Effect Of Fire On Microstructures And Properties Of Copper And Its Welded Joint

With the rapid development of society and economy, fire has become one of the world's great pernicious disasters in permanent disasters . Related statistics show that in recent years, what caused the major electrical fire is the wire or cable, and its materials are mainly copper. Current identification of fire is mostly by identifying the molted mark of copper to obtain information about fire. We often overlooked electrical injury caused by the fire flames and radiant heat on the wires and joints. In the light of severe electrical fire situation, we must investigate the cause of the fire, and make evaluation on the recycle of these non-melted wire and cable and welded joints, which in order to avoid secondary hazards caused by material failure.The subject used TIG and select the appropriate processing parameters on the copper plate welding, and simulated the effect on 2.5mm² copper wire as well as T3 copper welded joints with the thickness of 3mm, 4mm and 6mm at different temperatures and cooling methods, Through microstructure, composition, as well as mechanical and electronic properties of the copper wire and its welded joint, the effect of microstructures and properties of temperature on copper welded joints were investigated. The electrical properties on temperature have been discussion intentionally. And with the theory of metal crystallization and heat treatment, the paper also makes theoretical analysis preliminary discussion on the mechanism of fire on metals and changes of physical properties. Following are the main results:(1) When the fire temperature is low, the mechanical properties of the copper and its welded joints will be slightly higher or declining slowly due to annealing enhanced; When the temperature is higher than 650 700℃, the mechanical properties significantly decreased, which causes the seriousness damage;(2) Electrical resistivity has little changes, but fall down totally. When the temperature is higher than 650 700℃, the decline increases. (3) When copper wire is at temperatures below its melting point in fire ,the main changes occur within the crystal structure and surface oxidation, its microstructure wasα-Cu equiaxed grain and accompanied by partial annealing twins. The major impact of temperature on the performance is the degree of changes in the grain. When it after welding, the microstructures of welded joint is coarse grains ofα-Cu, separate out (Cu + Cu₂O) eutectic at grain boundary, and crystal within the celluliform metastructure generated. The properties changes are caused mainly by the growth of the substructure as well as the number and distribution of O elements.