Abstract
In this paper, the microstructures and corrosion behaviors of as-cast Mg–5Sn–xGa alloys with varying Ga content (x = 0, 0.5, 1, 2, 3 wt %) were investigated. The results indicated that Ga could not only adequately refine the grain structure of the alloys, but could also improve the corrosion resistance. The microstructures of all alloys exhibited typical dendritic morphology. No Ga-rich secondary phases were detected when 0.5 wt % Ga was added, while only the morphology of Mg2Sn phase was changed. However, when the addition rate of Ga exceeded 0.5 wt %, an Mg5Ga2 intermetallic compound started to form from the interdendritic region. The volume fraction of Mg5Ga2 monotonically increased with the increasing Ga addition level. Although Mg5Ga2 phase was cathode phase, its pitting sensitivity was weaker than Mg2Sn. In addition, the standard potential of Ga (−0.55 V) was lower than that of Sn (−0.14 V), which relieved the driving force of the secondary phases for the micro-galvanic corrosion. An optimized composition of 3 wt % Ga was concluded based on the immersion tests and polarization measurements, which recorded the best corrosion resistance.
Highlights
Magnesium alloys, with their excellent properties of low density and high specific strength, have received extensive attention in automobile, aerospace, electronics, and other industries [1,2,3,4]
The purpose of this study is to explore the effect of Ga on the microstructure and corrosion resistance of Mg–5Sn alloy
The result suggests that the grain size decreased monotonically with increasing Ga content, probably due to the increasing grain growth restriction factor (GRF), which can be expressed by Equation (4) for a binary alloy [26]: GRF = mL C0 (k0 − 1)
Summary
With their excellent properties of low density and high specific strength, have received extensive attention in automobile, aerospace, electronics, and other industries [1,2,3,4]. Among many of the binary alloy systems, the Mg–Sn phase diagram demonstrates that the Mg-rich side has a very shallow α-Mg solvus curve, indicating that it is conducive to maximizing the precipitation of the thermally stable Mg2 Sn particles This infers that adding Sn potentially helps to enhance the mechanical integrity of the alloy at elevated temperatures [5,6,7,8,9]. Ha et al [13] observed that the main reason for the decrease of H2 evolution rate was that Sn elements were enriched on the metal surface. They further reported that Sn had a higher potential H2 evolution than the Mg matrix [15,16]. That is to say, when the matrix is corroded, the element Sn is spontaneously enriched on the matrix surface, acting as a barrier to further corrosion [13]
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