Effect of transition metal on the hydrogen storage properties of Mg–Al alloy

Mg–Al alloys were prepared via sintering combined with ball milling, and the effect of a transition metal (TM = Ti, V, Ni) on the hydrogen storage properties of these alloys was investigated; the alloys were characterized via X-ray diffraction, pressure composition isotherms, and differential scanning calorimetry. The results showed that the alloys were mainly composed of Mg and the Mg₁₇Al₁₂ phase, and the cell volume of these phases decreased after the addition of TM (TM = Ti, V, Ni), which is attributed to the improved hydrogenation kinetics of Mg–Al alloy. Moreover, the hydrogenation/dehydrogenation temperature of the Mg–Al alloy decreased with the addition of TM (TM = Ti, V, Ni). Ti, Ni, and V acted as a catalyst, thereby lowering the reaction barrier for dehydrogenation and promoting the reversible hydrogenation reaction of the Mg–Al alloy. The onset temperature of dehydrogenation of the Mg–Al–V alloy was ~244 °C, which was 66 °C lower than that of the Mg–Al alloy (~310 °C). And the apparent activation energy of the Mg–Al–V alloy was 80.1 kJ mol^?1, where it was 34.6 kJ mol^?1 lower than that of Mg–Al alloy.     

NbCl5 and CrCl3 catalysts effect on synthesis and hydrogen storage performance of Mg–Ni–NiO composites

Two kinds of novel materials, Mg–1·6 mol%Ni–0·4 mol%NiO–2 mol%MCl (MCl = NbCl ₅ , CrCl ₃ ), along with Mg–1·6 mol%Ni–0·4 mol%NiO for comparison, were examined for their potential use in hydrogen storage applications, having been fabricated via cryomilling. The effects of NbCl ₅ and CrCl ₃ on hydrogen storage performance were investigated. A microstructure analysis showed that besides the main Mg and Ni phases, NiO and Mg ₂ Ni phases were present in all samples. MgCl ₂ was only found in halide-doped samples and NbO was only found in NbCl ₅ -doped samples after ball milling. The particle size decreased significantly after 7 h of cryomilling. MgH ₂ , Mg ₂ NiH ₄ and Mg ₂ NiH_0·3 were present in all the samples, while NbH ₂ was only observed in the NbCl ₅ -doped sample afterabsorption. The NbCl ₅ -containing composite exhibited a low onset absorption temperature of 323 K, which was 10 K lower than that of the no-halide doped catalyst. It absorbed 5·32 wt% of hydrogen in 370 s at 623 K under 4 MPa hydrogen pressure and can absorb 90% of its full hydrogen capacity in 50 s. Having an onset desorption temperature of 483 K in vacuum, the NbCl ₅ -containing composite desorbed hydrogen faster than the no-halide doped sample. The hydriding–dehydriding kinetics performance of the CrCl ₃ -doped sample did not improve, but it did exhibit a lower onset desorption temperature of 543 K under 0·1 MPa, which was 20 K lower than that of the no-halide doped sample. NbO, NiO and NbH ₂ played important roles in improving absorption and desorption performances.     

Effect of Al content on hot tearing behaviour of Mg–xAl–2Ca–2Sm alloys

Mg–xAl–2Ca–2Sm (x?=?3, 5, 9 and 15) alloys were tested using an ‘L’-shaped sand mould serving as a hot tearing testing system. The experimental results showed that the solidification range of the Mg–xAl–2Ca–2Sm alloys first decreased and then increased as the Al content was increased. Furthermore, by increasing the Al content, the dendritic arms of the α-Mg phase become more developed, and the hot tearing tendency of the Mg–xAl–2Ca–2Sm alloys increased. In addition, the variety of precipitated phases was seen to be affected by the Al content and the tendency for hot tearing depended on the precipitated phase. The tendency of the Mg–xAl–2Ca–2Sm alloys for hot tearing first decreased and then increased with increasing Al content.     

