COMPARISON OF CORROSION BEHAVIORS OF B1, BA11, BZ11 AND BC11 MAGNESIUM ALLOYS
Abstract
The Mg-Bi alloy, commonly referred to as the "green metal," finds extensive applications in industries such as automotive and aerospace due to its exceptional corrosion resistance. The corrosion performance of this alloy is intricately linked with its elemental composition. In this investigation, four distinct types of homogeneous magnesium alloys were meticulously prepared: Mg-1Bi (B1), Mg-1Bi-1Al (BA11), Mg-1Bi-1Al (BZ11), and Mg-1Bi-1Cu (BC11). Subsequently, a comprehensive analysis was conducted to examine the microstructures and corrosion behaviors exhibited by these magnesium alloys, exposed to a 3.5 w/% NaCl aqueous solution. The corrosion resistance test reveals that the corrosion resistance ranking of the four materials is as follows: BZ11 > BA11 > B1 > BC11. Among them, the uniform state of BZ11 alloy exhibits the lowest corrosion rate, measuring 0.548 mm·y–1, primarily attributed to its fine grain size and a small amount of dispersed second phase particles. Conversely, the uniform state of BC11 alloy demonstrates inferior corrosion resistance due to a high content of second phase particles within the alloy composition. SEM and EDS techniques were employed for microstructure characterization of all four magnesium alloys. The results indicate that localized corrosion occurs in all four alloys, with the electrochemical corrosion between the second phase particles and the matrix being specifically identified as the primary cause for degradation of BC11 alloy. XRD analysis confirms that in Mg-Bi alloy, the α-Mg phase coexists with block- or strip-shaped Mg3Bi2 phases as secondary phases. In contrast, BA11 and BZ11 alloys exhibit no change in secondary phases, consisting mainly of the α-Mg phase and Mg3Bi2 phase. On the other hand, BC11 alloy predominantly contains the α-Mg phase, Mg3Bi2 phase, and reticular Mg2Cu as secondary phases.
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