Front fixation plate - Al Cu Sn Zn Si Alloy - Modern Times

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

Stratigraphic representation: none

Fig. 4: Stratigraphic representation of the object in cross-section using the MiCorr application. This representation can be compared to Fig. 8.

Analyses performed:
Metallography (unetched), Vickers hardness testing, SEM/EDX.

The metal is an aluminium alloy containing Cu, Sn, Zn and Si (Table 1). The unetched metal shows an as-cast structure consisting of the aluminium matrix with Sn (not soluble in Al) inclusions (Figs. 4 and 5), intermetallic compounds such as Al2Cu (Fig. 4, red arrows) and clusters of Al,Fe,Cu & Si phases (Fig. 4, black arrows). There are porosities in the metal (Figs. 3 and 4). The average hardness of the metal is HV1 80.

 

Elements

Al Cu Sn Zn Si Fe O Fe Total
Metal (average) 89 4.6 3 1.6 1 < 0.8 < 100
Intermetallic compounds 45 55 < < < < < < 100
Al,Fe,Si,Cu phase clusters 58 11 < < 7.5 29 3.4 29 109
Sn inclusions < < 100 < < < < < 100

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

No corrosion layer can be seen on the metal surface (Figs. 3 and 6). Under polarized light small white and brown particles are visible on the broken edge (Fig. 7). Their analysis reveals the presence of silica particles surrounded by dirt (Table 2 and Fig. 8). The metal surface is covered by a thin oxygen bearing skin (Fig. 8).

 

Elements

O Al Si Cu Total
Adherent particle (average of 3 similar analyses) 55 0.6 50 1.1 106

Table 2: Chemical composition (mass %) of the adhering particles to the metal surface (from Fig. 7). Method of analysis: SEM/EDX, Laboratory of Analytical Chemistry, Empa.

Corrected stratigraphic representation: none

Although not common at the beginning of the 20th, this Al-Cu-Sn-Zn-Si cast alloy was extensively used on the Dufaux IV plane. No corrosion layer has been found on the metal surface except adherent silica-rich particles and the thin oxidised skin typical of Al alloys. The presence of these materials might be explained by the regular maintenance of the metal using abrasive silicon carbide paper.

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.

References on analytic methods and interpretation