The microstructure and creep properties of as-cast Mg-Sn-Si-(Al) magnesium alloys
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ORIGINAL ARTICLE
The microstructure and creep properties of as‑cast Mg‑Sn‑Si‑(Al) magnesium alloys Tomasz Rzychoń1 Received: 25 January 2020 / Revised: 21 July 2020 / Accepted: 30 July 2020 / Published online: 8 August 2020 © The Author(s) 2020
Abstract Magnesium alloys containing rare earth metals exhibit good creep resistance up to 300 °C and good tensile properties at ambient temperature. The high cost of rare earth has led to studies regarding the creep resistance of Mg alloys with cheap alloying elements (Sn, Ca, Si) that could be substituted for Mg-RE alloys. In this paper, the influence of Si and Al on microstructure and mechanical properties of Mg-7Sn alloy was investigated using optical (LM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), tensile tests and creep tests at 200–250 °C. Microstructure of as-cast alloys consists of α-Mg matrix and intermetallic compounds at the interdendritic regions. Heat treatment consisting of solid solution treatment and ageing increases the tensile properties at ambient temperature due to the precipitation of the fine M g2Sn phase. The creep resistance of aged Mg-7Sn alloy is poor. The addition of Si and Al to Mg7Sn alloy has resulted in improving the creep resistance due to the refinement of M g2Sn phase and the appearance of M g2Si phase at the grain boundaries. The Mg-7Sn-1Si alloy exhibits better creep resistance at 200 °C than Mg-7Sn-5Si and Mg-7Sn5Si-2Al alloys. The Mg-7Sn alloys with 5% Si have better creep properties at 250 °C in comparison to Mg-7Sn-1Si alloy. Keywords Magnesium alloys · Mg-sn alloys · Mg-si alloys · Microstructure · Creep properties
1 Introduction Magnesium alloys due to their low density are attractive materials for the aerospace and automotive industries [1]. Commercial Mg–Al alloys are characterized by low operating temperature (up to about 120 °C), thus intensive research is being carried out to improve the creep resistance of magnesium alloys. Increase in creep resistance of Mg–Al alloys is achieved by introducing alloying elements such as silicon [2, 3], strontium [4], calcium [3, 5] and rare earth metals [6]. These alloys can be operated up to a temperature of about 200 °C. In the last two decades, the Al-free magnesium alloys with rare earth metals, yttrium, strontium and manganese (Mg-Zn-RE, Mg-Y-Nd-Zr, Mg-Sr-Mn, and Mg-Nd-GdZr) have been developed, which can be used for structural elements operating up to a temperature of 250 °C (even up to 300 °C during short-term operation) [7–9]. In the case of Al-free magnesium alloys good creep properties are related * Tomasz Rzychoń [email protected] 1
Faculty of Materials Science, Silesian University of Technology, Katowice, Poland
to the presence of the strengthening phases characterized by good thermal stability at elevated temperatures. However, these alloys are expensive due to the high cost of rare earth metals and also in some cases technological problems in casting. Thus, there is a need for an alternative
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