Advanced wrought Mg-4.5Al-2.5Ca-0.02Mn (at%) alloys with exceptional balance of high thermal conductivity, yield strength, ductility, nonflammability, and corrosion resistance

Abstract

Advanced wrought Mg-Al-Ca-Mn alloys were developed, demonstrating an outstanding array of technical advantages due to the remarkably high negative mixing enthalpy of an Al and Ca pair. This was achieved through meticulous optimization of alloy composition, heat treatment procedures, and extrusion parameters. The primary alloy under consideration was designated as Mg-4.5Al-2.5Ca-0.02Mn (at%). While maintaining a low density of 1.76 g/cm3, this alloy exhibited an exceptional properties profile, comprising a high thermal conductivity up to 124 Wm−1K−1 (approximately 79% of pure magnesium), a high tensile yield strength of 397 MPa (surpassing the high-strength aluminum alloy 7075-T6, by 25% in specific tensile yield strength), a notable tensile elongation of 5.5%, and remarkable nonflammability with a high ignition temperature of 1355 K. Finally, its corrosion resistance was twice that of the AZ91D alloy. The microstructure of the developed alloy system comprised α-Mg, eutectic C36 and C14 compounds, and precipitated C15 compound. The enhanced thermal conductivity was attributed primarily to the purification of the α-Mg matrix, facilitated by C15 plate precipitation during the heat treatment process. The superior mechanical properties were associated with the refinement of the α-Mg phase grain structure and the uniform dispersion of fine compounds achieved through extrusion. Based on the findings derived from this experimental study, a novel approach to designing multifunctional magnesium-based alloys has been formulated; that is, high thermal conductivity and high strength are attainable in plastically deformed Mg alloys composed of element pairs with a negatively high mixing enthalpy.