistry, Empa.

Credit HE-Arc CR.

Fig. 4: Micrograph of the metal sample from Fig. 3 (detail), unetched, bright field. The metal matrix is in white, the elongated inclusions in grey,

Credit HE-Arc CR.

Fig. 5: Micrograph of the metal sample from Fig. 3 (detail), etched, bright field. The metal matrix is in white, the elongated inclusions in dark-grey and black,

Credit HE-Arc CR.

Fig. 6: SEM image of the metal sample from Fig. 3 (detail), SE-mode, etched. We observe the presence of large grains and numerous elongated inclusions,

Recrystallized structure with large grains

Al

Si

Complementary information

None.

The metal is covered by a very thin corrosion layer (CP1). In addition to this, locally thicker adhering materials can be observed (NMM1, appearing as dark-grey area in Fig. 7). Under polarized light, they appear blue-brown (Fig. 8). Analysis by SEM-EDS indicates that the metal is, as expected, covered by a very thin Al and O-rich layer whereas the particles in the adherent material contain C, O, Si, Ca, Fe, Zn, S and even Ti (Figs. 9 and 10). The location of the adherent material and the presence of both Zn and Ti suggest that it is a residue of a paint coating.

Credit HE-Arc CR.

Fig. 7: Micrograph showing the metal - adhering material interface from Fig. 3 (reversed picture, detail), unetched, bright field. We observe in white the metal matrix and dark-grey the adhering material,

Credit HE-Arc CR.

Fig. 8: Micrograph (same as Fig. 7) and corresponding to the stratigraphy of Fig. 11, unetched, polarised light. We observe in grey the metal matrix and blue-brown the adhering material,

Credit HE-Arc CR.

Fig. 9: SEM image (same as Fig. 7, inverted picture, detail), BSE-mode, unetched,

Credit HE-Arc CR.

Fig. 10: Elemental chemical distribution of the selected area from Fig. 9. Method of examination: SEM/EDS, Laboratory of Analytical Chemistry, Empa,

Passive

Unknown

Complementary information

None.

Fig. 11: Stratigraphic representation of the sample taken from the back fastening plate in cross-section (dark field) using the MiCorr application. The characteristics of the strata are only accessible by clicking on the drawing that redirects you to the search tool by stratigraphy representation. This representation can be compared to Fig. 8, Credit HE-Arc CR.

None.

This aluminium alloy has a composition similar to a primary aluminium with an Al content between 99 and 99.8 mass%. The main impurities are Si and Fe. Because of their insolubility in the aluminium they form intermetallic (alpha-AlFeSi) inclusions. The metal was hot rolled and annealed. It is covered by a very thin corrosion layer (probably aluminium oxide) and in some areas adherent materials are present, most likely the remains of a Zn- and Ti-rich paint system mixed with environmental pollutants.

References on object and sample

References object
1. Rumo, L. (2008) Analyse et caractérisation des alliages constitutifs de l'avion Dufaux IV. Mémoire Filière conservation-restauration, Haute Ecole art appliqués, La Chaux-de-Fonds, 101-105.

References sample
2. Rumo, L. (2008) Analyse et caractérisation des alliages constitutifs de l'avion Dufaux IV. Mémoire Filière conservation-restauration, Haute école art appliqués, La Chaux-de-Fonds, 101-105.