Microstructure, Tensile Properties, and Corrosion Behavior of Die-Cast Mg-7Al-1Ca- x Sn Alloys
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Microstructure, Tensile Properties, and Corrosion Behavior of Die-Cast Mg-7Al-1Ca-xSn Alloys Feng Wang, Haikuo Dong, Shijie Sun, Zhi Wang, Pingli Mao, and Zheng Liu (Submitted December 26, 2016; in revised form November 21, 2017; published online January 19, 2018) The microstructure, tensile properties, and corrosion behavior of die-cast Mg-7Al-1Ca-xSn (x = 0, 0.5, 1.0, and 2.0 wt.%) alloys were studied using OM, SEM/EDS, tensile test, weight loss test, and electrochemical test. The experimental results showed that Sn addition effectively refined grains and intermetallic phases and increased the amount of intermetallic phases. Meanwhile, Sn addition to the alloys suppressed the formation of the (Mg,Al)2Ca phase and resulted in the formation of the ternary CaMgSn phase and the binary Mg2Sn phase. The Mg-7Al-1Ca-0.5Sn alloy exhibited best tensile properties at room temperature, while Mg-7Al-1Ca-1.0Sn alloy exhibited best tensile properties at elevated temperature. The corrosion resistance of studied alloys was improved by the Sn addition, and the Mg-7Al-1Ca-0.5Sn alloy presented the best corrosion resistance. Keywords
corrosion resistance, die-cast, magnesium alloys, microstructure, tensile properties
1. Introduction Magnesium alloys have been widely used as lightweight structural materials in aerospace and transportation fields due to their higher specific strength, excellent castability, and moderate corrosion resistance (Ref 1-3). Mg-Al-based alloys in particular have extensive applications because of their better die castability and lower cost compared to Mg-RE or Mg-Zn based alloys (Ref 4). However, poor elevated-temperature strength of Mg-Al-based alloys still limits their structural applications (Ref 5, 6). It has been demonstrated that alloying with additional metal components can effectively improve mechanical properties of magnesium alloys (Ref 7, 8). For example, Ca and Sn elements have been used to increase the heat resistance of Mg-Al alloys—these two metals have been shown to exhibit beneficial alloying effect while maintaining low costs. It has been suggested that the addition of Ca can significantly improve the thermal stability and creep resistance of Mg-Al alloys. This change occurs because of the precipitation of heat-resistant intermetallic phases as well as the decrease in the Mg17Al12 phase (Ref 9, 10). Hirai et al. (Ref 11) have reported a drastic decrease in grain size when the amount of Ca in the alloy was increased up to 1.0 wt.%. The Ca addition could also improve the corrosion resistance of AZ91 alloy because of the decrease in Mg17Al12 content and the change of Mg17Al12 morphology (Ref 12). Furthermore, the Ca addition could provide an ignition proof effect during the melting of magnesium alloy (Ref 13), which is beneficial when manufacturing components
Feng Wang, Haikuo Dong, Shijie Sun, Zhi Wang, Pingli Mao, and Zheng Liu, School of Materials Science and Engineering, Shenyang University of Technology, Shenyang 110870, China. Contact e-mails: [email protected]
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