Study On The Microstructure And The Mechanical And Electrical Properties Of Copper Alloy Wires Prepared By Continuous Directional Solidification Process

On the basis of the profound analysis of the strengthening and electrical conductive mechanism of high strength high electrical conductivity copper alloys and considering there is no cross boundary between column crystal or cellular crystal grains, electrical conductive property of copper alloy can be achieved at maximum. Continuous directional solidification process was used in this thesis to greatly improve the strength and hardness and meanwhile keeping quite higher electrical conductivity of certain selected copper alloy system, especially higher temperature mechanical property, anti-creep capability of copper-silver and copper-chrome alloys have been dramatically enhanced.In this paper, the preparation and forming processes of copper-silver and copper-chrome alloys wires are introduced and analyzed in detail. By means of scanning electronic microscope (SEM) and optical microscope (OM) technique, the microstructures in the states of casting, cold working and heat treatment are observed. The conformational character and forming mechanism of microstructures are analyzed. Meanwhile the mechanical and electrical properties in various states of the copper-silver alloy are discussed. The microstructure evolvement of copper alloys is studied by X-Ray diffraction (XRD) .Finally; the thermal stability of copper alloy has been analyzed in detailed with Differential Thermal Analyzer (DTA).The experimental results show that the microstructure evolvement varies with the casting speed. The single crystal can be obtained at the lower casting speed; otherwise column crystal along with the casting direction can be obtained. The room temperature mechanical property of copper-silver alloy wire corresponds to single crystal copper, while tensile strength can be achieved to 400Mpa from 150 MPa of as-casting when deformation rate is about 75%. The higher temperature mechanical property of copper-silver alloy wire overmatches the single crystal. Copper-silver alloy wire, which deformation rate is about 75%, its tensile strength ratio between no-soften and after intenerating anneal outgoes 96%, while single crystal copper wire's tensile strength ratio is no more than 60% even though deformation rate is same. The tensile strength and hardness of copper-silver alloy wire, which deformation rate is about 75%, can be achieved maximum after eliminating stress anneal at 250 Celsius degree. The recrystalization origination temperatures of single crystal, copper-silver alloy and copper-chrome alloy are 268,358 and 426 Celsius degree respectively.The as-casting copper-silver alloy rod has a lower electricity resistance. The electricity resistance rate can be slightly increased after drawing and can be partly resumed after being annealed. The resume of the electricity resistance are related with the time and temperature of heat treatment The electrical conductive rate of copper-silver alloy is no less than 98%IACS (International Annealed Copper Standard).Copper-silver and copper-chrome alloys wires manufactured by continuous directional solidification process have excellent synthetics properties and the thermal stability, which is extreme important to copper alloys used for higher temperature. The strength and hardness of copper alloys can be enhanced to great limitation by using continuous directional solidification process and meanwhile maintaining quite higher electrical conductivity. It is suggested that continuous directional solidification process should be an advanced technique in manufacturing high-strength and high-electrical conductivity copper alloy and possess great application prospects.