Solid State Phenomena Vol. 353

Abstract: The influence of Sc on the mechanical properties and microstructure evolution an AA5083 was studied. AA5083/0.33wt%Sc was prepared by stir casting, and then this alloy was subjected to a cryorolling process at-196°C with 50 % rolling reduction. The mechanical properties of the specimens were measured by tensile strength testing and Vickers microhardness test. Furthermore, the microstructure of specimens was analyzed by X-Ray diffraction analysis, scanning electron microscopy (SEM), optical microscopy and electron back scattered diffraction. The ultimate tensile strength (UTS) of the base AA5083 alloy was 238 MPa, which increased to 244 MPa after adding 0.33wt%Sc. After subjecting the as-cast AA5083/0.33wt%Sc to 50% cryorolling reduction, the UTS increased to 404 MPa. The fractured surfaces revealed a large-scale dimpled structure, similar to the ductile fracture mechanism in the starting material. In the cryorolled sample, a fibrous morphology with tiny dimples was observed, corresponding to the low elongation.

Abstract: The manufacturing of internal thread using the helical thread forming process (Punch Tap) as a novel high-performance manufacturing technology provides high productivity by reducing the tool path, which can save manufacturing time up to 75% compared to the conventional thread forming process. For instance, cast gearboxes in the transport sector consisting of numerous internal threads can benefit from this manufacturing method to realize detachable joints. While the required core hole diameter for conventional (cut) tapping depends on the thread dimension, this diameter depends either on the material properties for the thread forming process. The proper core hole diameter according to material flow possibility enables forming of complete thread profiles, which can consequently enhance the mechanical properties of the thread. This study aims to analyze the effect of the core hole diameter on the quality of the formed threads in AlSi10MnMg cast profiles. M6 threads were formed into the pre-drilled core holes with two different diameters. CT-scan analysis indicated that reducing the core hole diameter decreases the inner volume of the formed internal thread, which is justified by better material flow and complete forming of the thread profiles. Adaptation of the manufacturing parameters according to the material properties enhanced the geometry of the formed thread profiles. This enhancement increased the tensile and fatigue strengths of the detachable joints by subjecting the four initially formed threads at the top of manufactured nuts to the static and cyclic loads.

Abstract: High-entropy alloys (HEAs) have led to breakthroughs in materials science due to their superior properties and the challenge of achieving the high strength and high ductility trade-off. Microstructural evolution during cold and warm compression tests of the single-phase Al₈Cr₁₂Mn₂₅Fe₃₅Ni₂₀ high entropy alloy (Fe-HEA) is investigated in the present work. The current study assesses the effect of temperature on the mechanical properties and deformation mechanism of the face-centered cubic structure Fe-HEA. The arc-melted ingot is homogenized at 1473 K and then directly hot-rolled to break the cast structure of the alloy prior to testing procedures. Fe-HEA is tested through uniaxial compressive testing at three different selected temperatures: 293, 473, and 673 K utilizing a Gleeble thermo-mechanical simulator at a strain rate of 0.001 s^-1. The compressive behavior at 673 K showed a higher strain hardening exponent when compared to 293 and 473 K. The deformed microstructural features of the compressed and quenched specimens, deformation mechanism, and phase revolution are investigated with X-ray diffraction (XRD) and electron backscattered diffraction (EBSD). Dislocation densities for the deformed conditions were estimated to be 4.11 × 10¹⁴ and 5.39 × 10¹⁴ m^-2 for the 473 and 673 K deformed conditions, respectively. At a deformation temperature of 673 K, B2 precipitation is observed at the high-angle grain boundaries.

Abstract: In Cr-rich CoCrFeMnNi alloys, the precipitation of the σ phase at grain boundaries during recrystallization is so fast that ultrafine-grained structure is formed due to the pinning effect of the precipitates. The average grain size of the fcc parent phase is found to be consistent with modified Zener-Smith model. If conventional alloys come to equilibrium, volume fraction of precipitates should approach a saturation value. However, it is interesting to note that the volume fraction of the σ phase in Cr-rich CoCrFeMnNi alloys is inversely proportional to the average grain size of the fcc parent phase. For instance, in Co₂₀Cr₂₅Fe₂₀Ni₁₅Mn₂₀ alloys, the volume fraction changes from 6.5% to 1.2% with increasing average gran size from 14 μm to 210 μm even after annealing at 1273 K for 100 h. It is well known that heterogeneous nucleation of precipitates at grain boundary is energetically favorable and fast diffusion through grain boundary can assist the precipitation. However, they cannot account for the grain size dependence of the volume fraction after reaching equilibrium. Based on stereology, the reciprocal of grain size is proportional to grain boundary area. Thus, chemical fluctuation at grain boundaries (e.g. segregation) is considered to be related to the unusual precipitation at the grain boundaries.

