Microstructure and Mechanical Properties of a Ag Micro-Alloyed Mg-5Sn Alloy
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JMEPEG https://doi.org/10.1007/s11665-018-3433-4
Microstructure and Mechanical Properties of a Ag Micro-Alloyed Mg-5Sn Alloy S.H. Huang (Submitted October 13, 2017; in revised form March 17, 2018) Effects of 1.5 wt.% Ag addition and solid solution + artificial ageing at 160 °C on the microstructure and mechanical properties of a Mg-5Sn alloy have been studied. The results show that Ag addition has significantly hardened the solution-treated Mg-5Sn alloy. During the ageing process, the hardness increase rate and the strength and ductility of the Mg-5Sn alloy at each state are also improved by Ag addition. The improved strengthening behavior is primarily attributed to the refinement distribution of the Mg2Sn precipitates, the enhanced precipitation process, and the synergistic strengthening effect of Mg2Sn and a metastable plate DO19 phase formed at lower ageing temperature. For each solution-treated alloy, the strength and ductility are higher than the corresponding cast ones. Ageing further enhances the yield strength, and the ductility of the Mg-5Sn-1.5Ag alloy is also increased after ageing. The fracture surfaces of the both peak-aged alloys exhibit the characteristic of a mixture of quasi-cleavage and ductile fracture. Keywords
age hardening, Mg-Sn alloy, micro-alloying, precipitation, tensile properties
1. Introduction Among various strengthening methods of alloys, precipitation strengthening is an effective and practical way for many Mg alloys. The major alloying elements of Mg alloys such as Al, Zn, RE, and Sn all have a large solid solubility in Mg matrix, and the solubility decreases considerably with decrease of the temperature (Ref 1), which provides a good condition for the precipitation strengthening. The detailed precipitation sequence and crystallographic features of the precipitates in these typical age-hardening Mg alloys have been well summarized in recent reviews (Ref 2, 3). Mg-Sn alloys is one group of the typical precipitation-strengthening alloys which have good potential for application in elevated temperature conditions due to the high melting point of the Mg2Sn precipitates and the high eutectic temperatures (Ref 4, 5). Therefore, Mg-Sn alloys have aroused considerable concern in recent years. In addition to their application in the cast state, Mg-Sn alloys also have great potential for use as wrought alloys (Ref 6-8). A common way to strengthen wrought alloys is artificial ageing treatment after deformation of the solid-solution-treated alloys. In order to improve the age-hardening response of Mg-Sn alloys, various micro-alloying elements have been added to the alloy, and a good enhancing effect has been obtained (Ref 9-13). Ag is one of the effective micro-alloying elements because it can form solute clusters before the precipitation of Mg2Sn, thus acting as an effective heterogeneous nucleation sites for the precipitates. As a result, the Mg2Sn precipitates can be refined significantly and the strengthening effect is improved remarkably (Ref 14). Usually, artificial ageing treatment of most M
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