Abstract
The article focuses on the Direct Drive Rotary Friction Welding of ultrafine-grained copper rods, which feature increased mechanical properties and good electrical properties, yet are limited in size. The use of UFG metals is often limited by the too small dimensions of semi-finished elements produced by SPD methods. Therefore, the production of finished machine parts from UFG metals is currently economically unjustified. Dismissal of dimensional limitations can be done by introducing joining to technological processes. The proposed joining method does not lead to a melting of the material in the joining zone or excessive degradation of the UFG microstructure. To obtain the best results, the research used the method of low-energy welding of two kinds of specimens: with a flat or a conical contact surface. In the article, the authors present, by means of metallographic microsections and microhardness measurements, the influence of rotational speed, welding pressure and conical shape contact surface on the quality of the obtained joints. The conducted research made it possible to obtain good quality joints whose microhardness is reduced only by about 10% in comparison with the base material and the tensile strength dropped from only 397–358 MPa.
Highlights
In recent years, there has been significant interest in the manufacturing of ultrafine-grained (UFG) metals, i.e., those with an average grain size of less than 1 μm
Despite using a wide range of parameters, none of the attempts was fully successful, as it was not possible to produce a joint without discontinuities in the weld, as reflected by the low joint coverage degree (JCD) values of 70%, 39% and 50% for the R106, R501 and R502 samples, respectively, and by the total coverage degree (TCD) values (44%, 31% and 45%)
The lowest decrease in microhardness obtained in the present study, as well as in those cited, was about 10%. These results indicate that DD-Rotary Friction Welding (RFW) is an attractive method for joining rods, since it makes it possible to obtain results similar to those from Friction Stir Welding (FSW), currently considered to be one of the most promising methods
Summary
There has been significant interest in the manufacturing of ultrafine-grained (UFG) metals, i.e., those with an average grain size of less than 1 μm. There are reports on joining UFG materials using friction welding [13], such as RFW for joining UFG aluminum alloys [14]. For these kinds of reports, tensile test and microhardness are usually carried out [15]. Other published reports on RFW tests were carried out on 316L UFG steel rods and showed quite a significant deterioration in mechanical properties, where the microhardness in the weld area dropped by 40% [16]. Other attempts at joining UFG copper were made using FSW [17], where significant grain growth and an associated decrease in hardness in the heat-affected zone were observed
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