Effect of Ag and Cu trace additions on the microstructural evolution and mechanical properties of Mg–5Sn alloy

• Mg–5Sn alloy has been modified with trace additions of Ag (0.175%) and Cu (0.035%).
• Microstructural, mechanical, thermal stability and corrosion properties are investigated.
• Trace Ag and Cu modified the second-phase morphology and formed additional nanophases.
• Addition of both Ag and Cu changed the strong basal texture of the Mg–5Sn alloy.
• Both Ag and Cu reduced corrosion rate, improved thermal stability and tensile ductility.

In this study, the effect of trace additions of Ag (0.175 wt.%) and Cu (0.035 wt.%) on the microstructural evolution and mechanical behavior of extruded Mg–5Sn alloy is investigated. Microstructural studies revealed that all the alloys have fine grains (2–6.5 μm), and that the binary Mg–5Sn alloy has polygonal and submicron-sized lath/rod-like Mg2Sn second phase particles. While Ag addition (TQ50 alloy) induced a change in morphology from lath/rod-shaped Mg2Sn to short-rod/oblong-shaped Mg–Sn–Ag particles, the presence of Ag and Cu (TQC500 alloy) resulted in an additional Mg2(Cu, Sn) nano-sized phase. From XRD analyses, it was identified that the trace addition of Ag and Cu modified the preferred Mg-crystal orientation of the Mg–5Sn alloy that had basal planes strongly aligned parallel to the extrusion direction. Both Ag and Cu contributed to a remarkable decrease in the coefficient of thermal expansion and better static salt–water corrosion resistance. When compared to pure Mg, all the alloys showed significant improvement in hardness, tensile and compressive strength values, with Ag and Cu trace additions contributing to enhanced tensile ductility. The effect of trace additions of Ag and Cu on the material behavior was identified based on structure–property correlation.