Effects of Sn addition on dynamic grain growth in a binary Mg-1Ca alloy

The possibility of dynamic grain growth of a binary Mg-1Ca alloy with minor tin contents was investigated at various conditions of temperature and strain rate. Mg-1Ca, Mg-1Ca-1Sn and Mg-1Ca-2Sn alloys were cast and homogenized at 410 degrees C followed by hot-rolling at 400 degrees C with equal strains. Calcium contributed to refining of grains, with an additional support from tin. In the as-cast alloys, tin was found to promote dendrite formation. Though presence of Ca2Sn phase was predicted by thermodynamic modelling, microstructurally a ternary phase MgCaSn was predominantly found. This ternary phase was also comparatively coarser in size. Uniaxial tensile test of rolled samples was carried out at temperatures 300, 350, 400 and 450 degrees C, and at two different strain rates 5 x 10(-4) s(-1) and 1 x 10(-4) s(-1). Variation of grain distribution was also measured at the grip and gauge regions at different locations. Samples were taken from six different locations of the deformed samples. Even at faster deformation, the grains were not elongated. At slower strain rate condition, extent of dynamic grain growth was higher compared to that of the higher strain rate condition. Mg2Ca particles were not effective in restricting movement of grain boundaries. Mg2Sn particles were dissolved in the matrix at the elevated temperatures, and the grain growth limiting was profoundly dominated by the presence of MgCaSn phase.

Automated summary

The study investigated the possibility of dynamic grain growth in a binary Mg-1Ca alloy with minor tin contents. It was found that calcium contributed to grain refinement, while tin supported dendrite formation. A new ternary phase MgCaSn was predominantly observed in the microstructure, limiting grain growth effectively despite the presence of Mg2Ca and Mg2Sn particles in the matrix. Moreover, the extent of dynamic grain growth was higher at slower strain rates compared to higher strain rates during the uniaxial tensile tests.