Bugatti cooling system pipe - Al Alloy - Unknown - France

Bugatti cooling system pipe - Al Alloy - Unknown - France

Bugatti cooling system pipe

Christian. Degrigny (HE-Arc CR, Neuchâtel, Neuchâtel, Switzerland) & Elodie. Granget (HE-Arc CR, Neuchâtel, Neuchâtel, Switzerland) & Brice. Chalançon (MNAM (Musée National de l'Automobile de Mulhouse), Mulhouse, Alsace, France)

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Credit He-Arc CR, E.Granget.

Fig. 1: Bugatti water pipe, unknown model,

Credit He-Arc CR, E.Granget.

Fig. 2: Examples of water pipes located on a Type 37 engine,

This section of a pipe was given to the MNAM as study material, without indication of provenance. The pipe is angled, sharply cut on one end and heavily corroded on the other, the inside being clugged by a brittle yellowish deposit.

Looking at its shape, it is safe to assume that this is an exit pipe from the upper part of the engine (Fig. 2 and complementary information below).

Technical object

MNAM (Musée National de l'Automobile de Mulhouse), Mulhouse, Alsace, France

Unknown

Unknown

Outdoor to indoor atmosphere

MNAM (Musée National de l'Automobile de Mulhouse), Mulhouse, Alsace

MNAM (Musée National de l'Automobile de Mulhouse), Mulhouse, Alsace

None

N/A

Complementary information

A combustion engine transforms thermal energy into kinetic energy. This process is imperfect and releases a lot of heat through the block of the engine. Therefore, these parts need to be cooled down. A cooling system circulating water between the block [hot] and a heat exchanger (or radiator) [cold] is frequently used to fulfill this function (Poulain, 1995, p.86). Most of the time, the Bugatti inline cylinder engines have aluminium water pipes entering the block from below and exiting it from above, as shown on Fig.2.

This artefact is part of the "Materials for study Library" that the museum collected. It can therefore be sampled.

Credit He-Arc CR, E.Granget.

Fig. 3: Heavily corroded side of the Bugatti water pipe showing the sampling area indicated in red,

The schematic representation below gives an overview of the corrosion layers encountered on the Bugatti water pipe. 

The stratum M is an aluminium alloy. Three CP strata have been identified. CP3 has a greyish mate color and is covering all of the corroded side of the pipe. Scattered over this uniform layer, blue-green (CP2) and white (CP1) spots of corrosion products can be found.

Credit He-Arc CR, E.Granget.

Fig. 4: Stratigraphic representation of the corrosion structure of the external surface of the water pipe from visual macroscopic observation,

Fig. 5: Stratigraphic representation of the Bugatti water pipe observed macroscopicallly under binocular 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. 4, Credit HE-Arc CR, E.Granget.
Credit He-Arc CR, E.Granget.

Fig. 6: Micrograph of the sample taken from the corroded exit pipe of the Bugatti water pump (Fig. 3), showing the location of Figs. 7-8 and 11 to 14 in red,

A radial section of the pipe has been sampled and embedded as shown on Fig.6.  

The cross-section shows not only the metal sampled but the accompanying thick yellow deposit that was clugging the pipe. Pitting corrosion develops all along the profile of the sample. A selected area (in red) is further investigated in Figs. 7-8 and 11-14.

Al Alloy

Cast

None

HE-Arc CR, Neuchâtel, Neuchâtel

MNAM (Musée National de l'Automobile de Mulhouse), Mulhouse, Alsace

31.12.2019 - Sampled for Metallography

Complementary information

The yellow deposit that was clugging the pipe could not be properly analysed (see Analyses and results below). Indeed, the deposit was way softer than the metal and suspected to contain organic compounds coming from the engine's coolant.

Analyses performed on the pipe: 
XRF with portable X-ray fluorescence spectrometer (Niton XL3t 950 Air Goldd+ analyser Thermo Fischer (voltage 50V, General metals mode with acquisition times 20s (Main) /20s (Low) /20s (Light).

Sample preparation: 
Due to a significant difference between the metal and the deposit hardness, and in order to preserve the corrosion layers, the surface preparation was realized with an alcoholic lubricant instead of water. Thus, the quality for the metal and corrosion layers have been priviledged over the deposit, as the alcohol might have corrupted the suspected organic compounds of the deposit. (See Sample: Complementary information above).

Analyses performed on the cross-section sampled from the pipe: 
Metallography (unetched), BF and DF imaging; SEM-EDS (20kV), SE and BSE imaging and semi-quantitative EDX analysis.

Although XRF was used, no results are included in this sheet.

The metal is an aluminium alloy containing both Cu and Zn. It is slighly porous (Fig. 7, red circles). Its dendritic microstructure is revealed by observation in bright field (Fig. 8) and with SEM (Fig. 9).

Element mass %
Al 89
Cu 7
Zn 2.5
Fe 1
Si 0.5

Table 1: Chemical composition (mass %) of the metal the water pump pipe. Method of analysis: SEM/EDS, HE-Arc Ingénierie, S.Ramseyer.

