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The new all-aluminum alloy conductors gradually replace the steel core conductors and develop rapidly and are widely used around the world in aerospace, construction, automobile, and civil industries. The main production of aluminum alloy conductors is elaborated, pure aluminum series, Al–Mg–Si series, Al–Fe series, and Al–Zr–RE (rare earth) series. Some traditional processing methods and novel materials forming technologies are necessary processes for aluminum alloy conductors to improve their mechanical properties and conductivity, such as alloying elements additions, severe deformation, heat treatments, selective laser melting, and Al-based composites. Clarifying the relationship between different series aluminum alloy conductors’ morphologies and related properties is helpful to solve the bottleneck problems of key common technologies in the power transmission industry such as material research, structure design, and production technology. Graphical abstract

In this study, the Nb from the lightweight Ti65(AlCrNbV)35 medium-entropy alloy was replaced with Zr to create lower-density Tix(AlCrZrV)100−x (x = 65, 67, 70, or 75) alloys. All alloy ingots were fabricated through vacuum arc melting and drop casting. X-ray diffraction analysis revealed all as-cast alloys exhibited only a single body-centered cubic structure. As the Ti content increased, the strength of the as-cast alloys decreased from 1247 to 981 MPa, whereas their elongation marginally improved. Moreover, the mechanical properties of these alloys were considerably enhanced through thermomechanical treatment (50% hot rolling and 80% cold rolling) and then rapid annealing at 700 °C, 800 °C, or 900 °C. An increase in the annealing temperature led to a notable decrease in the yield strength of the alloys but a considerable increase in their ductility. Ti65, Ti67, and Ti70 alloys annealed at 700 °C or 800 °C exhibited a yield strength of ≥1200 MPa and a ductility of ≥10%. Of the fabricated alloys, the Ti67 alloy annealed at 700 °C exhibited the optimal mechanical properties (yield strength of 1552 MPa and ductility of 13.6%). It exhibited low density (4.89 g/cm3) and a specific yield strength of 317 MPa·cm3/g, thus demonstrating considerable potential for transportation and energy applications.

Conference COMAT deals with recent trends in structural materials that cover production technologies (casting, forging, rolling, additive manufacturing...), heat and thermo-mechanical treatments, computer modelling and physical simulations and materials characterisation. COMAT started in 2010. Therefore, we celebrated already 12th anniversary of the conference the last year. The event was organized by traditional tandem COMTES FHT Inc. and TANGER Ltd. We had high expectations for this meeting after two years of COVID restrictions. Unfortunately, many of them remained valid till the conference took place and we had very narrow range of foreigner participants and rather low number of participants in comparison with the previous years. Lower number of participants lead to single session conference, which in turn resulted in very friendly and constrictive atmosphere, when all sessions had much more audience and discussions, than it was in the previous years, when parallel sessions systems was implemented. For COMAT 2022 we agreed for the first time on selected paper publication in Materials journal, leading to smaller amount of papers to be found in these proceedings, but we still hope the readers will find these proceedings interesting and inspiring. These articles were reviewed by 20 experts.We are looking forward to seeing you all personally at COMAT 2024.

The present study involves the fabrication of aluminium alloy 6061 matrix hybrid composites with varying weight fractions of silica sand and copper particles by employing the conventional stir casting method. The combined influence of age hardening (AH) and low temperature thermomechanical treatment (LTMT) on the hardness and tensile properties of AA6061 hybrid composites was investigated. The uniform dispersion of the particles in the matrix was confirmed by microstructure analysis and the improvement of Brinell hardness values. The composites exhibited higher tensile strength and hardness than the base alloy. Both AH and LTMT enhanced the properties of the hybrid composites and a comparison between them revealed the best results for LTMT hybrid composites. The LTMT hybrid composite with 3 wt% silica sand and 3 wt% copper (3S3C) subjected to 12% rolling deformation and aged at 100 °C had the highest hardness and tensile strength of 144.26 HV and 290 MPa respectively. The hardness and tensile strength of AA6061-3S3C hybrid composite subjected to LTMT in peak aged condition showed an improvement of 125 and 97% respectively when compared with those of AA6061 alloy. Fracture surface analysis of the thermomechanical treated composites in peak aged condition showed a mixed mode of failure dominant with the ductile fracture.

