Fatigue failure of overhead line conductors made of AlMgSi alloys is much more complex than fatigue failure of a single wire. The main difference lies in the fretting phenomenon, which is a significant mechanism initiating fatigue damage. It is generated because of micro-movements between individual wires or outer wires and overhead line fittings. Such movements are mainly caused by aeolian vibrations, which lead to degradation of wire surface, initiation of microcracks, and premature failure of multiple wires. Research based on laboratory experiments and modeling studies simulating real operating conditions made it possible not only to identify the mechanisms leading to failure but also to assess the impact of working conditions on their evolution. According to the obtained results, properly selected heat treatment parameters influence both the mass decrease of the wires and number of cycles to failure due to fretting fatigue. Further development of materials, protective coatings, and methods of durability prediction will reduce the impact of fretting on fatigue failure and thus increase the reliability of power lines.

This study presents the results of research on the influence of different contents of copper in aluminium alloys based on the 6xxx series on mechanical and structural properties. The investigation started with the alloying, and casting four billet variants with different copper content—0.8% Cu; 2B—1% Cu; 3A—1.2% Cu; and 3B—1.4% Cu. The prepared materials were homogenised and extruded on a 500T horizontal press with two different process temperatures and ram speeds ranging from 1 mm/s to 9 mm/s. After heat treating to the T6 and T5 tempers, their mechanical properties were tested. On this basis, the two most promising alloys 2A and 3B were selected and subjected to further tests. After extrusion and heat treatment of the profiles (to F, T1, T2, T5, and T5510), their mechanical properties were determined to select the preferred process parameters. Finally, a structural test based on crystallographic orientation based on the EBSD technique and TEM observations allowed for the characterisation of grain size, dispersoids, and phase analysis. Bright-field (BF) analysis allowed us to compare the deformed areas for T1, T5, and T5510 temperatures. The results showed significant growth in the mechanical properties of all the subjected alloys, and the best properties were shown for a Cu content of 1.4% with a tensile strength of 460 MPa and an elongation of 16% (T5510 tempering). The structural test showed an average grain size of 18 µm to 23 µm and solid solution decomposition differences for different heat-treating parameters.

In the first part of the work, the 3-step homogenization procedure was carried out for AlMgSi(Cu) alloy, aimed at obtaining billets microstructure with numerous fine particles of strengthening phases and increased solidus temperature. In the second part of the work, an original on a global scale prototype device for the dynamic stretching of extruded profiles before artificial ageing, was proposed and tested in semi-industrial conditions. The thermo-mechanical treatment of extruded hollow profiles from AlMgSi(Cu) alloy with 1.22% content of copper was performed with dynamic deformation range: 0.25%, 0.5%, 1%, 1.5% and 2%. The microstructural inspection was performed in the welding area and outside the weld for variant after only extrusion and for variant after extrusion and dynamic stretching before artificial ageing. It was revealed that the designed three-stage homogenization treatment led to dissolution of soluble phases present in the as-cast billets microstructure, which caused significant increase in solidus temperature, from 509 °C in as-cast state to 573 °C after completed soaking. The application of dynamic deformation during the straightening of aluminium profiles after hot extrusion with water cooling on the press run, led to the induced favourable changes in the microstructure of the alloy, which translated into a significant increase in UTS of about 11%.

FEM numerical analyses can be indicated as a common and basic tool used in the design of processes based on the plastic forming of metals. In such simulations, the accuracy of the results strongly depends on the quality of the material constitutive data used as the input. Good understanding of metals and their alloys’ deformation behavior, especially at hot working temperatures, is the key to developing or optimizing proper and economical processes. To provide reliable FEM simulation results, it is crucial to select an appropriate experimental method describing material behavior at elevated deformation temperatures. The most commonly method used for this is hot torsion tests, which can effectively provide a basis for developing constitutive models (for example, the Hensel–Spittel equation), but also produce the material constants needed to fully describe the behavior of the metal. This paper analyzes three experimental methods, compression testing, torsion testing, and spherical probe pressing, for determining material flow stress characteristics required for FEM simulations. The study focuses on the EN AW-7075 alloy, a high-strength aluminum alloy with limited hot workability. The methods were validated by comparing FEM predictions of extrusion force and profile temperature with results from industrial extrusion trials conducted on a 5 MN horizontal press.

This paper outlines preliminary findings from studies on the possibility of using hot torsion testing for the physical modeling of microstructural evolution during aluminum alloy extrusion processes. Accordingly, two plastic deformation processes were investigated: high-temperature torsion and extrusion. The studies were conducted within the temperature range characteristic of the extrusion of 16 mm diameter round profiles made of EN AW-6060 aluminum alloy, with different cooling rates after deformation. Physical modeling of both processes was preceded by numerical modeling with the finite element method (FEM) and a detailed analysis of the deformation conditions occurring during both processes. Thanks to the careful selection of thermoplastic forming parameters, comparable values of the strain, strain rate, and temperature of profiles suitable for direct microstructural comparison were obtained. The conducted studies made it possible to determine the influence of the applied thermoplastic forming parameters on the microstructural evolution of the tested material. Finite element method simulations revealed distinct strain gradients in both the hot torsion and extrusion processes. Metallographic analysis of the EN AW-6060 alloy showed a strong dependence of grain size and the degree of recrystallization on the thermoplastic processing temperature and the local strain level. The obtained results confirm that hot torsion testing, combined with the selection of representative regions based on FEM analysis, can serve as a supporting method for modeling microstructural evolution in industrial extrusion processes, provided that the thermomechanical conditions correspond to those occurring in the modeled process.