A low-cost Mg–Al–Mn–Zn alloy for automotive road wheel applications Zhan, Hongyi; Zhang, Jianyue; Miao, Jiashi ...
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
April 2024, 2024-04-00, Letnik:
897
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In this study, a new Mg–Al–Mn–Zn alloy (AMZ211) was designed, aided by thermodynamic modeling, for applications in automotive road wheels using forging and flow-forming processes. The AMZ211 alloy ...was cast and forged in an industrial scale to obtain a forged blank to evaluate its tensile properties and hot formability under high-strain-rates (simulating flow-forming conditions). Multiple characterization techniques, including optical, scanning electron and scanning transmission electron microscopy as well as electron backscatter diffraction, were applied to investigate the microstructural evolution during the processing route. As expected from the alloy design, nano-sized Mn-containing dispersoids formed in a homogeneous manner during homogenization heat treatment, contributing to the formation of refined dynamically recrystallized (DRXed) grains in as-forged microstructure. The as-forged AMZ211 alloy showed better hot formability than as-forged AZ80 Mg alloy under high-strain-rate condition as well as a comparable strength property in relative to the benchmark and more expensive Mg–Zn–Zr alloys. The lower ductility of as-forged AMZ211 alloy may be due to the high twinning tendency of coarse unDRXed domains which were formed as a result of the original coarse-grained microstructure from solidification. The present study provides a low-cost Mg alloy for high-volume automotive road wheel applications.
Secondary phases, either introduced by alloying or heat treatment, are commonly present in most high-entropy alloys (HEAs). Understanding the formation of secondary phases at high temperatures, and ...their effect on mechanical properties, is a critical issue that is undertaken in the present study, using the AlxCoCrFeNi (x = 0.3, 0.5, and 0.7) as a model alloy. The in-situ transmission-electron-microscopy (TEM) heating observation, an atom-probe-tomography (APT) study for the reference starting materials (Al0.3 and Al0.5 alloys), and thermodynamic calculations for all three alloys, are performed to investigate (1) the aluminum effect on the secondary-phase fractions, (2) the annealing-twinning formation in the face-centered-cubic (FCC) matrix, (3) the strengthening effect of the secondary ordered body-centered-cubic (B2) phase, and (4) the nucleation path of the σ secondary phase thoroughly. The present work will substantially optimize the alloy design of HEAs and facilitate applications of HEAs to a wide temperature range.
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•Gas tungsten arc welding was used to join an as-cast AlCoCrFeNi2.1 eutectic high entropy alloy.•No welding defects were observed.•Synchrotron X-ray diffraction, electron microscopy ...and thermodynamic calculations used to evaluate the joint microstructure.•The fusion zone exhibits the highest hardness due to a refined interlamellar thickness.•The welded joints present a good strength/ductility balance.
The AlCoCrFeNi2.1 eutectic high entropy alloy is of great interest due to its unique mechanical properties combining both high strength and plasticity. Here, gas tungsten arc welding was performed for the first time on an as-cast AlCoCrFeNi2.1 alloy. The microstructural evolution of the welded joints was assessed by combining electron microscopy with electron backscatter diffraction, synchrotron X-ray diffraction analysis and thermodynamic calculations. Microhardness mapping and tensile testing coupled with digital image correlation were used to investigate the strength distribution across the joint. The base material, heat affected zone and fusion zone are composed of an FCC + B2 BCC eutectic structure, although the relative volume fractions vary across the joint owing to the weld thermal cycle. The BCC nanoprecipitates that existed in the base material started to dissolve into the matrix in the heat affected zone and closer to the fusion zone boundary. Compared to the as-cast base material, the fusion zone evidenced grain refinement owing to the higher cooling rate experienced during solidification. This translates into an increased hardness in this region. The joints exhibit good strength/ductility balance with failure occurring in the base material. This work establishes the potential for using arc-based welding for joining eutectic high entropy alloys.
Thermodynamic modelling is essential to understand the effect of binder composition on hydrate assemblage in modern Portland composite cements and its effect on durability. Binary and ternary plots ...of the hydrates' volumes can visualize the effect of different SCMs at different hydration times. The pore solution data analysis and the derived saturation indices can be used to gain further insights into the processes governing the dissolution and precipitation of hydrates. The modelling of the hydrated cements exposed to different environments has contributed significantly to the understanding of the determining factors governing sulfate, chloride and carbonate attack.
Thermodynamics models and modelling approaches have achieved a mature level. In the last years, more thermodynamic data have become available making thermodynamic calculations more reliable. The main gaps identified include the refinement of models describing the uptake of ions and water by C-S-H, as well as data for ASR products and zeolites.
The epoxidation of methyl esters found in Camelina sativa (CS) non-edible oil — largely containing unsaturated fatty acids — was performed. Epoxides are known to be used in biopolymer formation and ...CO2 capture. This study distinctively demonstrates epoxidation process through a combination of statistical methods and quantum chemical thermodynamic calculations. Esters produced along with glycerol during transesterification of vegetable oils can be used efficiently through epoxidation. Epoxidation products synthesized at various reaction conditions (including oil refinement) were analyzed through gas chromatography with mass spectrometry. According to the statistical analysis, the reaction time and temperature had the highest effect on the composition of products and oil refining is unnecessary. Moreover, iodine values (ester conversion) were determined without the use of chemicals through Raman spectroscopy. The study findings indicate CS epoxidation to be an environment-friendly process.