Abstract: Open-cell type aluminum foam possesses unique structural characteristics comprising numerous interconnected pores within. This intriguing structure facilitates the passage of fluids (gas or liquid) through the interior of the open-cell type aluminum foams, enabling easy transfer to the exterior. The objective of this study is to manufacture open-cell type aluminum foams with varying pore sizes using the replication casting process and to evaluate their thermal properties. The equipment designed for the production of open-cell type aluminum foams consists of a chamber and an inner container. The chamber is connected to a vacuum line and an Ar gas line, with the container positioned inside. The aluminum alloys utilized for the foams were A356 and ADC12, and Na2CO3 served as the space holder. As a result of manufacturing the foams, there was no significant difference of porosity with space holder size and alloy types, the porosity averaged around 62%. To investigate the thermal properties of open-cell type aluminum foams in relation to pore size and alloy types, temperature variations were measured during sample heating via the hot plate method. Consequently, it was confirmed that the thermal properties of the foams were influenced by the structural conditions and alloy types.

Abstract: Aluminium alloy 6061 has a versatile application within industrial heat exchangers, heat sinks, chemical equipment, and frames of aircraft and ships. Its physical and mechanical properties such as lightweight, high strength, corrosion resistance, and thermal and electrical conductivity make it a suitable material choice for these applications. Within thermal and micro-electromechanical applications, such as heat exchanges, radiators, and heat sinks used in microelectronics, the dissipation of heat plays an important role. For optimum heat dissipation, a higher surface area is required. This can be achieved by modifying the surface by fabricating microchannels. A number of processing techniques are used for fabricating microchannels on different materials. A laser is a flexible non-contact machining tool that may be used to create any profile or contour on practically any material. In recent times due to the advancement in laser technology, the use of ultrafast laser material processing is one potential route toward further extending the fabrication of high-quality microchannels without defects caused due to heat-affected zones and in a sustainable manner. In this paper, we present an experimental work of fabrication of microchannels on an aluminium alloy 6061 surfaces by using a low power (<4 W) 400 fs laser system. The dimensional accuracy of the fabricated microchannels is assessed using scanning electron microscopy and 3D profilometry. Furthermore, as processing speed and scale is of importance in industrial laser processes, the use of scanning optics is examined as a means of developing a rapid and scalable ultrafast laser process.

Abstract: Nanoscale dispersoids will retard or inhibit recrystallization of aluminum alloys during thermomechanical processes. In the present study, the influence of an addition of 0.6 wt. % Cu on the precipitation behavior of dispersoids in an Al-Mg-Si-Mn-Cr alloy had been investigated. Large amounts of dispersoids with different shapes, e.g. cubic, rod-like and plate-like, were achieved in the experimental alloys after homogenization. Compared with the Cu-free alloy, Cu-added alloy exhibits a higher proportion of cubic shape dispersoid. HRTEM results indicated that the cubic shape dispersoid has an icosahedral quasicrystal structure, while the rod-like or plate-like shape dispersoids show a simple cubic crystal structure. Due to the presence of a high number density of quasicrystalline dispersoids, the Cu-added alloy exhibits a higher recrystallization resistance during hot compression. This study presents a new insight that besides the precipitation strengthening, the Cu alloying in an Al-Mg-Si-Mn-Cr alloy can also contributes to the precipitation of dispersoids.

Abstract: This contribution presents a study on the effect of heating rate maintained during annealing treatment on the final microstructure and mechanical properties of cold rolled Al1050 sheet. This study is focused on microstructure and texture evolution of Al1050 annealed at various heating rates, annealing temperatures, and holding times. It was observed that the longer exposure time for deformed microstructure affects the Vickers hardness values, grain size, and texture intensity. It seems that the crystallographic texture evolution is not affected by heating rate on quantitative level since the same set of orientations tended to evolve in all studied cases. The sample annealed at slow heating rate in a box-type furnace produced recrystallized microstructure with fine grain size, and comparatively lower texture intensity & hardness.

Abstract: Al-Mg alloys processed by Severe Plastic Deformation (SPD) have higher strength due to grain refinement by dynamic recrystallization. Generally, the relationship between grain size and strength is expressed by the Hall-Petch relationship, but the strength of Al-Mg alloys processed by SPD is higher than expected from the Hall-Petch extrapolation. This phenomenon is called ``Extra-Hardening. In this study, Al-3mass%Mg alloys processed by SPD were annealed, and the fraction of grain boundaries was measured by EBSD to determine the effect of grain boundaries on the strength. The results suggest that Extra-Hardening may be an effect of strengthening by SGB, which changes significantly with the number of passes and annealing, and constant LAGB strengthening. Strength predictions using the fraction of grain boundaries were in good agreement.