The effect of high-temperature thermomechanical treatment (HTMT) with plastic deformation by rolling in austenitic region on the microstructure and mechanical properties of 12% chromium ferritic-martensitic steel EP-823 is investigated. The features of the grain and defect microstructure of steel are studied by Scanning Electron Microscopy with Electron Back-Scatter Diffraction (SEM EBSD) and Transmission Electron Microscopy (TEM). It is shown that HTMT leads to the formation of pancake structure with grains extended in the rolling direction and flattened in the rolling plane. The average sizes of martensitic packets and ferrite grains are approximately 1.5–2 times smaller compared to the corresponding values after traditional heat treatment (THT, which consists of normalization and tempering). The maximum grain size in the section parallel to the rolling plane increases up to more than 80 µm. HTMT leads to the formation of new sub-boundaries and a higher dislocation density. The fraction of low-angle misorientation boundaries reaches up to ≈68%, which exceeds the corresponding value after HTMT (55%). HTMT does not practically affect the carbide subsystem of steel. The mechanical properties are investigated by tensile tests in the temperature range 20–700 °C. It is shown that the values of the yield strength in this temperature range after HTMT increase relative to the corresponding values after THT. As a result of HTMT, the elongation decreases. A significant decrease is observed in the area of dynamic strain aging (DSA). The mechanisms of plastic deformation and strengthening of ferritic-martensitic steel under the high-temperature thermomechanical treatments are also discussed.

Simultaneously achieving high strength and ductility has been a long-standing goal in aluminum alloys, while the increase in strength usually leads to ductility loss. In this study, a novel thermomechanical treatment (TMT) method, i.e., pre-existing precipitation in coarse grain (CG) and cryogenic rolling plus warm rolling followed by peak aging, is developed to achieve high strength and good ductility in 211ZX aluminum alloy. As a result, a composite nanostructure including ultrafine-grained (UFG) and nanoprecipitation is obtained. Compared to a conventional T6 sample, the multi-step TMT sample has a finer grain (205 nm), while numerous GP zones and θ\" phases are dispersed inside the grain. The precipitation characteristics are similar to the T6 sample. The yield strength (635 MPa) and ultimate tensile strength (690 MPa) are about 81% and 53% higher than the T6 sample, respectively, with only a slight decrease in plasticity. Microstructural characterization and thermodynamic analysis confirmed that pre-existing precipitates and cryogenic temperatures facilitate the formation of the composite nanostructure. Quantitatively strengthening calculations demonstrate that the high strength is attributed to the ultra-fine grain strengthening and precipitation strengthening, while the high plasticity is mainly due to the reduction of dislocation density caused by recovery and recrystallization during the aging process as well as the massive production of nano-GIPs (interior grain precipitates).

Thermomechanical processing of cast structures is an effective solid working route of generating thixotropic morphologies after subsequent partial melting and is in use for decades to manufacture the bulk billet feedstock for thixoforming from a variety of alloys. The solid-state deformation is also critical for coarse particulate feedstock, utilized for semisolid forming either directly or after compaction into billets. Although the original concept, called strain-induced melt activation (SIMA), defined the specific procedure, the term became generally recognized synonym for a variety of thermomechanical treatments offering an opportunity of controlling the solidification microstructure. This review covers transformations during solid-state deformation, reheating to semisolid state and isothermal holding within solidus–liquidus range, and solidification of thixotropic slurries. Essentials of semisolid metal processing, necessary to understand the subject, are supported by details related to specific implementation techniques and alloys. Application examples at laboratory and commercial levels and properties achieved with conventional and severe plastic deformation techniques, for different alloys along with present limitations, are described. The link between solid-state deformation-enhanced melting and liquid metal engineering is emphasized throughout the paper in terms of the common goal of controlling the solidification outcome in order to develop technology for mass-scale production of net-shape components having performance characteristics superior to conventional castings.