Zn is uniformely present in the alloy. There are two interdendritic phases (Fig. 12): a eutectic phase containing Al, Fe and Cu, and a second phase containing mostly Al, Cu. Additionally Sn and Si precipitates could be identified.

Credit HEI Arc, S.Ramseyer / Edit: He-Arc CR, E.Granget.

Fig. 7: Micrograph of the selected area shown on Fig.6 (rotated by 90°), unetched, dark field with indication of pores (red circles),

Credit HEI Arc, S.Ramseyer / Edit: He-Arc CR, E.Granget.

Fig. 8: Micrograph similar to Fig. 7, unetched, bright field showing the locations of Fig. 9 (in red) and Fig. 10 (in blue),

Credit HEI Arc, S.Ramseyer.

Fig. 9: SEM image (BSE mode) of the metal sample from Fig. 8 showing the microstructure of the pipe. Dark grey = main phase (Al), medium grey = interdendritic phase 1 (eutectic Al, Fe, Cu), light grey = interdendritic phase 2 (Al, Cu) and white = precipitates (Si, Sn),

Credit HEI Arc, S.Ramseyer.

Fig. 10: Close-up image of Fig. 9,

Credit HEI Arc, S.Ramseyer / Edit: He-Arc CR, E.Granget.

Fig. 11: SEM image and EDS elemental chemical distribution of main and interdendritic phases of the pipe. 20kV,

Credit HEI Arc, S.Ramseyer.

Fig. 12: Fe (red), Cu (green) and Sn (blue) chemical distribution of the area of Fig. 8. Method of analysis: SEM-EDS. Lab. of Electronic Microscopy and Microanalysis, Néode, HEI Arc,

Dendritic structure

Al

Si, Fe, Cu, Zn

Complementary information

None.

The BF and DF images (Figs. 7 and 8) show a few big cracks at the interface between CM1 and M1. The SEM image shows that they expand in a network of additional microcracks (Fig. 13). The pipe suffers from a uniform interdendritic corrosion. The Al, Cu and Zn phase is oxidising preferentially, developing then aluminium oxides, versus the interdendritic phases. In some places, pits of corrosion formed. SEM cartography showed a concentration of Cl at the base of the pit (Fig. 14: Green).

Credit HEI Arc, S.Ramseyer.

Fig. 13: SEM image of the pitting corrosion of the pipe. BSE, 20kV. Black = Cracks, Dark grey = oxydation, Medium grey = main phase, Light grey = interdendritic phase,

Credit HEI Arc, S.Ramseyer.

Fig. 14: SEM cartography of a pit of corrosion developing on the pipe. 20kV. Red = Al, Green = Cl, Blue = O,

Multiform - pitting

Unknown

Complementary information

None.

Fig. 14: Stratigraphic representation of the sample taken from the Bugatti water pipe 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. 7 and 8, Credit HE-Arc CR, E.Granget.

The schematic representation of corrosion layers of Fig. 4 integrating additional information based on the analyses carried out is given in Fig. 15. 

Credit He-Arc CR, E.Granget.

Fig. 15: Improved stratigraphic representation of the exit pipe,

This angled water pipe, coming from a Bugatti engine's cooling system, is made of cast Al, Cu, Zn, Fe alloy and shows a slightly porous dendritic microstructure. There are two interdendritic phases, a eutectic Al, Fe, Cu phase and a Al, Cu phase, as well as precipitates of Si and Sn.

One end of the pipe is heavily corroded and entirely clugged by corrosion products and other deposits on the inside. This deposit could not be analyzed.

The external surface shows a uniform interdendritic corrosion preferentially consuming the dentritic phase (Al, Cu, Zn). Pitting corrosion has been identified, with Cl pockets at the base of the pit.

References on object and sample

References object
1. Poulain, P. and J-M. (1995) Voitures de collection : Restauration Mécanique Editions Techniques pour l’Automobile et l’Industrie (ETAI), Paris.
2. Granget, E. (2020).La corrosion des alliages d’aluminium des circuits de refroidissement à eau de véhicules en contexte patrimonial : Utilisation d’outils open-access dans l’établissement d’un diagnostic des altérations d’un corpus de véhicules conservés au Musée National de l’Automobile de Mulhouse (Collection Schlumpf), Rapport interne MNAM.

References sample
3. Granget, E. (2020).La corrosion des alliages d’aluminium des circuits de refroidissement à eau de véhicules en contexte patrimonial : Utilisation d’outils open-access dans l’établissement d’un diagnostic des altérations d’un corpus de véhicules conservés au Musée National de l’Automobile de Mulhouse (Collection Schlumpf), Rapport interne MNAM.

References on analytic methods and interpretation

4. Vargel, C. (2004) Corrosion of Aluminium, Elsevier.
5. Degrigny, C. (2018) Etude, identification des objets en aluminium patrimoniaux et classification de leurs formes de corrosion - projet ETICAL, rapport interne HE-Arc CR.