Effect of Cu addition on microstructures and tensile properties of high-pressure die-casting Al-5.5Mg-0.7Mn alloy

In this study, Cu was added into the high-pressure die-casting Al-5.5Mg-0.7Mn (wt%) alloy to improve the tensile properties. The effects of Cu addition on the microstructures, mechanical properties of the Al-5.5Mg-0.7Mn alloys under both as-cast and T5 treatment conditions have been investigated. Additions of 0.5 wt%, 0.8 wt% and 1.5 wt% Cu can lead to the formation of irregular-shaped Al₂CuMg particles distributed along the grain boundaries in the as-cast alloys. Furthermore, the rest of Cu can dissolve into the matrixes. The lath-shaped Al₂CuMg precipitates with a size of 15–20 nm × 2–4 nm were generated in the T5-treated Al-5.5Mg-0.7Mn-xCu (x = 0.5, 0.8, 1.5 wt%) alloys. The room temperature tensile and yield strengths of alloys increase with increasing the content of Cu. Increasing Cu content results in more Al₂CuMg phase formation along the grain boundaries, which causes more cracks during tensile deformation and lower ductility. Al-5.5Mg-0.7Mn-0.8Cu alloy exhibits excellent comprehensive tensile properties under both as-cast and T5-treated conditions. The yield strength of 179 MPa, the ultimate tensile strength of 303 MPa and the elongation of 8.7% were achieved in the as-cast Al-5.5Mg-0.7Mn-0.8Cu alloy, while the yield strength significantly was improved to 198 MPa after T5 treatment.     

Mechanical,forming and biological properties of Ti-Fe-Zr-Y alloys prepared by 3D printing

Biomedical Ti-Fe-Zr-Y alloys were prepared by 3D printing on pure titanium substrate. The influences of Zr on mechanical, forming, and biological properties of the alloys were investigated in detail. The results showed that with increasing the Zr addition, the surface roughness, friction coefficient and worn volume decrease at first and then increase, the lowest values obtained at 5.86 at.% Zr addition. The ultimate compression stress and specific strength gradually decrease. The studied alloys have no cytotoxicity. They can promote the early adhesion and proliferation of cells. The eutectic alloy with 5.86 at.% Zr addition has the best ability of apatite deposition, it exhibits a better comprehensive performance among the studied alloys, which is superior to the Ti_70.5Fe_29.5 and Ti-6Al-4 V alloys.     

Influence of cerium content on the corrosion behavior of Al-Co-Ce amorphous alloys in 0.6 M NaCl solution

The effect of cerium content on the corrosion behavior of Al-Co-Ce amorphous alloys in 0.6 M NaCl solution was investigated by cyclic polarization, Mott-Schottky and X-ray photoelectron spectroscopy techniques. Results indicated that the open circuit potential of Al-Co-Ce amorphous alloys displayed a decreased tendency with the increase in Ce content, and the amorphous alloy with 4 at.% Ce presented both the lowest passive current density and donor density indicating the best corrosion resistance, while adding excess Ce led to the reduced corrosion resistance of Al-Co-Ce alloys. Furthermore, it was found that a low Ce content is beneficial to the formation of a more protective passive film on Al-Co-Ce amorphous alloys, and the corrosion inhibition reactions of Al-Co-Ce alloys in 0.6 M NaCl solution were changed with the increase in Ce content and the detailed reasons were discussed.     

Effect of lubricants on warm compaction process of Cu-based composite

The use of lubricant is the key of warm compaction technology. Because of admixed different lubricants, the optimal parameters of warm compaction process were also different. This paper investigated the effect of two kind of lubricants (zinc stearate and polystyrene) on the parameters of warm compaction process by compared properties of Cu-based composite. It was shown that with the rise of compacting pressure, the density and hardness of the Cu-based composite increased, but the resistivity and gaining weight reduced. With increasing compacting temperature, the density and hardness first increased and then decreased, but the trend of resistivity and gaining weight just reversed. For the samples admixed zinc stearate (ZS), the optimal admixed concentration was 0.4 wt%, and the sample prepared at 120 °C and 650 MPa had the highest density and hardness, the lowest resistivity and gaining weight. For the samples admixed polystyrene (PS), these parameters were 0.7 wt%, 140 °C and 650 MPa, respectively. The properties of samples admixed PS were superior to that of admixed ZS.     