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The SPS reactive sintering of SiC/Ti3SiC2 composites with high SiC contents was studied by adding SiC to reactive (2TiC+1Ti+1.2Si+0.2Al) or (3TiC+2.2Si+0.2Al) mixtures. Four final volume percentages ...of SiC were targeted: 21 %, 50 %, 60 % and 70 % by adding the appropriate amounts of a micro-sized SiC powder to the reactive mixtures. The synthesis and the sintering of SiC/Ti3SiC2 composites were realized at 1500 °C/15 min/50 MPa from these mixtures. Due to liquid losses and SiO volatilization, the silicon lack was proven to be a significant limitation in the synthesis of Ti3SiC2 + nSiC composites. A deleterious effect of SiC additions was evidenced on both the reaction and the densification. Finally, Ti3SiC2 + nSiC composites were successfully obtained up to 50 vol% and 60 vol% of SiC from the (2TiC+1Ti+1.2Si+0.2Al) and (3TiC+2.2Si+0.2Al) mixtures, respectively. The thermodynamic calculations showed that the driving force of formation of SiC was very high which could disturb the syntheses from the (3TiC+2.2Si+0.2Al) mixture.
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•Dissimilar laser welds between NiTi and Ti6Al4V exhibiting the NiTi superelasticity and sustaining stress and elongation up to 520 MPa and 5.6 % were achieved using Pd ...interlayer.•The Pd interlayer significantly lowered the volume fraction of the brittle Ti2Ni intermetallic compound from 83 to 10 %.•The higher thermodynamic formation potential of Ti-Pd compounds than the Ti-Ni compounds facilitated the formation of TiPd and Ti2Pd compounds at the expense of Ti2Ni.•The accumulated irrecoverable strain on the dissimilar joint was below 1% after 30 load/unload cycles.
Obtaining a reliable NiTi to Ti6Al4V dissimilar joint exhibiting NiTi's superelasticity can provide design flexibility in aerospace and biomedical fields via integrating distinct material benefits. However, this materials couple is vulnerable to severe embrittlement due to the development of excessive intermetallic compounds (IMCs), namely Ti2Ni. Pd-free and Pd-interlayered NiTi-Ti6Al4V laser joints were evaluated for their microstructure, compositional changes, thermodynamic mechanism, and mechanical properties. The presence of Pd constrained the formation of Ti2Ni IMC, and NiTi-Ti6Al4V joints with excellent mechanical properties demonstrating superelastic behavior were achieved for the first time. The tensile strength and rupture strain of the Pd-added NiTi-Ti6Al4V joint improved more than twofold, reaching 520 MPa and 5.6%, respectively. During cyclic tensile testing, the Pd-added joint demonstrated superelasticity and a comparable irrecoverable strain to NiTi (1 versus 0.65%). Multiscale characterization revealed that the fraction of Ti2Ni decreased from 83 to 10% near the NiTi boundary and 24 to 6% at the weld center compared to the Pd-free joint. The superior thermodynamic formation tendency of Ti-Pd compounds over Ti2Ni IMC favored their development, and thus Ti-Pd and NiTi compounds dominated the fusion zone (FZ) at the expense of Ti2Ni IMC, explaining the improved mechanical performance of the Pd-added joint.
In this work, laser welding of a rolled CoCrFeMnNi high entropy alloy to 316 stainless steel was performed. Defect-free joints were obtained. The microstructure evolution across the welded joints was ...assessed and rationalized by coupling electron microscopy, high energy synchrotron X-ray diffraction, mechanical property evaluation, and thermodynamic calculations. The fusion zone microstructure was composed of a single FCC phase, and a hardness increase at this location was observed. Such results can be attributed to the formation of a new solid solution (arising from the mixing of the two base materials). Moreover, the incorporation of carbon in the fusion zone upon melting of the stainless steel also aids in the strengthening effect observed. The welded joints presented good mechanical properties, with fracture occurring at the fusion zone. This can be ascribed to the non-favourable, i.e., large grain size, microstructure that developed at this location.
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The stacking fault energy is closely related to structural phase transformations and can help to understand plastic deformation mechanisms in materials. Here we perform first principles calculations ...of the stacking fault energy in the face centered cubic (fcc) Cobalt-based binary alloys Co1−x Mx, where M = Cr, Fe, Ni, Mo, Ru, Rh, Pd and W. We investigate the concentration range between 0 and 30 at.% of the alloying element. The results are discussed in connection to the phase transition between the low-temperature hexagonal close packed (hcp) and the fcc structures observed in Co and its alloys. By analyzing the stacking fault energies, we show that alloying Co with Cr, Ru, and Rh promotes the hcp phase formation while Fe, Ni and Pd favor the fcc phase instead. The effect of Mo and W on the phase transition differs from the other elements, that is, for concentrations below 10% the intrinsic stacking fault energy is lower than that for pure fcc Co and the energy barrier is higher, whereas above 10% the situation reverses. We carry out also thermodynamic calculations using the ThermoCalc software. The trends of the ab initio stacking fault energy are found to agree well with those of the molar Gibbs energy differences and the phase transition temperature in the binary phase diagrams and give a solid support for the phase stability of these alloys.
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Alkali–silica reaction (ASR) is a major concrete durability problem, resulting in significant maintenance and reconstruction costs to concrete infrastructures all over the world. Despite decades of ...study, the underlying chemical and physical reaction mechanisms remain poorly understood, especially at molecular to micro-scale levels, and this has resulted in the inability to efficiently assess the risk, predict the service life, and mitigate deterioration in ASR-susceptible structures. This paper intends to summarize the current state of understanding and the existing knowledge gaps with respect to reaction mechanisms and the roles of aggregate properties (e.g., composition, mineralogy, size, and surface characteristics), pore solution composition (e.g., pH, alkalis, calcium, aluminum), and exposure conditions (e.g., temperature, humidity) on the rate and magnitude of ASR. In addition, the current state of computer modeling as an alternative or supplement to physical testing for prediction of ASR performance is discussed.
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