Lowering thermal expansion of Mg with the enhanced strength by Ca alloying

Abstract

The influence of Ca on the thermal expansion and mechanical properties of Mg are investigated in the present work. Alloying Ca is demonstrated to noticeably decrease the coefficient of thermal expansion (CTE) within a wide temperature interval and increase the strength of Mg at both as-cast and extruded state. A low CTE of ∼18.6 × 10−6 K−1 in combination with the high compressive yield strength of 262 MPa are achieved within the studied concentration interval. The reduced CTE of Mg–Ca alloys is found to closely correlate with the increased Debye temperature with Ca, which primarily emerges from the increased precipitation of Mg2Ca phase showing the relatively high melting point, elastic/shear moduli and low CTE. Similarly, the increased fraction of the eutectic lamellar structure consisting of Mg2Ca and α-Mg dominates the noticeable increase of strength of the as-cast Mg–Ca alloys. The lamellar structure is broken into fine particles dispersing in the matrix at extruded state, which in combination with the refined microstructure yields the dominated contribution to the increment of strength. The low thermal expansion and high strength achieved in the designed Mg–Ca alloys provide a feasible route for the development of advanced Mg alloys.