Abstract
Paper presents the results on the corrosion behavior of some Al-Fe-Si, Al-Mg-Si and Al-Mg-Mn alloys in their final commercially usable tempered state. Durability of alloys was quantified and compared in the sense of corrosion rates in aqueous solutions while also having in mind the role of alloy chemistry. Open circuit corrosion potential (OCP) measurements, linear polarization and potentiodynamic anodic/cathodic polarization was employed in order to determine the corrosion behavior of samples in the mixture of chloride ions containing aqueous corrosion ambient. We found out that AlFe0.83Si0.18(AA8079), AlMg0.63Si0.72 (AA6005) and AlMg4Mn (AA5182) alloy exhibited the highest rates of passivation in 0.51 mol NaCl solution. The group of Al-Fe-Si alloys exhibited the greatest sensitivity to the changes in chemical composition under potentiodynamic polarization. Artificially aged Al-Mg-Si extruded profiles and fully annealed (after cold rolling) Al-Mg-Mn sheets exhibit very similar levels of equilibrium potentials E(I=0) in 0.51 mol NaCl solution. In the case of Al-Fe-Si alloys, we found that Fe/Si ratio also plays an important role, next to the total content of Fe and Si. Alloys with high Fe/Si ratios showed almost 30 % lower polarization resistance compared to the alloys with balanced Fe/Si, even in the case of the equal total content of alloying elements. The AlMg0.7Si1.2Mn0.8 alloy aged after quenching in the sprayed water and AlMg4Zn1.3Mn0.4 annealed sheet exhibit very similar levels of corrosion rates in 0.51 mol NaCl solution.
Highlights
From a corrosion perspective, aluminum and its alloys have been a successful metal materials used for many applications like commodity roles, automotive and vital structural components in aircrafts
The samples of Al-Fe-Si and Al-Mg-Mn alloys were tested as recrystallized sheets after cold rolling, and Al-Mg-Si alloys were tested as heat treated, i.e. artificially aged after quenching
It can be observed that the onsets of the open circuit corrosion potentials (OCP) for all alloys are shifted in the direction of more electropositive values, and the shapes of the curves that represent the evolution of Ecorr for different series of tested aluminum alloys are similar
Summary
Aluminum and its alloys have been a successful metal materials used for many applications like commodity roles, automotive and vital structural components in aircrafts. Pure aluminum has good corrosion properties due to formation of the strongly bonded barrier oxide film. This protective oxide layer is especially stable in near-neutral solutions of most non-halide salts leading to excellent pitting resistance. Alloying elements are added to aluminum for various reasons with improving mechanical properties as the principal reason These elements introduce heterogeneity into the microstructure, which is the main cause of localized corrosion that initiates in the form of pitting, and each alloying element has a different effect on the corrosion of aluminum [2]. These microstructural heterogeneities frequently have corrosion potentials differing from that of the solid solution matrix resulting in local (micro-) galvanic cells and it which can be experimentally quantified [1, 3,4,5,6,7]
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