Transactions of Nonferrous Metals Society of China最新文献

The synergistic impact of mechanical ball milling and flue gas desulfurization (FGD) gypsum on the dealkalization of bauxite residue was investigated through integrated analyses of solution chemistry, mineralogy, and microtopography. The results showed a significant decrease in Na₂O content (>30 wt.%) of FGD gypsum-treated bauxite residue after 30 min of mechanical ball milling. Mechanical ball milling resulted in differentiation of the elemental distribution, modification of the minerals in crystalline structure, and promotion in the dissolution of alkaline minerals, thus enhancing the acid neutralization capacity of bauxite residue. 5 wt.% FGD gypsum combined with 30 min mechanical ball milling was optimal for the dealkalization of bauxite residue.

The effect of addition temperature of MgO particles (MgO_p) on their dispersion behavior and the efficiency of grain refinement in AZ31 Mg alloy was investigated. In addition, the grain refinement mechanism was systematically studied by microstructure characterization, thermodynamic calculation, and analysis of solidification curves. The results show that the grain size of AZ31 Mg alloy initially decreases and then increases as the MgO_p addition temperature is increased from 720 to 810 °C, exhibiting a minimum value of 136 μm at 780 °C. The improved grain refinement efficiency with increasing MgO_p addition temperature can be attributed to the reduced Mg melt viscosity and enhanced wettability between MgO_p and Mg melt. Furthermore, a corresponding physical model describing the solidification behavior and grain refinement mechanism was proposed.

To accelerate the development and design of magnesium (Mg) alloys, the structural and mechanical properties of important precipitates in Mg−Zn alloys were studied by experiments and density functional theory. The nano-indentation tests revealed that the hardness of the precipitates initially increased and then decreased with increasing Zn content, and was significantly higher than that of pure Mg and Zn. The calculation results revealed that the precipitates stability initially increased and then decreased with increasing Zn concentration. The bulk moduli of the precipitates increased, whereas their shear and Young’s moduli initially increased and then decreased with increasing Zn content. The decreasing order of ductility for these compounds is MgZn₂ > Mg₂₁Zn₂₅ > Mg₂Zn₁₁ > Mg₄Zn₇. The surface profiles of the compounds revealed that they are obvious anisotropy. Both the degree of covalency and bond length of covalent bonds initially increased and then decreased with increasing Zn content.

Effects of ultrasonic vibration (UV) and mechanical vibration (MV) on the Mn-rich phase modification and mechanical properties of Al−12Si−4Cu−1Ni−1Mg−2Mn piston alloys were investigated. The results show that the UV and UV+MV treatments can significantly refine and fragmentize the microstructures. In addition, UV treatment can significantly passivate the primary Mn-rich Al₁₅Mn₃Si₂ intermetallics. The formation mechanisms of refinement and passivation of the grains and non-dendrite particles were discussed. Compared with the gravity die-cast alloys, the UV and UV+MV treated alloys exhibit improved tensile and creep resistance at room and elevated temperatures. These results can be attributed to the refinement of the α(Al) grains and the secondary intermetallics, the increased proportion of refined heat-resistant precipitates, and the formation of nano-sized Si particles. The ultimate tensile strength of the UV treated alloys at 350 °C exceeds that of commercial piston alloys. This indicates the high application potential of the developed piston alloys in density diesel engines.

A validated numerical model was established to simulate gas−liquid flow behaviors in the oxygen-enriched side-blown bath furnace. This model included the slip velocity between phases and the gas thermal expansion effect. Its modeling results were verified with theoretical correlations and experiments, and the nozzle-eroded states in practice were also involved in the analysis. Through comparison, it is confirmed that the thermal expansion effect influences the flow pattern significantly, which may lead to the backward motion of airflow and create a potential risk to production safety. Consequently, the influences of air injection velocity and furnace width on airflow behavior were investigated to provide operating and design guidance. It is found that the thin layer melt, which avoids high-rate oxygen airflow eroding nozzles, shrinks as the injection velocity increases, but safety can be guaranteed when the velocity ranges from 175 to 275 m/s. Moreover, the isoline patterns and heights of thin layers change slightly when the furnace width increases from 2.2 to 2.8 m, indicating that the furnace width shows a limited influence on production safety.

