Suppression of spiking defects in deep penetration electron beam welded ETP copper

Abstract

AbstractThe electron beam is an appropriate tool to weld pure copper due to its high absorptivity on the copper surface, a high power density and inert vacuum environment. However, deep penetration electron beam welding of pure copper often produces the spiking defect. In this work bead on plate electron beam welding was done on Cu-ETP. A critical welding speed was determined for the distinction between a conduction-determined (at lower welding speed) and a non-conduction-determined welding speed range (at higher welding speed). The influence of high preheating temperatures was shown. The welds were investigated by light optical microscopy, electron backscatter diffraction measurements, ultrasonic testing, in situ thermal imaging, electrical resistance measurements and tensile tests. It was shown that in the conduction-determined welding speed regime without preheating, full and partial penetration welds exhibited root porosity. This effect was related to the overheating of the weld pool in combination with the phenomena causing spiking. Low defect root formation was achieved by using welding speeds greater than the critical value or by applying high preheating temperatures. The joints reached up to 98% of the international annealed copper standard in terms of specific electrical conductivity. Rupture took place within the joints during tensile tests. The joints exhibited up to 77% of the ultimate tensile strength of the base metal. Welds carried out with preheating exceeded the base metal regarding the fracture strain.