Effect of phosphorus segregation and Ni2Cr formation on hydrogen embrittlement in 70Ni–30Cr alloys

Abstract

The effects of aging at 773 K on hydrogen embrittlement in Ni–30Cr (wt-%) alloys having two levels of P have been investigated by considering the grain-boundary segregation of impurity atoms and the Ni₂ Cr ordered-phase formation. Aging at 773K suppressed intergraular fracture and reduced the susceptibility to hydrogen embrittlement in the low-P alloy. Such behaviour can be explained in terms of the grain-boundary strengthening caused by the segregation of C atoms. During aging at 773 K, the Ni₂Cr ordered phase formed and the deformation mode changed from wavy slips to coplanar slip with paired dislocations, and then to coplanar slip with microtwins. In the low-P alloy, this change of deformation mode induced step-like cracks which may have occurred by the separation of either the {111} slip planes or the microtwin interfaces. In the high-P alloy, aging for short times caused C segregation to the grain boundaries which suppressed intergranular fracture. However, aging for longer times induced drastic intergranular hydrogen embrittlement because of the grain-boundary segregation of P atoms, which offset the effect of the boundary strengthening caused by C atoms.

MST/177     

Effect of Al addition on the grain refinement and mechanical properties of as-cast Mg–5Y–4Sm alloys

Journal of Materials Science - In recent years, the utilization of Al as a grain refiner in Mg–RE alloys has gained widespread attention because of its advantages such as low cost. In this...     

Effect of aluminum on precipitation hardening in Cu–Ni–Zn alloys

The effect of aluminum on the precipitation hardening of Cu–Ni–Zn alloys with varying aging temperatures and times was investigated in this article, in the hope to achieve better mechanical properties. Vickers hardness, tensile, and electrical conductivity tests were carried out to characterize the properties of the Cu–Ni–Zn alloys with or without an addition of aluminum subjected to different aging treatments. The results show that an addition of 1.2 wt% aluminum can play an influential role in the precipitation hardening of the Cu–Ni–Zn alloys. For example, it can increase the peak hardness from 58 Hv for the solution-treated Cu–10Ni–20Zn alloy to 185 Hv for the solution-treated Cu–10Ni–20Zn–1.2Al alloy during aging at 500 °C. The yield strength, tensile strength, and electrical conductivity of the Cu–10Ni–20Zn–1.2Al alloy subjected to suitable treatments under prior cold-rolled and aged conditions can reach 889 MPa, 918 MPa, and 10.96% IACS, respectively, being much higher than those of the relevant alloy without aluminum and comparable to those of the Cu–Be alloys (C17200 and C17510). According to the transmission electron microscope observations, it was found that formation of nanosized precipitates with the L1₂-type ordered lattice results in precipitation hardening, and an orientation relationship of [011]_\textp//[011]_\textm [011]_{\text{p}}//[011]_{\text{m}} and (100)_\textp//(200)_\textm (100)_{\text{p}}//(200)_{\text{m}} exists between the precipitates and the α-Cu matrix.     

Effect of ultrasonic treatment on the mechanical behaviour of Al–Ni alloys

Applications of Al–Ni alloys are limited because their matrix is weaker than other binary aluminium alloys. Ultrasonic treatment (UST) is an effective tool for grain refinement that can strengthen the matrix phase. It not only reduces the grain size and porosity but also refines and uniformly distributes the secondary phase, which can influence the mechanical properties of Al–Ni alloys. Varying the amount of nickel (1, 2, 3, and 5?wt-%) in molten aluminium along with ultrasonication of the melt is investigated through grain-structure, mechanical properties, and fractography. Mechanical properties of the alloys subjected to UST are superior to respective as-cast alloys. UST also altered the fracture behaviour from dominant ductile fracture in as-cast alloys to dominant mixed mode fracture.     

