Sr is known to transform the morphology of the eutectic silicon phase as well as the Fe-rich β phase in Al-Si alloys, improving their mechanical properties. However, little is known about the effect Sr has on the (local) corrosion properties of aluminium alloys. This study investigates the effect of Sr addition to a modified AA3003 heat exchanger material on the morphology of the different phases present, especially the Fe-rich phases, as well as on the (local) corrosion properties of this material. This work reports the formation of a Sr-rich phase, which slightly increases the macrohardness of the material. The Fe-rich phases are not shown to be refined/influenced by the addition of Sr Potentiodynamic polarization experiments showed an increase in pitting potential by increasing the amount of Sr in the material up to 0.4 wt.%. Nevertheless, the analysis of the corrosion morphology revealed that the Sr-containing particles did not contribute to the corrosion process despite their cathodic behaviour compared to the Al matrix as measured by Scanning Kelvin Probe Force Microscopy. This behaviour was attributed to the thicker oxide layer found on the Srrich particles.
The AA3003 alloy is widely used as fin material in heat exchangers. The life time of these heat exchangers is mostly determined by their corrosion properties. Twin roll casting (TRC) of AA3003 material is known to often result in the formation of a macrosegregation area of alloying elements towards the centre plane of the casted strip (centre line segregation = CLS). Considering the potential exposure of cross-sectional areas of TRC material in the heat exchanger fin application, and the relatively high corrosion susceptibility of the CLS, the study of this region is of key importance to understand the microstructural effects on the resulting corrosion mechanisms and kinetics for these materials. Typically the alloys are homogenized to bring the microstructures closer to an equilibrium state, but the impact of this heat treatment on the corrosion properties is insufficiently studied. Therefore, this study investigates the effect of different homogenization procedures on the corrosion properties of the CLS and the interaction of the intermetallic particles with the surrounding aluminium matrix. This work shows that the pitting corrosion resistance is greatly dependent on the homogenization temperature, with better corrosion resistance obtained with higher temperature, especially near the CLS. This difference in corrosion behaviour is completely attributed to a difference in microstructure and not to an oxide layer effect. Furthermore, it is observed that not only temperature will have a large influence on the corrosion resistance, but duration of the heat treatment as well.
Aluminum alloys produced with Twin Roll Casting (TRC) technology still necessitate to be thoroughly investigated in some areas. Corrosion mechanisms operating under special conditions with the contribution of unique features of the microstructure are among those. Materials produced with TRC have unique features inherently generated due to the solidification path of the material during casting. Contrary to the very fine particles at the locations close to the free surface, centerline segregation (CLS) occurring at the mid-plane of the thickness have different morphological and compositional features than rest of the microstructure. While, unless directly exposed, it has almost no contribution to the general corrosion behavior of the alloy, some manufacturing processes generation new free surfaces in the material for CLS to be exposed to the corrosive media can be harmful for overall general corrosion performance of the alloy. It differentiates itself in corrosion behaviour with its compositional and morphological features than rest of the microstructure. Hence, influence of CLS on corrosion behaviour of two different alloys in 3000 and 8000 series employed for heat exchangers and packaging applications, respectively, are studied in the present study. Since CLS does not disappear with rolling passes but only changes its morphology, samples were taken at appropriate thickness of the downstream process that allow corrosion tests to be conducted at the cross section of the samples. Metallographical preparation techniques were used to reveal the CLS. Samples were dipped in to the HCl-NaCl containing test solution to observe the progress of corrosion in the matrix and heavily populated CLS areas during the course of test. Open-circuit potential (OCP) measurements were carried out on the rolled free surface, quarter plane and mid plane of the samples after milling the surface of the samples. Different samples produced with compositional and thermomechanical processing route variants were used. Results show that composition of the alloy and applied thermomechanical processes influence the corrosion characteristics of CLS and accordingly the overall corrosion performance. Other important finding is the contribution of manufacturing method to corrosion mechanism whether if it reveals the CLS by creating new free cross sectional surfaces.
Aluminium alloy (AA) 3003 is widely used as fin and tube material in heat exchangers. In these heat exchangers the tube and fin material are brazed together by means of an AA4xxx alloy. In this work, the effect of a simulated brazing step on the microstructure and corrosion behaviour of a twin roll casted (TRC) AA3003 was studied. In particular, the effect of simulated brazing on the corrosion properties of the centre line segregation (CLS) of alloying elements and the interaction of the intermetallic particles with the surrounding matrix is explored. It is shown that the cross sections are significantly more active than the surface of the TRC AA3003, revealing the importance of the CLS on the corrosion behaviour. Furthermore, it is shown that the number of pits and their depths decreased considerably on the exposed cross sections after simulated brazing, especially near the CLS. Scanning Kelvin probe force microscopy (SKPFM) measurements show that after the simulated brazing step the Volta potential difference between the intermetallic particles and the matrix reduced significantly. This change in the Volta potential could be caused by the slight increase of Si content in the matrix.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.