Effects Of Zn Addition And Heat Treatment On The Microstructure,Thermal And Electrical Conductivity Of Mg-4Y Alloys

With the development of light,thin,short and small telecommunication products,people have higher requirements for the selection of many electronic product shell materials and heat sink materials.On account of their low density as well as excellent thermal and electrical conductivity and electromagnetic shielding,magnesium alloys are good candidates for heat dissipation materials in 3C products.On the basis of researches on high conductivity Mg-Zn,Mg-RE alloys,the Mg-4Y alloys with different Zn?1⁴ wt.%?content was selected in this paper.By using optical microscope,X-ray diffractometer,differential scanning calorimeter,scanning electron microscope and energy spectrometer,eddy current conductivity meter,LFA 457 laser thermal conductivity meter and so on,the effects of Zn content,solid solution and aging on microstructures,thermal and electrical conductivity of alloys were systematically investigated.The main conclusions were summmarized as follows:With Zn contents increases from 1%to 4%,the ternary phase of as-cast Mg-4Y-xZn alloys gradually changes from the X,X phase to X+W phase and W phase.With the addition of Zn increased,the grain size of alloys firstly increased and then reduced,and the grain size of alloys with 3%Zn is39.2?m.The thermal and electrical conductivity of alloys do not linearly increase with the increase of Zn,but follow the tendency of WZ41<WZ43<WZ42<WZ44.The obtained highest room temperature thermal and electrical conductivity of the WZ44 alloy are 13.73 MS·m^-1 and 95.61 W·m^-1·K^-1,respectively.On the basis of the Smith–Palmer equation,the correlation between the electrical conductivity and the thermal conductivity of Mg-4Y-Zn alloys at 298 K was characterized.The Lorentz number L'was amended to 2.1895×10^-8·V²·K^-2 and the lattice thermal conductivity was 6.70W·m^-1·K^-1.The solution treatment process of WZ41^WZ43 alloys was finally determined to be 530°C×10 h,and WZ44 alloy was 500°C×13 h.After T4 treatment,the Mg₂₄Y₅ phase was found with higher Zn content in addition to?-Mg+X?W?phase.After T6 treatment,the precipitated phase mainly included MgZn,MgZn₂ and Mg₂₄Y₅ phases.As the aging time increases,second phases in alloys gradually changed from dispersion particles to thin rod-like and irregular blocks.Meanwhile,Mg-Zn precipitates gradually changed from Mg₇Zn₃ phase to MgZn₂ phase and more stable MgZn phase.The grain gradually growth up with the increase of the aging time,and the grain is 65.94?m when the aging time increases to 120 h.After T4 treatment,the amount of Zn and Y solid solution atoms in the?-Mg matrix increases,caused the thermal and electrical conductivity of alloys decreased.After T6 treatment,the precipitation of MgZn and Mg₂₄Y₅ phases,and the more uniform structure were benefit to improve the thermal and electrical conductivity.Therefore,the thermal conductivity and electrical conductivity of Mg-4Y-xZn alloys in different states are in the form of T4<cast state<T6.When the aging time fixed to be 12 h,the thermal and electrical conductivity of WZ44 alloy increase gradually with the aging temperature?175°C,200°C,225°C,250°C?and the growth rate gradually slows down.The thermal and electrical conductivity at 250°C are 103.54 W·m^-1·K^-1 and15.49 MS·m^-1,respectively.When the aging temperature fixed to be 225°C,the thermal and electrical conductivity of the alloy increases rapidly and then slowly increased.After 120 h of aging,the thermal conductivity and electrical conductivity of the alloy increases to 112.25 W·m^-1·K^-1and 16.573 MS·m^-1.The thermal conductivity of T6 WZ44 alloy increased with the increase of working temperature?25¹50°C?,and the thermal conductivity of the alloy at 150°C is increased by 8%compared with the alloy at room temperature,and reaching to 111.86 W·m^-1·K^-1.