Effect of Gd on physics properties of the dual-phase Ni–Mn–Ga-based alloys

The microstructure, martensitic transformation (MT) and shape memory effect (SME) of the dual-phase Ni₅₈Mn₂₅Ga_17?xGd_x (x?=?0, 0.1, 0.2, 0.5, 1) alloys have been investigated. The results show that the refined the grain size and adjust the distribution of γ phase by added rare earth Gd in the Ni₅₈Mn₂₅Ga_17?xGd_x alloys. With increasing Gd content, the MT temperatures of Ni₅₈Mn₂₅Ga_17?xGd_x alloys first gradually decrease and then increase with the increasing content of Gd, reaching their minimum values when the content of Gd is 0.5?at.-%. In addition, the Ni₅₈Mn₂₅Ga_16.9Gd_0.1 has a SME of 5.1% owing to the favourable γ phase distribution, which is mainly attributable to the γ phase grain refined and weaken resistance of reverse MT.     

Effect of extrusion parameters on properties of rapidly solidified Al–Mg powder alloys

Abstract

Three rapidly solidified Al–Mg powder alloys have been consolidated by means of cold compaction followed by hot extrusion. The extrusion conditions of temperature, reduction ratio, and ram speed were varied, and it was observed that the mechanical properties of the extrudates were strongly process related. Relationships between properties and the temperature compensated strain rates during extrusion have been established. These alloys have strength/density properties superior to the strongest conventional ingot cast alloys. Good fracture toughness has been recorded in the Al–7 Mg alloy and all three alloys possess good resistance to stress corrosion cracking.

MST/498     

Effect of Si content on microstructure and mechanical properties of Al–Si–Mg alloys

Microstructure and mechanical properties of as-cast and as-extruded Al–Si–Mg alloys with different Si content are investigated by tensile test, microstructure observation. High density of Si particles in the Al alloys can induce dynamic recrystallization during hot extrusion and it becomes more matured with an increase in the density of Si particles. The tensile strength of as-cast and as-extruded alloys can be improved with the increase of Si content and hot extrusion make the elongation of alloys increase dramatically. Considerable grain refining effect caused by recrystallization occurred during hot extrusion of S2 (equivalently commercial A356 alloy) and S3 (near eutectic alloy) alloys plays an important role in the improvement of elongation. A good combination of strength and elongation for the as-extruded S3 alloy indicates that near eutectic Al–Si alloys can be hot-extruded to produce aluminum profiles with high performance.     

Effect of Zn addition on hot tearing behaviour of Mg–0.5Ca–xZn alloys

The influence of Zn addition (0, 0.5, 1.5, 4.0 and 6.0 wt.%) on hot tearing behaviour of Mg–0.5 wt.% Ca alloy was investigated using a constrained rod casting (CRC) apparatus. The effects of mould temperature and grain refinement on the hot tearing susceptibility (HTS) were studied. Hot tears were observed with 3D X-ray tomography and the tear volumes were quantified. Results show that the Zn addition increases the HTS of Mg–0.5Ca alloys. At a mould temperature of 250 °C, all alloys investigated except Mg–0.5Ca–6Zn alloy show severe HTS. An increase in the mould temperature from 250 °C to 450 °C did not reduce the HTS in Mg–0.5Ca–1.5Zn and Mg–0.5Ca–4Zn alloys. Among all the investigated alloys, Mg–0.5Ca–4Zn alloy exhibits severe HTS as it completely broke away from the sprue–rod junction. The HTS of alloys was well correlated with the susceptible temperature range (ΔT_s). An increase in ΔT_s increased the HTS. The hot tears propagated along the grain boundaries through liquid film rupture. Grain refinement by Zr addition improved the hot tearing resistance of Mg–0.5Ca–4Zn alloy as the fine grain structure facilitated the easy feeding of liquid into the last area of solidification and accommodated the developed strain more effectively.     

