Alloy Composition Design Of Heat Dissipating Mg-Ce/La-Zn Alloys Based On Thermodynamic Calculation

Magnesium alloys derive their mechanical properties from second phase strengthening mechanisms,while these intermetallic compounds are detrimental to their thermal conductivities.The mechanism that causes above-mentioned contradiction is unclear at present:how the types and contents of intermetallic compounds influence the thermal conductivities of Mg alloys and what restricts the development of heat dissipating Mg alloys with high performance.Mg-Ce/La-Zn alloys are considered as tremendous potential heat dissipating materials,whose intermetallic compounds in Mg-rich corner have significant influence on the heat dissipation performance of Mg alloys.Although there have been serveral reports about types of intermetallic compounds and the phase equilibria among these phases in Mg-rich region of Mg-Ce/La-Zn systems,whether phase?₁-?Ce/La?_0.077?Mg,Zn?_0.923is different from REMg₁₂ is still controversial.Figuring out the relationships between intermetallics compounds and thermal conductivity is of vital importance to develop new type of magnesium alloys with both good heat dissipation performance and mechanical properties.In this paper,phase equilibria relationships of Mg-Ce-Zn system are re-assessed using equilibriated alloy method.Combining with CALPHAD method,thermodynamic description of Mg-Ce-Zn system is optimized.The thermal diffusivity of alloy is measured by laser flash method,and the thermal conductivity is calculated by multiplying the specific heat capacity,density and thermal diffusivity.In addition,phase constituent and the solid solubility of Zn in?-Mg are predicted through calculation of solidification path in order to design the heat dissipation alloys.And it helps analyze the effects of intermetallic compounds and solid solubility on the thermal conductivities of the alloys.The main conclusions are as follows:?1?Ternary phase?₁-?Ce?_0.077?Mg,Zn?_0.923and binary phase CeMg₁₂ exist in the Mg-Ce-Zn system.Crystallographic parameters of?₁ are determined by XRD structural analysis,which are resolved as space group of Cmc21 with a=0.9852?2?–1.0137?2?nm,b=1.1361?3?–1.1635?3?nm and c=0.9651?2?–0.9989?2?nm.Both?₁ and REMg₁₂in Mg-rich corner of Mg-Ce/La-Zn system equilibrate with phase?-Mg.?2?Comparing the effects of different intermentallic compounds on thermal conductivities of Mg alloys,thermal conductivities of dual-phase Mg-Ce/La-Zn alloys containing phase?₁ are lower than those with REMg₁₂ at the same temperature.And thermal conductivities decrease with increase of the content of intermetallic compounds.However,Mg alloys with La have better thermal conductivity than those with Ce.Mg-2.4 mol%La Mg₁₂exhibits the highest thermal conductivity,154.2 W/m·K at 323 K and157.6 W/m·K at 523 K.Similarly,Mg-2.2 mol%CeMg₁₂has upper thermal conductivity,129.4 W/m·K at 323 K and 138.4 W/m·K at 523 K.When alloys with the same type and content of intermetallic compounds,the solid solubility of Zn element in?-Mg,causing lattice distortion,make thermal conductivity decline sharply.And the thermal conductivity decreases by 4%when Zn solid solubility increases by 0.4 at.%.Mg-La-Zn alloy with 6.7 mole%?₁-?La?_0.077?Mg,Zn?_0.923and 1.54 at.%Zn solid solubility in?-Mg possesses thermal conductivity up to 123.0 W/m·K at 323 K and136.7 W/m·K at 523 K.?3?Condersing the tensile mechanical strength and the thermal conductivity of Mg alloys,the range of compositions for Mg-Ce/La-Zn alloys are optimized.In Mg-Ce/La-Zn system,Mg-?0.17?0.57 at.%?La-?1.53?2.38 at.%?Zn and Mg-?0.14?0.52at.%?Ce-?1.60?2.02 at.%?Zn have both good heat dispersion performance and tensile property,whose thermal conductivity,yield strength and elongation are higher than120 W/m·K,85 MPa and 5%,respectively.