The COMAT conference addresses recent trends in structural materials, encompassing production technologies (casting, forging, rolling, additive manufacturing, etc.), heat and thermo-mechanical treatments, computer modeling and physical simulations, and materials characterization. Since its inception in 2010, COMAT has become a recognized event in the field. This year, in September 2024, we celebrated the 8. anniversary of the conference in Pilsen. The event was once again organized by the established partnership of COMTES FHT Inc. and TANGER Ltd. Following the challenges of recent years, we were delighted to welcome approximately 80 participants from 9 countries to Pilsen, with over 30% of attendees representing international institutions. The COMAT 2024 Conference Committee was attended by Prof. Peter Anderson from The Ohio State University, Dr. Norman Herzig from Nordmetall GmbH and Prof. Carolin Körner from Friedrich-Alexander Universität. Building on the positive experience of the single-session format from previous years, COMAT 2024 continued this approach. This structure proved highly effective, fostering a very engaging and productive atmosphere. The single sessions ensured strong attendance at all presentations, leading to lively discussions and enhanced opportunities for networking among participants and our partners. A dedicated poster session further enriched the conference program, showcasing the latest research and innovations in structural materials. The poster awards were announced during our traditional conference dinner at the Pilsner Urquell brewery, providing a fitting culmination to the event. These proceedings capture a selection of the presentations and discussions from COMAT 2024. While the selection process for these proceedings was rigorous, we believe the included papers offer valuable insights and inspiration to the wider materials science community. We are confident that readers will find these contributions both interesting and informative.We are looking forward to seeing you all personally at COMAT 2026.Yours faithfullyJan DŽUGANConference chairman and Proceedings editorMarch 2025

The effect of high-temperature thermomechanical treatment on the structural transformations and mechanical properties of metastable austenitic steel of the AISI 321 type is investigated. The features of the grain and defect microstructure of steel were studied by scanning electron microscopy with electron back-scatter diffraction (SEM EBSD) and transmission electron microscopy (TEM). It is shown that in the initial state after solution treatment the average grain size is 18 μm. A high (≈50%) fraction of twin boundaries (annealing twins) was found. In the course of hot (with heating up to 1100 °C) plastic deformation by rolling to moderate strain (e = 1.6, where e is true strain) the grain structure undergoes fragmentation, which gives rise to grain refining (the average grain size is 8 μm). Partial recovery and recrystallization also occur. The fraction of low-angle misorientation boundaries increases up to ≈46%, and that of twin boundaries decreases to ≈25%, compared to the initial state. The yield strength after this treatment reaches up to 477 MPa with elongation-to-failure of 26%. The combination of plastic deformation with heating up to 1100 °C (e = 0.8) and subsequent deformation with heating up to 600 °C (e = 0.7) reduces the average grain size to 1.4 μm and forms submicrocrystalline fragments. The fraction of low-angle misorientation boundaries is ≈60%, and that of twin boundaries is ≈3%. The structural states formed after this treatment provide an increase in the strength properties of steel (yield strength reaches up to 677 MPa) with ductility values of 12%. The mechanisms of plastic deformation and strengthening of metastable austenitic steel under the above high-temperature thermomechanical treatments are discussed.

The deformation microstructures formed by novel multistage high-temperature thermomechanical treatment (HTMT) and their effect on the mechanical properties of austenitic reactor steel are investigated. It is shown that HTMT with plastic deformation at the temperature decreasing in each stage (1100, 900, and 600 °C with a total strain degree of e = 2) is an effective method for refining the grain structure and increasing the strength of the reactor steel. The structural features of grains, grain boundaries and defective substructure of the steel are studied in two sections (in planes perpendicular to the transverse direction and perpendicular to the normal direction) by Scanning Electron Microscopy with Electron Back-Scatter Diffraction (SEM EBSD) and Transmission Electron Microscopy (TEM). After the multistage HTMT, a fragmented structure is formed with grains elongated along the rolling direction and flattened in the rolling plane. The average grain size decreases from 19.3 µm (for the state after solution treatment) to 1.8 µm. A high density of low-angle boundaries (up to ≈ 80%) is found inside deformed grains. An additional cold deformation (e = 0.3) after the multistage HTMT promotes mechanical twinning within fragmented grains and subgrains. The resulting structural states provide high strength properties of steel: the yield strength increases up to 910 MPa (at 20 °C) and up to 580 MPa (at 650 °C), which is 4.6 and 6.1 times higher than that in the state after solution treatment (ST), respectively. The formation of deformed substructure and the influence of dynamic strain aging at an elevated tensile temperature on the mechanical properties of the steel are discussed. Based on the results obtained, the multistage HTMT used in this study can be applied for increasing the strength of austenitic steels.