Study On Thermal Conductivity Of Mg-6Zn-xCe Alloy

With the development of electronic communication and aerospace industry,new equipment which has high-precision,high-power,and miniaturized puts higher demands on the lightweight and thermal conductivity of materials.The unbalanced development of thermal conductivity and mechanical properties of existing thermal conductive magnesium alloys has seriously hindered the application of magnesium alloys in the engineering field with dual mechanical and thermal conductivity requirements,and it is urgent to develop new magnesium alloy materials with high thermal conductivity.In this paper,the Mg-Zn-Ce alloy system was selected as the research object,and four kinds of Mg-6Zn-xCe alloys(x=0,0.5,1.0,1.5 wt.%)were designed and then the alloy was smelted and prepared.The effects of composition,heat treatment and cooling methods on the microstructure and thermal conductivity of the alloy were systematically studied by means of optical metallographic microscope,X-ray diffractometer,scanning electron microscope,energy spectrometer,transmission electron microscope and laser thermal conductivity meter.This study will provide theoretical basis and data support for the development of high performance,low cost,structurally functional integrated magnesium alloys.The effect of the composition on thermal conductivity was investigated.In the as-cast water-cooled alloy,the main phase composition of Mg-6Zn alloy is ?-Mg and Mg7Zn3 phase.After adding Ce element,the new phase Ce5(Mg,Zn)41 appears in the alloy,and it increases with the increase of Ce content.The formation of the Mg7Zn3 phase is inhibited.The volume fraction of eutectic structure increases with increasing Ce content,and its continuity is enhanced.The thermal conductivity of the as-cast alloy decreases with increasing Ce content.The effect of heat treatment on thermal conductivity was investigated.After solution treatment,Mg7Zn3 phase is dissolved back in the alloy,and the Zn atom in the Ce5(Mg,Zn)41 phase is dissolved back,and the phase species is transformed into Mg,7Ce2 phase,which is intermittently distributed in the grain boundary.After aging treatment,the supersaturated Zn atoms in the matrix are precipitated in the form of MgZn phase and traces of MgZn2 phase,and the second phase is still Mg17Ce2 phase.Compared with the thermal conductivity of the alloy,the aging state>the as-cast state>the solid solution state.The thermal conductivity of the alloy in the three states decreases with the increase of the Ce content.The effect of cooling way on heat conduction was investigated.The water-cooled alloy and ice-water-cooled alloy have fine crystal grains,and there is a chilling zone on the outermost side of the ingot.The air-cooled and liquid nitrogen-cooled alloy grains are coarse,and the microstructure of the ingot is similar at different positions.The second phase of the four alloys is the Ce5(Mg,Zn)41 phase.The water-cooled alloy and ice-water-cooled alloy ingots have the highest thermal conductivity at 1/2 radius of the ingot,and the other two positions have relatively low thermal conductivity.The closer the air-cooled alloy and liquid nitrogen-cooled alloy are to the core of the ingot,the lower the thermal conductivity.The thermal conductivity of the ice-water-cooled alloy and the water-cooled alloy is better than the other two alloys as a whole,and an appropriate increase in the cooling rate during the cooling process of the ingot can increase the thermal conductivity of the alloy.