| Heat-resistant aluminum alloy wires have higher heat resistance and strength than ordinary hard-drawn aluminum wires,and are more and more commonly used in high-voltage power transmission lines.In the meantime,as urban power demands increase,the capacity of transmission lines needs to be expanded urgently and thus wires of higher heat resistance are required.For the existing Al-Zr series of heat-resistant conductive aluminum alloys,the addition of Zr elements significantly reduces their electrical conductivity while increasing their heat resistance temperature,and thus increases the loss of electric energy during transmission.As a result,the heat resistance and electrical conductivity of the wires do not exist simultaneously.Therefore,it is of great significance to study and prepare heat-resistant aluminum alloy wires that have excellent heat resistance and electrical conductivity.It is well known that pure aluminum has good electrical conductivity and AIN is a kind of heat-resistant phase with excellent high temperature mechanical properties and strong thermal stability.The previous research results of the research group show that as a particle strengthening phase,AIN can significantly improve the high temperature mechanical properties of aluminum alloy.In this thesis,two processes are used respectively to prepare AlNp-reinforced aluminum alloy materials.This thesis firstly analyzes the rules of influence of nano AlNp,which are in-suit synthesized,on the tensile properties and electrical conductivity of aluminum alloy,experiments the rules of influence of ageing heat treatments,which are conducted at different temperatures and under different holding time,on the room temperature strength and electrical conductivity of the above-mentioned aluminum alloy,and tests as well as analyzes the heat resistance quality of the optimized alloy.Also,this thesis prepares AINp-reinforced aluminum composites by casting process,investigates the influence of the added reinforcement particles on the tensile properties,electrical conductivity and heat-resistance quality of 1070 conductive aluminum,and proposes a new process to improve the heat resistance and electrical conductivity of the conductive aluminum alloy simultaneously.The main research work of this thesis is as follows:(1)Research on the Tensile Properties and Electrical Conductivity of Aluminum Alloy Materials Reinforced by In-Situ Nano AlNpBy in-situ synthesis method,this thesis prepares aluminum alloy materials(hereinafter referred to as Al-xAlNp),whose mass fraction are 0,0.82%,1.64%and 2.46%respectively.After testing the room temperature mechanical properties and electrical conductivity of the composites,it is found that when AlNp is not contained,the tensile strength of alloy is 120MPa;when the mass fraction of AlNp is 2.46%,the tensile strength of alloy increases to 235MPa and the elongation of alloy decreases from 30.1%to 17.1%;in the meantime,due to the increase of the number of particles in the matrix,the inhibition effect of the movement of the electron current is enhanced,so the electrical conductivity of alloy decreases from 60.9%IACS(International Annealed Copper Standard)to 55.4%IACS.After adding a small amount of C element into the Al-0.14N-0.11B alloy,the micron-sized AlB2 phase in the matrix is transformed into the nano-sized Al3BC phase and the strengthening effect on the alloy is enhanced,so the room temperature ultimate tensile strength of the alloy increases from 174MPa to 193MPa;at the same time,the change of particle size enhances the radiation effect of free electrons,so the electrical conductivity of alloy decreases by 1.8%IACS.(2)Exploration of Ageing Heat Treatment Process of Alloy and Research on Heat Resistance Quality of AlloyThe alloys of Al-0.41AlNp,Al-0.82AlNp and Al-M.64AlNp are ageing at 175?,225 ? and 275 ? under different holding time and the results show that the tensile strength and electrical conductivity of the alloys after ageing heat treatment all have been improved to different degrees.At the same ageing temperature,the strength of the alloys gradually increases and eventually stabilizes with the extension of the ageing time and the electrical conductivity of the alloy gradually increases with the extension of the ageing time.After increasing the ageing temperature,both the electrical conductivity and the tensile strength of the alloys increase.The heat resistance tests of the alloys of Al-0.41AlNp,Al-0.82AlNp and AI-1.64AlNp show that the long-term permissible operating temperature of AI-0.41AlNp reaches 375? and the short-term permissible operating temperature reaches 425 ?,and both the alloys of Al-0.82AlNp and AI-1.64AINp can be operated stably for a long period of time at 425 ?.The excellent heat resistance of the alloy is due to the strong high-temperature thermal stability of AINp,for which phase transformation or growth during heating are not likely occur and the recovery and recrystallization of the alloy can be inhibited effectively.The heat resistance temperatures of the three alloys are much higher than that of existing heat-resistant aluminum alloy wires and the electrical conductivity of the alloys all exceeds 58%IACS,meeting the requirements of heat-resistant aluminum alloy wires.The alloys' comprehensive performance exceeds the national performance requirements of the heat-resistant aluminum alloy wires.(3)Research on The Influence of the Added AlNp on the Mechanical Properties,Electrical Conductivity and Heat Resistance Quality of 1070 Aluminum AlloyWhen preparing a small amount of AINp-reinforced aluminum alloy materials by casting process,AlNp is introduced into 1070 electric alloy in the form of Al-B-N crystal seed alloy,then it is found that both the tensile strength and electrical conductivity of the alloy are improved.When 2%of crystal seed alloy is added,the tensile strength and electrical conductivity of 1070 aluminum alloy is 85MPa and 62.12%IACS respectively,which is 28.8%and 3.2%higher than that when the master alloy is not added,and the alloy elongation decreases from 48.5%to 35.8%.The increase of the strength of the alloy is due to the strengthening of the second phase of nano AlNp.At the same time,the AlB2 phase reacts with the trace transition metallic elements(such as Ti,V,Zr,Cr,etc.)in the melt to purify the melt and reduce the resistance,so the electrical conductivity of the alloy is also improved.After testing the heat resistance quality of the extrusion bar before and after adding 2%of Al-B-N crystal seed alloy,it is found that the short-term permissible operating temperature of the 1070 aluminum alloy increases from the original temperature of 150? to 210?.This is mainly because that the pinning effect of the nano AINp on dislocations hinders the movement of dislocations,and thus increases the recrystallization temperature of the alloy.The addition of the master alloy not only solves the problem that electrical conductivity and heat resistance of the heat-resistant conductive aluminum alloy can not exist simultaneously,but also is efficient and environmentally friendly,so it is recommended that the method be used in the industrial production of conductive aluminum. |
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