Insights into the microstructures and mechanical properties of magnesium–calcium–transition elements: A combined experimental and simulation study

Abstract

Small amounts of transition elements: Ti, Mn, Fe, Co, and Ni, have been added to a Mg–0.1Ca (wt%) alloy to elucidate their additions on the microstructure and room temperature (RT) mechanical properties. Only Ni was effective in weakening the texture intensity and thus led to the improvement in RT formability and ductility, whereas the other elements were basically no effect. The microstructural characterization by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) in conjunction with energy-dispersive X-ray spectrometry (EDS) and numerical simulation using a grain boundary (GB) phase model indicates that the Ca and Ni co-segregated to the GB of the Ni-containing alloy, while the GB of the other alloys was enriched with Ca only. Further investigations by a correlative electron backscatter diffraction and STEM-EDS reveal that the transverse direction (TD) oriented GBs had significantly lower concentration of Ca and Ni compared to the basal-oriented GBs, which resulted in the development of the TD-split texture in the Ni-containing alloy. A compositionally optimized Mg–0.1Ca–0.1Ni (wt%) alloy showed a large index Erichsen value of 8.5 mm in the sheet form, and exhibited a high tensile yield strength of 238 MPa with a moderate fracture elongation of 14% in the form of an extruded rod. Due to the addition of small amounts of alloying elements, the newly developed Mg–0.1Ca–0.1Ni alloy had an excellent thermal conductivity of 154 W/(m·K) which is even higher than that of a commercial 5052 Al alloy.