The effects of laser shock peening (LSP) on the microstructural evolution and mechanical properties of the Ti6242 alloy, including the residual stress, surface roughness, Vickers microhardness, tensile mechanical response, and high-cycle fatigue properties, were studied. The results showed that the LSP induced residual compressive stresses on the surface and near surface of the material. The maximum surface residual compressive stress was −661 MPa, and the compressive-stress-affected depth was greater than 1000 μm. The roughness and Vickers micro-hardness increased with the number of shocks, and the maximum hardness-affected depth was about 700 μm after three LSP treatments. LSP enhanced the fraction of low-angle grain boundaries, changed the grain preferred orientations, and notably increased the pole density of α phase on the near surface from 2.41 to 3.46. The surface hardness values of the LSP samples increased with the increase of the number of shocks due to work hardening, while the LSP had a limited effect on the tensile properties. The high-cycle fatigue life of the LSP-treated sample was significantly enhanced by more than 20% compared with that of the untreated sample, which was caused by the suppression of the initiation and propagation of fatigue cracks.

Beta Ti−35Nb sandwich-structured composites with various reinforcing layers were designed and produced using additive manufacturing (AM) to achieve a balance between light weight and high strength. The impact of reinforcing layers on the compressive deformation behavior of porous composites was investigated through micro- computed tomography (Micro-CT) and finite element method (FEM) analyses. The results indicate that the addition of reinforcement layers to sandwich structures can significantly enhance the compressive yield strength and energy absorption capacity of porous metal structures; Micro-CT in-situ observation shows that the strain of the porous structure without the reinforcing layer is concentrated in the middle region, while the strain of the porous structure with the reinforcing layer is uniformly distributed; FEM analysis reveals that the reinforcing layers can alter stress distribution and reduce stress concentration, thereby promoting uniform deformation of the porous structure. The addition of reinforcing layer increases the compressive yield strength of sandwich-structured composite materials by 124% under the condition of limited reduction of porosity, and the yield strength increases from 4.6 to 10.3 MPa.

Thermodynamic and kinetic aspects of Sn nucleation and growth processes onto a glassy carbon electrode from SnCl₂·2H₂O dissolved in ethylene glycol solutions were studied. Typical reduction and oxidation peaks observed in voltammograms have demonstrated the capability of ethylene glycol solutions to electrodeposit Sn. The temperature-dependence of diffusion coefficient values derived from potentiodynamic and potentiostatic studies helped to determine and validate estimations of the activation energy for Sn(II) bulk diffusion. Chronoamperometric results have identified that, the suitable model to describe the early stage of Sn electrodeposition could be composed of Sn three-dimensional nucleation and diffusion-controlled growth and water reduction contributions, which was duly validated by theoretical and experimental approaches. From the model, typical kinetic parameters such as the nucleation frequency of Sn (A), number density of Sn nuclei (N₀), and diffusion coefficient of Sn(II) ions (D), were determined. The presence of Sn nuclei with excellent quality and their structures were verified using SEM, EDX, and XRD techniques.

In order to increase the processability and process window of the selective laser melting (SLM)-fabricated Al−Mn−Mg−Er−Zr alloy, a novel Si-modified Al−Mn−Mg−Er−Zr alloy was designed. The effect of Si alloying on the surface quality, processability, microstructure, and mechanical properties of the SLM-fabricated alloy was studied. The results showed that introducing Si into the Al−Mn−Mg−Er−Zr alloy prevented balling and keyhole formation, refined the grain size, and reduced the solidification temperature, which eliminated cracks and increased the processability and process window of the alloy. The maximum relative density of the SLM-fabricated Si/Al−Mn−Mg−Er−Zr alloy reached 99.6%. The yield strength and ultimate tensile strength of the alloy were (371±7) MPa and (518±6) MPa, respectively. These values were higher than those of the SLM-fabricated Al−Mn−Mg−Er−Zr and other Sc-free Al−Mg-based alloys.

Undercooling solidification under a magnetic field (UMF) is an effective way to tailor the microstructure and properties of Co-based alloys. In this study, by attributing to the UMF treatment, the strength−ductility trade-off dilemma in GH605 superalloy is successfully overcome. The UMF treatment can effectively refine the grains and increase the solid solubility, leading to the high yield strength. The main deformation mechanism in the as-forged alloy is dislocation slipping. By contrast, multiple deformation mechanisms, including stacking faults, twining, dislocation slipping, and their strong interactions are activated in the UMF-treated sample during compression deformation, which enhances the strength and ductility simultaneously. In addition, the precipitation of hard Laves phases along the grain boundaries can be obtained after UMF treatment, hindering crack propagation during compression deformation.