Obtaining Hollow Semifinished Products Based on Copper Alloys for Electrical Purposes by Means of Screw Rolling

A process for obtaining semifinished products in the form of pipes made of copper alloys for electrical purposes by means of screw rolling is proposed. The results of experimental piercing and rolling of tube samples made of Cu-0.75Cr alloy billets with a diameter of 45 mm are presented. The samples, 43.5 x 10.0 mm in size, obtained after piercing with the use of a two-roll screw rolling mill, have exact geometrical dimensions: the deviation of the outer diameter at the front end is less than 1%, that at the rear end is less 2.4%, the relative nonuniformity of pipe wall thickness at the front end amounts to 0.3-0.5%, and that at the rear ranges within 0.5-1.0%. The pierced pipe samples have been rolled by using a three-roll minimill for radial-shear rolling (RSR) with a different total reduction level; the samples have been obtained with an outer diameter of 30, 25, and 18 mm. The reduction process has been analyzed from the standpoint of stability and deformation of the mouth of pipe. In the case of a 30% relative reduction of the outer diameter, the rolling without a mandrel is accompanied by an increase in the wall thickness. The deviations of the inner diameter are within permissible limits. The experiments performed for obtaining samples based on the Cu-0.75Cr alloy by means of screw piercing and reduction using an RSR mill show that this technique could be implemented in industry. At the same time, in order to obtain a quality product, it is necessary to more exactly determine the deformation parameters (deformation level and reduction mode). Different variants for the heat treatment (HT) of the pipe samples and the effect of the HT mode exerted on the electrical conductivity and hardness are considered. After piercing, the samples exhibited a conductivity of 59.3% IACS. The maximum electrical conductivity of 76.7% IACS has been obtained for the samples after quenching from a temperature of 1020 degrees C and aging at 450 degrees C for 3 h. The results of this work show that it is fundamentally possible to obtain semifinished products based on copper alloys for electrical purposes by means of screw rolling.