Effects of Ag content on the solid-solution and age-hardening behavior of a Mg-5Sn alloy

Effects of Ag content (0-2 wt%) on the solid-solution and ageing behavior of a Mg-5Sn alloy were investigated. In the solution-treated state, addition of 0.5 wt% Ag can clearly improve the hardness of the Mg-5Sn alloy, while further additions of Ag increase the hardness only a little. On contrary, the age-hardening response of the Mg-5Sn alloy is enhanced proportionally with the amount of Ag added. The microstructure of the peak-aged Mg-5Sn-xAg (x = 0, 0.5, 1, 2) alloys are mainly composed of alpha-Mg matrix and Mg2Sn precipitates. TEM results show that as the Ag additions increase, the number density of the Mg2Sn precipitates increase and the aspect ratio is also reduced, which mainly account for the improved precipitation-hardening response. Retained Ag atoms in alpha-Mg solid solutions also contribute to the strengthening effect in the peak-aged state. Minor blocky Mg54Ag17 particles were observed in the Mg5Sn-2Ag alloy. The particles adopt an orientation relationship of [1 2 0](p)//[1 0 -1 0](alpha), (0 0 2) (p)//(0 0 0 2)(alpha) with respect to alpha-Mg matrix. The role of Ag during the precipitation process has also been discussed. (C) 2016 Elsevier B.V. All rights reserved.