Characterization of joining copper rods by upset technique and investigating the effect of preheat treatment on the weld characteristics

Abstract

Abstract The present work studies the rod-rupture problem that occurs in the Copper and Mechanical State Company during the upcast production of 8 mm copper rods. This rod-breaking problem arises at the time of rolling the upcasted coils due to reasons of electricity fluctuations, impurities in the metal, etc. Upset welding, as a non-melting joining, was chosen and investigated to weld the copper rods to produce coils with the predetermined length for commercial applications. The welding solution was applied to avoid the negative effects of returning the cut drawn length back to the start of the production line to draw the predetermined length of the coil as one unit, which consumes extensive time and cost. The welding was performed by altering the applied welding current in three modes to investigate the effect of changing the heat input on the properties of the joints. Alternatively, the impact of preheat treatment of the welded joints on the various studied properties was also studied. The joint quality of the resultant welded rods has been characterized by studying their mechanical properties (in terms of tensile stress and elongation%), electrical conductivity (by more than one measuring method), metallographic examination, as well as morphological characterization. The results revealed that the tensile stress, average elongation%, as well as electrical conductivity related to the welded rods, were acceptable concerning the unwelded base metal, even in the case of a higher input heat. Moreover, a smooth and crack-free microscopic structure of the welded drawn wires was obtained, despite the nonperformance of preheat treatment, revealing that the heat treatment has no notable impact on the studied properties.