| Human society is currently facing challenges in resources and the environment.For the better survival of mankind in the future,countries all over the world are seeking a path of sustainable development.As an engineering material,magnesium alloy has many advantages.The reserves of Mg element on the earth are very abundant,and it is easy to be recycled for environmental protection.Therefore,magnesium alloy is known as"21st Century Green Engineering Material".With the development of the electronic industry,the problem of heating of electronic components has led to higher requirements for the heat dissipation and thermal expansion performance of electronic packaging materials,that is,higher thermal conductivity,lower thermal expansion coefficient and certain mechanical properties.Pure magnesium has good thermal conductivity,and its good electromagnetic shielding properties make magnesium alloys very suitable for the stability of electronic equipment.However,the current commercial magnesium alloys are still difficult to meet the requirements,so it is necessary to develop a new type of low-expansion and high thermal conductivity magnesium alloy.Broaden the application of magnesium alloys.In this paper,the Mg-Zn-Cu series alloy is the research object,and the influences of the preparation process,alloy composition and heat treatment process on the alloy structure,thermal properties and mechanical properties are studied.The Mg-2.5Zn-2.5Cu-0.4Zr(x=2.5?3.3?4.1?4.9)alloy was prepared by gravity casting and squeeze casting processes,and its structure was observed and its properties were tested.Squeeze casting alloys are denser than gravity casting alloys,with higher thermal conductivity and tensile strength,but lower thermal expansion performance.Considering comprehensively,the Mg-2.5Zn-x Cu-0.4Zr alloy was prepared by squeeze casting,and the effect of Cu content on the alloy at 2.5 wt.%,3.3 wt.%,4.1 wt.%and 4.9 wt.%was studied.Organization and performance impact.As a result,with the increase of Cu content,the eutectic network structure becomes denser,and the scattering effect of electrons and phonons is enhanced,so that the thermal conductivity of the alloy decreases,and the thermal conductivity decreases from 132.7W/(m·K)to 121.1 W/(m·K).Because the grain boundary is relatively brittle and cannot resist deformation well,the mechanical properties are reduced.The grain boundary will limit the expansion of the matrix,the network structure will become dense,the restriction on the expansion of the matrix will be enhanced,and the thermal expansion coefficient will decrease.The average thermal expansion coefficient is at least22.68×10-6 K-1.The Mg-5Zn-x Cu-0.4Zr(x=2.5?3.3?4.1?4.9)alloy was prepared by squeeze casting,which has a higher Zn content.The influence of Cu content on its performance is also different from that of Mg-2.5Zn-x Cu-0.4Zr.With the increase of Cu content,the Mg Cu Zn phase with good thermal conductivity increases,consuming Zn atoms in the matrix,reducing the lattice distortion of the alloy,and improving the thermal conductivity more than the scattering of electrons and phonons by the mesh grain boundary.The effect of reducing the thermal conductivity,so that the thermal conductivity of the Mg-5Zn-x Cu-0.4Zr alloy gradually increases from 130.3 W/(m·K)to 141.4 W/(m·K).The increase in the amount of hard and brittle network grain boundaries strengthens the restriction on the expansion of the matrix and reduces the thermal expansion coefficient of the alloy.The minimum thermal expansion coefficient is 22.01×10-6 K-1.The effects of T1 heat treatment and T6 heat treatment on alloy structure and thermal properties are studied.T1 heat treatment hardly changes the morphology of the alloy,but T1heat treatment can eliminate the residual stress of the material and reduce the dislocation density,and the thermal conductivity and thermal expansion properties of the alloy are improved.T6 heat treatment has undergone a higher temperature solution treatment,and the structure of the alloy has changed significantly.The thermal conductivity of the alloy is greatly improved,while the thermal expansion performance is slightly reduced.Finally,the squeeze casting Mg-5Zn-x Cu-0.4Zr is subjected to T6 heat treatment(solid solution at 430°C for 24h+aging at 180°C for 24h),and the maximum thermal conductivity of the alloy at a Cu content of 4.9wt.%is 147.9W/(m·K),the average thermal expansion coefficient of the alloy at 293K?373K is 23.34×10-6 K-1. |
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