Hispano-Suiza water pump - Al Cu Sn Zn Si Alloy - Modern Times

Granget. Elodie (, None) & . (MNAM (Musée National de l'Automobile de Mulhouse), Mulhouse, Alsace, France)

Complementary information

This engine part was given to the MNAM as reference material for a study on aluminium corrosion in engine cooling systems. Neither the model of the car nore the full context of use and conservation are known.

The schematic representation below gives an overview of the corrosion layers encountered on the object from a first visual macroscopic observation

Fig.1: Stratigraphic representation1 of the water pump in cross-section using the MiCorr
Fig.2: Stratigraphic representation 2 of the water pump in cross-section using the MiCorr

XRF-EDS analysis with Niton® XL3t [Thermo Fisher Scientific]: General Metals Mode

Voltage: 50V

Energy Max: 50KeV

Anode: Silver

MAIN RANGE (no filter)30 sec

LOW RANGE (filter Cu)15 sec

LIGHT RANGE (filter Ti)15 sec

 

The alloy has been identified by EDF-XRF as

Body  :Al88.3 Si10.1 Cu0.8 Fe0.6 Zn0.1 Pb0.1

Fixation  :Al90.6 Cu6.5 Sn 1.7 Fe0.7 Si0.5

Taking those results into account and looking at the corrosion differences, it appears that those two parts are made of very different alloys.

Historically, Al-Cu alloys appeared before Al-Si for the making or casted car parts. In practice, a machanic wouldn't necessary replace the whole pump if only the body seems to be problematic. It is therefore possible that the fixation is still the original piece and that the body is a more recent one.

Complementary information

This is an hypothetical structure based on the manufacturing technique used to create this engine part

This part of the pump is so heavily corroded, the exit pipe is now missing. 

One can recognize products of Copper (from the alloy) and Iron (probably from the steel screws nearby) imbeded in the Aluminium corrosion.

The white layers of corrosion are more powdery than the ones charged with Fe or Cu products. The metal has been completely consumed, following the dendritic microstructure of the alloy.

 

Complementary information

Pas très détaillé les "corrosion type" pour l'Aluminium. Je ne sais que mettre et ne peux pas insérer de nouvelles formes

This aluminium water pump displays a case of heavy transgranular corrosion caused by combined factors such as erosion caused by the water propulsed against its exit pipe, and galvanic corrosion. Indeed, the body of the pump seems to be a replacment part made out of a newer and more stable Aluminium silicium alloy. Moreover, the fixation is an aluminium cupper alloy with a significant amount of tin. Those two parts being directly in contact, galvanic corrosion helped to speed up the corrosion process. Tin could have be another alterating factor with regards to its problematic behavior toward temperature variations.

The fixation displays a case of heavy transgranular corrosion caused by combined factors such as erosion caused by the water propulsed against its exit pipe, galvanic contact with more stable metals, and potentially the presence of tin it the alloy. 

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