Nanostructured hydrogen storage materials prepared by high-energy reactive ball milling of magnesium and ferrovanadium

Hydrogen storage nanocomposites prepared by high energy reactive ball milling of magnesium and vanadium alloys in hydrogen (HRBM) are characterised by exceptionally fast hydrogenation rates and a significantly decreased hydride decomposition temperature. Replacement of vanadium in these materials with vanadium-rich Ferrovanadium (FeV, V80Fe20) is very cost efficient and is suggested as a durable way towards large scale applications of Mg-based hydrogen storage materials. The current work presents the results of the experimental study of Mg–(FeV) hydrogen storage nanocomposites prepared by HRBM of Mg powder and FeV (0–50 mol.%). The additives of FeV were shown to improve hydrogen sorption performance of Mg including facilitation of the hydrogenation during the HRBM and improvements of the dehydrogenation/re-hydrogenation kinetics. The improvements resemble the behaviour of pure vanadium metal, and the Mg–(FeV) nanocomposites exhibited a good stability of the hydrogen sorption performance during hydrogen absorption – desorption cycling at T = 350 °C caused by a stability of the cycling performance of the nanostructured FeV acting as a catalyst. Further improvement of the cycle stability including the increase of the reversible hydrogen storage capacity and acceleration of H₂ absorption kinetics during the cycling was observed for the composites containing carbon additives (activated carbon, graphite or multi-walled carbon nanotubes; 5 wt%), with the best performance achieved for activated carbon.     

Significant effect of TiF3 on the performance of 2NaAlH4+Ca(BH4)2 hydrogen storage properties

Titanium fluoride (TiF₃) is doped into the reactive hydride composite of 2NaAlH₄ + Ca(BH₄)₂ by ball milling to enhance the hydrogen storage properties of the composite system. NaAlH₄ and Ca(BH₄)₂ phases were fully transformed to Ca(AlH₄)₂ and NaBH₄ phases after the ball-milling process (6 h). Four major stages were discovered in the undoped and TiF₃-doped system, which is corresponding to; (i) Ca(AlH₄)₂, (ii) CaAlH₅, (iii) CaH₂ and (iv) NaBH₄, respectively. The addition of TiF₃ to the studied composite resulted in both reduced decomposition temperature and enhanced sorption kinetics compared with the undoped composite. The onset desorption temperature was reduced from 125 °C to 60 °C for the first stage in the TiF₃-doped composite, compared with the undoped composite. From differential scanning calorimetry analysis, the decomposition temperature for all stages has shifted to a lower temperature after doping with TiF₃. The activation energy has greatly reduced by 63.6 and 21.9 kJ/mol for CaAlH₅ and NaBH₄ stages, respectively, as compared with the undoped 2NaAlH₄ + Ca(BH₄)₂ composite. During the dehydrogenation process, the formation of new active species of Al₃Ti together with CaF₂ played a vital role in accelerating the reactions in 5 wt% TiF₃ doped to the studied composite system.     

Enhanced Mechanical Properties by Cyclic Compression in TiNb/Zr-Based Metallic Glassy Composite

A significant enhancement of yield strength and large plasticity was obtained in TiNb/Zr₅₅Cu₃₀Al₁₀Ni₅ composite by cyclic compression at the yield point. This phenomenon resulted from the cooperation of the metallic crystalline alloy TiNb and metallic glassy matrix Zr₅₅Cu₃₀Al₁₀Ni₅ in the composite. It was found that a large dislocation density of TiNb was produced during cyclic compression, which resulted in the increase of the strength. Meanwhile, the improvement of plasticity of the composite benefited from the propagation of excess shear bands in the glassy matrix, which were produced during the cyclic compression process. Hence, the collective effect of both resulted in the improved yield strength and large plasticity of the composite.     

Mechanical behavior and tensile/compressive strength asymmetry of ultrafine structured Ti–Nb–Ni–Co–Al alloys with bi-modal grain size distribution

Bulk ultrafine structured metallic materials with the bi-modal grain size distribution exhibit both high strength and good ductility. Here we show a new family of bi-modal Ti–Nb–Ni–Co–Al alloys. Their microstructure consists of an ultrafine structured eutectic matrix and relatively coarse β-Ti dendrites. Chemical modification of the parent Ti–Nb–Ni–Cu–Al system significantly affected type and volume fraction of matrix phases. In its turn, this influenced the deformation behavior. The unexpected “double yielding” behavior as well as tensile/compressive fracture strength asymmetry of the designed alloys are discussed in detail. For that, the microstructure alterations under compressive and tensile loading was in situ and ex situ analyzed by scanning electron microscopy.