Effect of multi-directional forging and ageing on fracture toughness of Al–Zn–Mg–Cu alloys

Strength, ductility and fracture toughness are the most important mechanical properties of engineering materials. In this work, an Al–Zn–Mg–Cu alloy was subjected to multi-directional forging (MF) and ageing treatment. Microstructural evolution was studied by optical and electron microscopy and strength, ductility and fracture toughness were researched. After MF, the dislocation density was increased and the microstructure was refined. The strength and fracture toughness were increased, while the ductility was decreased sharply. Without compromising the strength, the ductility was improved significantly after ageing. The fracture toughness was increased further. The coarse and discontinuously distributed grain boundary precipitates were found to be responsible for higher fracture toughness of the fine-grained structure Al–Zn–Mg–Cu alloy.     

Effects of samarium on microstructure and mechanical properties of Mg–Y–Sm–Zr alloys during thermo-mechanical treatments

Microstructure and mechanical properties of Mg–4Y–xSm–0.5Zr (x = 1, 4, 8) alloys during thermo-mechanical treatments were investigated in this study. Mg–4Y–4Sm–0.5Zr alloy exhibits higher tensile strength but lower elongation than Mg–4Y–1Sm–0.5Zr alloy during the thermo-mechanical treatments. Large amount of intermetallic phases still remained at grain boundaries in Mg–4Y–8Sm–0.5Zr alloy after solution. These undissolved phases can strengthen the grain boundaries at temperatures higher than 573 K. But the room temperature mechanical properties of Mg–4Y–8Sm–0.5Zr alloy during the thermo-mechanical treatments were greatly weakened for the brittleness of these undissolved intermetallic phases.     

Microstructure and internal friction of Ni–Ti alloys absorbing hydrogen

The microstructure and internal friction of Ni–Ti alloys after hydrogen absorption have been investigated by means of optical microscopy, X-ray diffraction, differential scanning calorimetry and low frequency torsional internal friction apparatus. The results show that, after hydrogen absorption, the grains tend to be elongated, and the nucleation and growth of hydrides are mainly concentrated at the grain boundaries. In addition, a new phase ultimately identified as Ti₂NiH_0·5 phase forms after absorption of hydrogen. The hydrogen induced martensite promotes the emergence of a two-stage transformation. However, the growth of hydrides causes a reduction of the hydrogen induced martensite. The hydrides act as strong pinning points, resulting in a dramatic increase in the internal friction. In addition, the marked change of the internal stress, caused by the microscopic strain and the mismatching of the volumes, also improves the internal friction.     

Effect of cooling rate and Mg content on the Al–Si eutectic for Al–Si–Cu–Mg alloys

This study investigates and clarifies the qualitative and quantitative effects of Mg content and cooling rate (ranging from 0.5 to 4 °C/s), on the modification of the silicon eutectic structure and on the undercooling of the silicon eutectic growth temperature (ΔT_Si-eut) in the series of Al–Si–Cu–Mg alloys. The critical Mg content to produce a notable improvement in the silicon eutectic by 1.5 modification levels (regardless of the cooling rate) is 0.6 wt.% Mg. A similar increase in the modification level was also observed when the cooling rate was increased to a maximum of 4 °C/s, regardless of the Mg content. Measurements of the area and roundness of the silicon particles showed a good correlation with the modification level. The undercooling (ΔT_Si-eut) increased by up to ~ 23 °C at a relatively high Mg content and cooling rate and up to ~ 14 °C when the Mg content was increased from 0.4 to 0.6 wt.%.     

