Abstract
The AZ91D magnesium alloy was immersed in 3.5 wt.% NaCl solution at room temperature for times ranging from 1 minute up to 72 hours. The aim was to investigate the evolution of the corrosion process using confocal laser scanning microscopy (CLSM), electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy. The microstructure of the as-received alloy was initially characterized by optical microscopy and scanning electron microscopy (SEM). The crystalline phases were identified by X-ray diffractometry. The main phases were primary-α, eutectic-α, andβ(Mg17Al12). Vickers microhardness markings were made on the surface of one etched sample to facilitate the identification of the same region at each different immersion time, thus enabling the observation of the corrosion process evolution. Corrosion initiates at the grain boundaries of the eutectic microconstituent and, then, propagates through primaryα-grains. Theβ-phase was less severely attacked.
Highlights
Weight reduction is a serious concern in the automotive and aerospace industries
The data were acquired after the same immersion times evaluated during the immersion test (Section 2.3) in order to complement the characterization of the evolution of the AZ91D corrosion process
The results presented were allowed to fully characterize the as-cast microstructure of the AZ91D
Summary
Weight reduction is a serious concern in the automotive and aerospace industries. Magnesium alloys are the state-of-theart materials when high strength-to-weight ratio is pursued. Recyclability and good machinability are additional attributes that make them attractive materials to manufacture low weight parts [4] In spite of these attractive attributes, the well-known chemical instability in aqueous environments is a core issue for magnesium alloys, limiting their applicability [5,6,7]. Large volume fractions and continuous distribution across the matrix are considered to be beneficial to the general corrosion resistance of the alloy by forming a protective layer of aluminum-rich surface oxide. By contrast, if it is discontinuous and concentrated in small areas due to its relative low volume fraction, it can accelerate galvanic corrosion effects, acting as local cathodes [15,16,17,18]. Confocal laser scanning microscopy (CLSM) is a powerful tool for investigating the onset of corrosion processes at International Journal of Corrosion
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