Abstract
Research and/or Engineering Questions/Objective
The context of this study is the microbial contamination of Aluminium heat exchangers. Different studies have been performed on microbial corrosion but only on steel and stainless steel alloys. These studies revealed an important impact of some bacteria on steel material corrosion resistance but the process takes a lot of time. We know that microbial contamination of parts lead to odour problem and now we have to demonstrate if the contamination can be harmful to Aluminium corrosion resistance and especially in a very short time.
Methodology
We performed our study on different parts taken from vehicles after different mileages and also on new parts. Microbial contamination extraction was performed initially on each exchanger (from Aluminium core and from product foams). Then the isolation of each microbial strain was performed to determine the orientation and the nature of each bacterium, yeast and mold present on the exchanger. Each microbial strain was identified by RNA sequencing. To study the impact of each microbial strain on Aluminium corrosion, the Aluminium samples were inoculated under optimum growth conditions. Different kinds of surface treatments were evaluated during this study. One of them is dedicated to protection against corrosion and the other to prevention against odours.
Results
Microbial contamination was evaluated on 3 parts (1 new part and 2 parts after mileage on vehicle). Concentration and number of bacteria, yeasts and molds increase with mileage. No anaerobic sulphite-reducing bacterium was found on parts. This kind of microbial contamination could be responsible for Sulfuric acid production which can lead to Aluminium corrosion. To study the impact of microbial contamination on Aluminium corrosion resistance, inoculation during a 4 week period of the bacteria, yeasts and molds identified on exchangers was performed on different Aluminium samples. The analysis of these samples will demonstrate if corrosion can be due to microbial contamination or if the microbial impact results only in odours.
Limitations of this study
Limitation of this study is the automotive field of application because the microbial contamination is very specific to the Aluminium exchangers present inside vehicle architecture.
What does the paper offer that is new in the field including in comparison to other work by the authors?
The investigation of the Aluminium corrosion due to microbial contamination was not identified before and our study has to demonstrate that this corrosion could happen very quickly and/or accelerate the corrosion process.
Conclusions
Microbial contamination of Aluminium heat exchangers, integrated inside vehicle architecture, increases with mileage and time very quickly. If the microbial contamination can lead to corrosion of Aluminium in specific conditions, this has to be evaluated and taken into account in component designs (surface treatment, specific tests...).
KEYWORDS – Aluminium, exchanger, microbial contamination, corrosion