Effect of thermal treatments on microstructure and impact toughness of die cast Mg–Al–Mn alloys

Abstract

A study of the effects of heat treatment on an Mg–Al–Mn alloy was carried out. Die cast AM60B alloy (Mg–6.0Al–>0.25Mn–<0.010Cu–<0.002Ni–<0.005Fe (wt-%)) specimens for microstructural investigation, tensile testing, and impact toughness testing, were produced using a multispecimen die in a high pressure, cold chamber apparatus. As cast specimens were studied either in their original condition or after they had been subjected to a direct aging treatment at 175°C. Solution treatment was also carried out, producing a T4 temper and a T6 temper by subsequent additional aging, and the resulting specimens examined. The investigation allowed evaluation of modifications to microstructural and mechanical properties produced by thermal treatments. In particular, the analysis of structure and solidification defect evolution showed that, despite an increase in void volume fraction and size induced by thermal treatments, a significant improvement of toughness during the crack growth process could be achieved with the appropriate tempers. Marked modifications to high strain rate loading conditions were detected, with improvements of total absorbed impact energy of up to 40% with respect to the as cast condition. This was associated with changes in fracture mechanisms, promoting a transition to a completely ductile mode in solution treated specimens.     

Effect of silver addition on formation of secondary phases in squeeze cast Al–Cu–Mg alloys

Abstract

The effect of silver addition on the formation of secondary phases in squeeze cast Al–4.0Cu–1.5Mg and Al–4.0Cu–1.5Mg–0.7Ag (all wt-%) alloys has been investigated using optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffractometry, and transmission electron microscopy. The as cast microstructure of both alloys consists of primary dendritic α-Al and various types of secondary solidification phase, e.g. Al₂Cu, Al₂CuMg, Al(Cu,Ag)Mg, and icosahedral (I) and decagonal (D) quasicrystalline phases. However, the solidification path in the interdendritic region during squeeze casting is different for each alloy, i.e. L→ternary α-Al–Al₂Cu–Al₂CuMg eutectic in Al–4.0Cu–1.5Mg and L→L′+Al₂Cu→α-Al–Al₂Cu–Al(Cu_0.75Ag_0.25)Mg eutectic in Al–4.0Cu–1.5Mg–0.7Ag. This indicates that silver acts as an alloying element stabilising the formation of Al(Cu,Ag)Mg Laves phase. The remaining copper and iron rich liquid in the interdendritic region at the final stage of solidification solidifies into a mixed structure of α-Al, Al₂Cu, and AlCuFe I (or D) phases. The composition of the I and D phases, measured by energy dispersive X-ray spectroscopy, is in the range Al–(27～28)Cu–(9～10)Fe and Al–(26～27)Cu–(7～9)Fe (all at.-%) respectively.     

Effect of grain refiner on the tensile and impact properties of Al–Si–Mg cast alloys

The present study aims to investigate the influence of the addition of Ti and B in the form of five different grain refiners/aluminium master alloys (Al–10%Ti, Al–5%Ti–1%B, Al–2.5%Ti–2.5%B, Al–1.7%Ti–1.4%B and Al–4%B) in conjunction with that of Sr (as modifier) added in the form of Al–10%Sr master alloy to A356.2 alloy. Grain refinement of an A356.2 alloy with Ti and B additions in the ranges of 0.02–0.5% and 0.01–0.5%, respectively, was examined using these different types of grain refiners. Strontium additions of 30 and 200 ppm were made. All alloys were T6-heat treated before mechanical testing. Tensile and impact tests were conducted to evaluate the influence of the interaction between grain refiner and modifier on the mechanical properties. The properties were determined for both the as-cast and heat-treated conditions.     

Effect of magnesium content on thermal and structural parameters of Al–Mg alloys directionally solidified

In this study, the influence of magnesium content on thermal and structural parameters during the unsteady-state unidirectional solidification of Al–Mg alloys is analyzed. Using a special device, Al–Mg alloys containing 5, 10, and 15 wt% Mg were submitted to unidirectional solidification. Using a data acquisition system, the temperature variations along the casting during solidification were measured. From these results, the variations of solidification parameters as growth rate of dendrite tips, thermal gradient, cooling rate, and local solidification time were determined. The variation of global heat transfer coefficient at metal/mould interface was estimated through the adjustment of experimental temperature variation close to the interface and numerical predictions. Primary and secondary dendrite arms spacing variations during solidification were measured by optical microscopy. From these results, comparative analysis were developed to determine the influence of magnesium content.