Search Results (7)

Direct fusion welding of aluminum (Al) to magnesium (Mg) results in the formation of brittle intermetallic compounds (IMCs) that significantly restrict the application of these joints in structural applications. In this study, cold spray, a promising solid-state coating deposition technology, was employed to introduce a nickel (Ni) interlayer to facilitate joining of Al to Mg sheets by means of resistance spot welding (RSW). The ability of cold spraying to deposit metallic powder on the substrate without melting proves beneficial in mitigating the formation of the Al-Mg IMCs. The Ni-coated coupons were subsequently welded via resistance spot welding at optimized parameters: 27 kA for 15 cycles in two pulses with a 5-cycle inter-pulse delay. Scanning electron microscopy confirmed metallurgical bonding between the Al, Mg, and Ni coatings in the fusion zone. It is shown that the bonding between the three elements inhibits the formation of deleterious IMCs. Tensile shear testing showed joint strength exceeding 4.2 kN, highlighting the potential of the proposed cold spray RSW approach for dissimilar joining in structural applications. Full article

The present study focuses on investigating the evolution of phase transformations in the Mg-Ni-Ce system under the influence of mechanical synthesis (MS) and spark plasma sintering (SPS). Magnesium powder mixtures with different nickel and cerium contents (Mg-3%Ni-2%Ce, Mg-7%Ni-3%Ce, and Mg-10%Ni-5%Ce) were mechanically activated along with various grinding parameters. The X-ray phase analysis (XRD) has shown the successive stages of the phase formation in the MS process: from the initial components to the formation of intermetallic compounds of Mg₂Ni, Mg₁₂Ni₆, and CeMg₃. An increase in the intensity of mechanical treatment facilitated the accelerated destruction of the crystal lattice, the generation of defects, and the formation of new phases, as evidenced by the broadening and reduction in the intensity of Mg diffraction peaks. The subsequent SPS stage promoted the completion of phase transformations, structural stabilization, and the formation of a dense, multicomponent microstructure with a uniform distribution of intermetallic compounds. The observed average crystallite sizes ranged from 20 to 70 nm, depending on the processing conditions. The research results demonstrate the possibility of targeted control over the phase composition, opening new opportunities for the development of highly efficient hydrogen-absorbing alloys. Full article

Given by their low weight and favorable combination of properties, Al-Fe-Si-based intermetallic and duplex alloys are widely used in mechanical engineering. The use of aluminum scrap for their production imparts the necessity for a thorough study of the impacts of presence of impurity/alloying elements on the phase composition. By this reason, individual impacts of the impurity/alloying elements present in the majority of commercial alloys on phase compositions of the alloys were studied herein. Particular emphasis was on the formation of the α phase and features of the α↔β transformation, as well as on their effects on the solidus, liquidus, and phase transformation temperatures. Modeling was used to study the synergistic effect of the simultaneous introduction of 12 elements into aluminum. According to the results, magnesium, copper, and nickel have a tendency to form combined intermetallic phases, and beryllium, as a structurally free element, forms precipitates even at minimum concentrations. Verification of the modelled results was performed using a real alloy prepared experimentally from commercially available raw materials. The comparison of the results provided by computer modeling and the actual phase composition showed sufficient agreement. The herein acquired results contribute to a deeper understanding of the features of phase transitions occurring during alloying of aluminum alloys and will also be useful for predicting microstructures and phase compositions of intermetallic alloys. This research has potential to inspire further development in materials science and engineering. Full article

Crystallization includes liquid/solid and solid/solid phase transitions, important processes for improving engineering material performance, which have attracted significant attention in the community. The current Special Issue (SI) entitled ‘Crystallization of High-Performance Metallic Materials’ has collected twelve research papers focusing on different aspects of the crystallization of metallic materials, e.g., the solidification of steel, fatigue and fracture behaviors of magnesium composites, nucleation of intermetallic compounds in aluminum alloys, microstructure evolution in nickel-based super-alloys, etc. The summary of crystallization behaviors at different temperature ranges in different metallic materials contributes to the state of the art of engineering material development. Full article

Mg₂Ni is a highly promising candidate for solid-state hydrogen storage due to its high storage capacity. However, its synthesis is challenging due to the high melting point of Ni (1455 °C) and the boiling point of Mg (1090 °C). In this study, elemental powder mixtures of Mg and 30 at% Ni were processed by high-pressure torsion (HPT) to synthesize the Mg₂Ni intermetallic compound through mechanical methods. The formation of 11 wt% of Mg₂Ni after 50 turns of HPT was confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS), reaching a maximum of 59 wt% after 100 turns. Rietveld refinement confirmed a nanocrystalline size for the Mg₂Ni phase synthesized via HPT. Hydrogenation tests showed that the Mg-Ni synthesized by HPT can absorb hydrogen at 350 °C even after several weeks of air exposure. Furthermore, a maximum absorption capacity of 3.8 wt% was reached after 20 h of hydrogen exposure for the sample with 100 turns. This capacity is close to the theoretical capacity of 3.9 wt% for this composition. The results confirm that combining HPT with subsequent heat treatment is an efficient strategy to increase the Mg₂Ni fraction after HPT processing. Full article

Wire arc additive manufacturing is currently rising as the main focus of research groups around the world. This is directly visible in the huge number of new papers published in recent years concerning a lot of different topics. This review is intended to give a proper summary of the international state of research in the area of wire arc additive manufacturing. The addressed topics in this review include but are not limited to materials (e.g., steels, aluminum, copper and titanium), the processes and methods of WAAM, process surveillance and the path planning and modeling of WAAM. The consolidation of the findings of various authors into a unified picture is a core aspect of this review. Furthermore, it intends to identify areas in which work is missing and how different topics can be synergetically combined. A critical evaluation of the presented research with a focus on commonly known mechanisms in welding research and without a focus on additive manufacturing will complete the review. Full article

The low density and good mechanical properties make magnesium and its alloys attractive construction materials in the electronics, automotive, and aerospace industry, together with application in medicine due to their biocompatibility. Magnesium AZ91D alloy is an alloy with a high content of aluminum, whose mechanical properties overshadow the low corrosion resistance caused by the composition of the alloy and the existence of two phases: α magnesium matrix and β magnesium aluminum intermetallic compound. To improve the corrosion resistance, it is necessary to find an effective protection method for the alloy surface. Knowing and predicting electrochemical processes is an essential for the design and optimization of protective coatings on magnesium and its alloys. In this work, the formations of nickel protective coatings on the magnesium AZ91D alloy surface by electrodeposition and chemical deposition, are presented. For this purpose, environmentally friendly electrolytes were used. The corrosion resistance of the protected alloy was determined in chloride medium using appropriate electrochemical techniques. Characterization of the surface was performed with highly sophisticated surface-analytical methods. Full article