摘要
以Al-4.8Cu合金为基体,通过加入稀土元素La,研究其对合金组织形貌、力学性能以及热导率的影响。采用光学显微镜(OM)、扫描电镜(SEM)、X射线衍射(XRD)、万能拉伸试验机、热传导系数测量仪等分析手段,并结合第一性原理进行表征。结果表明,随着La元素含量的增加,晶粒形貌由树枝晶向等轴晶转变,晶粒尺寸减小,当La元素的含量为0.38%时晶粒的细化现象较为明显,晶粒平均尺寸由不含La元素时的149μm降至69μm。随着La元素含量的增加,合金的抗拉强度、屈服强度、延伸率和热导率呈现先增大后减小的趋势,La元素含量为0.38%时,合金的抗拉强度、屈服强度达到最大,分别为175.69 MPa和115.20 MPa;La元素含量为0.29%时,合金的延伸率达到最大,为10.04%;La元素含量为0.78%时,合金的热导率达到最大,为210.70 W·m^(-1)·K^(-1),相比未添加La元素时分别提升了43.9%,43.5%,60.9%和10.3%。La元素加入过量后产生的Al4La,Cu5La相会对合金的力学性能和热导率产生较大危害。
In the era of rapid development of electronic information technology,the power per unit area of integrated circuit increases,resulting in heat concentration,prone to thermal damage of components caused by excessively high regional temperature.The thermal conductivity of pure aluminum is excellent,but the addition of other alloying elements will decrease the thermal conductivity of pure aluminum in most cases.Therefore,how to balance the thermal conductivity and mechanical properties of aluminum alloy is an urgent problem to be solved.Aluminum-copper alloy is called duraluminium alloy,which has simple casting process,good cutting perfor⁃mance and mechanical properties.Rare earth element La was added to Al-4.8Cu alloy to adjust its structure and phase content in this paper,so as to achieve a balance between thermal conductivity and mechanical properties,and further expand its application field.To prepare Al-4.8Cu-0.15Ti-XLa alloy,pure Al and Al-Cu alloy were first melted in a resistance furnace at 730℃,and then Al-Ti alloy and Al-La alloy were added and the melt was kept warm.After refining at 720℃,the melt temperature was adjusted to 700℃and poured into a metal mold at 250℃.The microstructure and properties of the alloy were characterized by optical microscope(OM),scanning electron microscope(SEM),X-ray diffraction(XRD),universal tensile testing machine and thermal conductivity measuring instrument.The properties of some phases in the alloy were calculated based on first principles.When 0.38%La element was added to the alloy,the grain size of the alloy was equiaxed,most of the dendrites had been fused and disintegrated,and the grain size reached the minimum.Compared with the 149μm without La element,the grain size decreased by 53.7%.After adding La element to Al-4.8Cu alloy,Al20Ti2La phase was formed in the alloy,which precipitated beforeα-Al in the solidification process.The lattice mismatch be⁃tween Al20Ti2La phase andα-Al matrix could be calculated as 4.11%.The results showed that Al20Ti2La phase could be used as hetero⁃geneous nucleation point to refineα-Al matrix.When the La content was 0.38%,the tensile strength and yield strength of the alloy reach the maximum,which were 175.69 MPa and 115.20 MPa,respectively.When La content was 0.29%,the elongation reaches the maximum of 10.04%.The thermal conductivity of the alloy with 0.78%La element reached the maximum of 210.70 W·m^(-1)·K^(-1),which increased by 43.9%,43.5%,60.9%and 10.3%,respectively,compared with that without La element.In the absence of La element,there was almost no low melting point phase in the intergranular cracks of alloy.After adding La element,a certain amount of intergran⁃ular liquid film appeared,but the strength was low,and it was easy to be torn by the intergranular separation stress.When the number of liquid film was enough,the liquid film would only be stretched and would not be torn,which significantly improved the mechanical properties and thermal conductivity.However,with the further increase of La content,Al4La phase would converge at the grain bound⁃ary during solidification,causing harm to the mechanical properties and thermal conductivity of the alloy.The porosity in the alloy had great harm to the mechanical properties and thermal conductivity.By calculating the ratio of the actual density to the ideal density,it was found that the ratio increased with the increase of La content,indicating that the volume fraction of the porosity in the alloy de⁃creased.First,La element could react with O,H and other elements entering the melt during smelting to form compounds with high melting point,such as LaH2,La2O3,etc.,and the melt was discharged in the slag raking process.In addition,the addition of La ele⁃ment could shorten the solidification temperature range and make the solidification mode transition from paste solidification to sequen⁃tial solidification.Moreover,the addition of La element could increase the low melting point phase in the alloy,which played a good role in filling the intergranular pores caused by the intergranular separation stress.The decrease of the pores in the alloy would greatly improve the mechanical properties and thermal conductivity.The equilibrium distribution coefficient of Cu at the solidification inter⁃face decreased with the increase of La element,so the decrease of Cu atoms in theα-Al matrix also increased the thermal conductivity of the alloy.It was generally believed that the higher the Debye temperature of the material,the higher the strength of the chemical bond and the better the thermal conductivity.By calculating the Debye temperatures of Al2Cu,Al11La3,Al4La and Cu5La phases,it could be seen that the Debye temperature of Al11La3 phase was higher than that of the other three phases.Therefore,the Al11La3 phase formed by adding La element to the Al-4.8Cu alloy was beneficial to the improvement of the strength and thermal conductivity,while the Al4La and Cu5La phases formed by adding too much La would reduce the mechanical properties and thermal conductivity of the alloy.
作者
宋赵熙
李元东
刘文憬
杨昊坤
曹杨婧
毕广利
Song Zhaoxi;Li Yuandong;Liu Wenjing;Yang Haokun;Cao Yangjing;Bi Guangli(State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metals,School of Materials Science and Engineering,Lanzhou University of Technology,Lanzhou 730050,China;Key Laboratory of Non-Ferrous Metal Alloys and Processing,Ministry of Education,Lanzhou University of Technology,Lanzhou 730050,China)
出处
《稀有金属》
EI
CAS
CSCD
北大核心
2024年第6期786-795,共10页
Chinese Journal of Rare Metals
基金
甘肃省自然科学基金项目(22JR5RA251)
国家重点研发计划项目(2018YFB2001800)资助。
关键词
铝合金
La元素
热导率
力学性能
第一性原理
aluminum alloy
La element
thermal conductivity
mechanical properties
first principle
