Towel bar - Al Alloy - Modern Times - France

Christian. Degrigny (HE-Arc CR, Neuchâtel, Neuchâtel, Switzerland)

Complementary information

Nothing to report.

Stratigraphic representation: none.

Fig. 4: Stratigraphic representation of the object in cross-section 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. 9, credit MiCorr_HE-Arc CR, C.Degrigny.

Complementary information

Nothing to report.

Analyses performed: 
Metallography, SEM/EDS.

The metal is a relatively pure aluminium alloy with numerous inclusions (Fig. 5). From their chemical composition they can be interpreted as Al3Fe intermetallic compounds (Fig. 6). Pitting corrosion as well as a start of intergranular corrosion develops locally under the deposits, outlining some of the grains (Fig. 5). 

Complementary information

Nothing to report.

A very thin and loose oxide film has formed on the metal surface (CP1) and is locally covered by white deposits (D1). Intergranular corrosion has developed under the deposits (Fig. 7). Analysis by SEM-EDS indicates that the Al and O-rich oxide layer is contamined with P and Si (area 1 on Fig. 7 and Fig. 8). These elements are even more present at the interface between CM1 and CP1 with Cl and S (area 2 on Fig. 7 and Fig. 9). The concentration of P and Si decreases in CM1 (area 3 on Fig. 7 and Fig. 10) while the concentration of S and Cl increases (Fig. 11). The deposit is mainly constituted of Ca, O, C and Si (probably CaCO3 and SiO2, area 4 on Fig. 7 and Fig. 12).

Complementary information

Nothing to report.

Corrected stratigraphic representation: none.

This aluminium alloy has a composition similar to a primary aluminium with an Al content between 99 and 99.8 mass%. The main impurity is Fe forming intermetallic (Al3Fe) inclusions. It is covered by a thin oxide layer (probably aluminium oxide). Pitting corrosion has formed under calcareous white deposits with a local distribution. It seems to develop as intergranular corrosion.

References object

1. Degrigny, C. (2018) Etude, identification des objets en aluminium patriminoniaux et classification de leurs forms de corrosion - projet EtICAL, rapport interne HE-Arc CR.

References sample

2. Degrigny, C. (2018) Etude, identification des objets en aluminium patriminoniaux et classification de leurs forms de corrosion - projet EtICAL, rapport interne HE-Arc CR.