Abstract
The objective of the present research is to study the corrosion susceptibility of two Al-Mg diluted alloys (Al-0.5wt.%Mg and Al-2wt.%Mg) with different grains structures obtained by directional solidification (columnar, equiaxed and columnar-to-equiaxed transition, CET) in 0.5% NaCl solution, at room temperature. The corrosion resistance is analyzed by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques in both longitudinal and transversal sections of the samples. The columnar grain zone presents higher corrosion resistance than the equiaxed grain zone. In addition, the transversal section shows higher corrosion resistance than the longitudinal section of the samples. Then, the Al-0.5wt.% Mg alloy displays higher corrosion resistance than the Al-2wt.% Mg alloy. The values of the polarization resistance are used as a basic criterion for the evaluation of the corrosion resistance of both alloys. In this way, when the polarization resistance decreases with the increasing in the distance from the base, the grain size, secondary dendritic arm spacings and hardness increases. In addition, when the polarization resistance increases, the critical temperature gradient decreases.
Highlights
IntroductionAluminum and its alloys stand out for two main properties: low density and excellent mechanical strength
We examined the susceptibility to corrosion of directionally solidified aluminum-magnesium diluted alloys (Al-0.5wt.%Mg and Al-2wt.%Mg) with different grain structures (columnar (C), equiaxed (E) and columnar-to-equiaxed transition, CET), obtained by a directional solidification process, in 0.5 M NaCl solution, at room temperature, using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) as principal electrochemical techniques
It is evident that the values of the resistance associated to the pores, R1 are higher for the longitudinal section than for the transversal section
Summary
Aluminum and its alloys stand out for two main properties: low density and excellent mechanical strength. These characteristics have led to its use in applications where weight is a determining factor, as it is the case in the transportation, automotive and naval industries (Davis, 1993; Canales et al, 2012; Jayalakshmi et al, 2013). The mechanical properties of pure aluminum did not meet the demands required in structural applications, and for that reason, its industrialization did not take place until 1930 with the design of aluminum-based alloys. The incorporation of alloying elements enables a considerable increase in mechanical properties, which in turn, widens its range of applicability (Shu-qing and Xing-fu, 2014; Kaygisiz and Marasli, 2015)
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