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 Mg2Sn phase. The creep resistance of aged Mg-7Sn alloy is poor. The addition of Si and Al to Mg-7Sn alloy has resulted in improving the creep resistance due to the refinement of Mg2Sn phase and the appearance of Mg2Si phase at the grain boundaries. The Mg-7Sn-1Si alloy exhibits better creep resistance at 200 °C than Mg-7Sn-5Si and Mg-7Sn-5Si-2Al alloys. The Mg-7Sn alloys with 5% Si have better creep properties at 250 °C in comparison to Mg-7Sn-1Si alloy.
Highlights
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, intensive research is being carried out to improve the creep resistance of magnesium alloys
The low creep resistance of Mg alloys containing up to 5% Sn is the result of the formation of large precipitates of the equilibrium Mg2Sn phase, their unfavorable crystallographic orientation relative to the α-Mg matrix, tendency to coagulate at elevated temperature and the lack of strengthening of grain boundaries
Summary
Magnesium alloys due to their low density are attractive materials for the aerospace and automotive industries [1]. 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. Silicon—that forms the Mg2Si phase in magnesium alloys—is one of the alloying elements that can favorably affect the creep resistance of magnesium alloys at low manufacturing costs. Research to modify the shape and size of primary crystals has not contributed to significant improvements in mechanical properties of Mg-Si alloys containing
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