Abstract
Since several years the importance of aluminium in the automotive industry is growing, due to its lower density compared to steel. Before an aluminium sheet can be used in a car it needs to undergo several treatments and requires several successive coatings. The initial layer on the bare metal is conventionally a conversion coating. The purpose of this coating is two folded. First, it is applied to enhance of the adhesion properties of the aluminium surface towards the successive layers (e.g. zinc phosphate). Secondly, the conversion coating forms a first corrosion protection layer on top of the second phase particles at the surface. In the past these conversion coatings were chromium based but are now banned. Although new alternatives, like the Zr-Ti based coatings, are already commercially used, a lot of their behaviour and properties are still to be discovered.
Several techniques can be used to apply the conversion coating, divided in rinse (dipping) and no-rinse (spraying and roller coater) applications. Though published research was only focused on dip applications. In this literature it was already pointed out how the surface metallurgy, especially the second phase metallic particles, of the aluminium influence the formation and growth of the conversion coating.1-3
To analyse this 10-20 nm thick conversion coating the FE-AES system is an excellent tool. The nanometre depth and lateral resolution of the system makes it possible to investigate the coating distribution near the intermetallic particles on a sub-micrometre scale. Line scans, point analysis and depth profiling, were used to reveal interesting coating concentration changings near the intermetallic particles. By data analysis of the semi-quantitative measurements, statistical conclusions could be obtained.
Also FE-SEM-EDS was used to investigate the conversion coating near the intermetallic particles. In this case point analysis, line scans and mappings were obtained. Although SEM-EDX is not the most recommended technique to analyse this nanometre thin coating, interesting results were obtained. This provides the possibility to do a comparison between the analysis possibilities of FE-AES and FE-SEM-EDS when investigating the conversion coating distribution near second phase surface particles.
All measurements were performed on mill-finished automotive aluminium alloys, coated with a Zr-Ti based conversion coating applied by an industrial spraying process.
1. Lunder, O. et al. Surf. Coatings Technol. 184, 278–290 (2004).
2. Andreatta, F. et al. Surf. Coatings Technol. 201, 7668–7685 (2007).
3. Cerezo, J. et al. Appl. Surf. Sci. 366, 339–347 (2016).
Several techniques can be used to apply the conversion coating, divided in rinse (dipping) and no-rinse (spraying and roller coater) applications. Though published research was only focused on dip applications. In this literature it was already pointed out how the surface metallurgy, especially the second phase metallic particles, of the aluminium influence the formation and growth of the conversion coating.1-3
To analyse this 10-20 nm thick conversion coating the FE-AES system is an excellent tool. The nanometre depth and lateral resolution of the system makes it possible to investigate the coating distribution near the intermetallic particles on a sub-micrometre scale. Line scans, point analysis and depth profiling, were used to reveal interesting coating concentration changings near the intermetallic particles. By data analysis of the semi-quantitative measurements, statistical conclusions could be obtained.
Also FE-SEM-EDS was used to investigate the conversion coating near the intermetallic particles. In this case point analysis, line scans and mappings were obtained. Although SEM-EDX is not the most recommended technique to analyse this nanometre thin coating, interesting results were obtained. This provides the possibility to do a comparison between the analysis possibilities of FE-AES and FE-SEM-EDS when investigating the conversion coating distribution near second phase surface particles.
All measurements were performed on mill-finished automotive aluminium alloys, coated with a Zr-Ti based conversion coating applied by an industrial spraying process.
1. Lunder, O. et al. Surf. Coatings Technol. 184, 278–290 (2004).
2. Andreatta, F. et al. Surf. Coatings Technol. 201, 7668–7685 (2007).
3. Cerezo, J. et al. Appl. Surf. Sci. 366, 339–347 (2016).
| Original language | English |
|---|---|
| Publication status | Published - 28 Sep 2017 |
| Event | European conference on applications of surface and interface analysis 2017 - Montpellier, France Duration: 24 Sep 2017 → 29 Sep 2017 |
Conference
| Conference | European conference on applications of surface and interface analysis 2017 |
|---|---|
| Country/Territory | France |
| Period | 24/09/17 → 29/09/17 |