Formation and thermal stability of Ca–Mg–Zn and Ca–Mg–Zn–Cu bulk metallic glasses

Several Ca–Mg–Zn and Ca–Mg–Zn–Cu bulk metallic glasses were produced by copper mold casting method. The alloy compositions were selected using specific criteria recently identified by the authors. The glass transition temperature, crystallization temperature, temperature interval of the supercooled region, melting temperature as well as heats of crystallization, and melting are reported for these alloys.     

Characterisation and thermodynamic calculations of biodegradable Mg–2.2Zn–3.7Ce and Mg–Ca–2.2Zn–3.7Ce alloys

In the present study, the effect of Ca (0.5–6?wt-%) content on the microstructure, phase formation, and mechanical properties and in vitro degradation behaviour of Mg–2.2Zn–3.7Ce alloys were investigated. Microstructural analysis and thermodynamic calculations also showed that Mg–2.2Zn–3.7Ce alloy contain α-Mg, Mg₁₂Ce and CeMgZn₂, while after adding 0.5?wt-% Ca to Mg–2.2Zn–3.7Ce alloy, IM1 (Ca₃Mg_xZn_15?x) (4.6?≤?x?≤?12) phase was detected. Further addition of Ca to 6?wt-% resulted in forming Mg₂Ca besides α-Mg, Mg₁₂Ce and IM1 with the absence of CeMgZn₂. The tensile strength and elongation of the Mg–Ca–2.2Zn–3.7Ce alloys increase with increasing Ca content up to 1.5?wt-%, while further addition of Ca to 6?wt-% has a reversed effect. Similarly, the degradation rate of the alloys increased first with increasing Ca content and then decreased.     

Extrusion of AI–Zn–Mg–Cu–Zr alloys

Abstract

Four aluminium alloys of different zinc/magnesium ratio have been studied under various extrusion conditions. The alloys were cast in steel book moulds and subjected to initial thermomechanical treatments. Studies were made of hot extrusions and cold hydrostatic extrusions and in each case the changes in the extrusion parameters were analysed. An attempt has been made to explain some of the extrusion defects which appeared in various extruded sections. The extrusion speed was found to be crucial, since sections developed surface cracks at higher speeds. The extrusion speed was also found to vary inversely with the extrusion ratio, with higher speeds at low ratios. A well defined solute–depleted weld zone was observed on each of the four faces of a square tube extruded using a porthole die. Thermal treatment was not found to improve this weak weld zone. Tubes extruded using a floating-mandrel die withstood pressure testing up to 550 MPa.

MST/43     

Bulk magnetic studies on Cu–Mg–Zn ferrites

The ferrite compositions of Cu(0.5-x)MgxZn0.5Fe2O4 were synthesized by thermal decomposition of the solid solution of oxalate complexes obtained by the coprecipitation technique using oxalate precursors. X-ray diffraction (XRD) patterns of all the samples showed a single spinel phase with no detectable impurity phases. The magnetization values were measured by the superconducting quantum interference device (SQUID) technique and the observed variation in magnetization values is attributed to porosity present in these ferrite compositions. The saturation magnetization (Ms) versus temperature curves revealed the curve to be of type Q. The variation of saturation magnetization (Ms) with temperature (T) for composition x=0.25 and x=0.40 exhibited a type Q-curve at a higher field of 1000 G. The monotonic increase in Hc with grain diameter for ferrite compositions under investigation leads to HcD-1. Saturation magnetization (Ms) values of end ferrites sintered at 1000 °C are higher than those of oxalate complexes decomposed at 600 °C. © 1998 Kluwer Academic Publishers     

Precipitation hardening of Zr-modified Mg–Ca–Zn alloy

The microstructure and mechanical properties of Mg–Ca–Zn alloys with 1 wt.% Zr were investigated in as-cast and heat-treated conditions. A substantial decrease in grain size (from 65 μm for the Mg–Ca–Zn base alloy to 22 μm) was observed. The alloy was solution treated at 410 °C for up to 96 h followed by aging at 175 °C for up to 24 h. Conventional techniques, X-ray diffraction, EM + EDS, and TEM were used to characterize the microstructure of the alloy. The microstructure obtained after heat treatment had equiaxed grains with evenly distributed binary phase Zn₂Zr. The binary Mg₂Ca and ternary Mg₂Ca₆Zn₃ phases were identified in the matrix and at grain boundaries surrounded by precipitate-depleted zones (PDZs). The thermal stability of the Zr-modified alloys was examined by microhardness measurements conducted after prolonged exposures of the alloys to elevated temperatures. It was found that Zr is a structure-stabilizing factor. Its influence was associated with the formation of Zn₂Zr phase that does not undergo coarsening at the elevated temperatures used (due to the low diffusivity of Zr). The nanoscale mechanical properties of grain boundary PDZs were analyzed using combined nanoindentation and atomic force microscopy. These mechanical properties were then correlated to the composition and precipitate distribution in PDZs. An increase in the solution treatment duration from 10 to 96 h at 410 °C resulted in expansion of PDZs from ~0.75 to ~3 μm, while the following aging at 175 °C for up to 24 h did not lead to a detectable change in PDZs. The analysis indicates that the lowest hardness was found in the region where Zn₂Zr precipitates density was low, regardless of the solute concentration.     

Newly observed prismatic Mg2Sn laths in a Mg–Sn–Zn–Mn alloy

Lath-shaped Mg₂Sn precipitates with their habit planes parallel to the prismatic planes of the Mg matrix are characterized in a Mg–Sn–Zn–Mn alloy. The orientation relationships (ORs) between these β-Mg₂Sn precipitates and α-Mg matrix are [0 1 1]_β//[0 1 ?1 0]_α and (0 1 ?1)_β deviating 0.36° to 1.20° from (0 0 0 1)_α, in which the deviation angle of 0.39° is most frequently observed. Although the ORs vary, the laths always exhibit four side facets bearing fixed relationships with g vectors in reciprocal space. Their major side facets incline to the basal plane of Mg matrix from 4.3° to 14.3°.     

Mg–Gd–Y–Zn稀土镁合金应变调节机制研究

目的 在微观尺度上研究Mg–5.4Gd–1.8Y–1.5Zn合金的应变调节机制。方法 将拉伸试样变形至应变为6%,采用基于互相关分析的高分辨EBSD技术测量材料内部的刚体转动张量以及几何必需位错密度。结果 Mg–Gd–Y–Zn合金主要由基面<a>位错以及锥面<c+a>位错调节应变,即使在软取向晶粒内,锥面<c+a>位错也会大量出现。当发生基面–基面位错的滑移转移与基面–锥面位错的滑移转移时,相邻两晶粒滑移系之间的Luster–Morris因子很高(>0.78)。结论 随着不同滑移系施密特因子的升高,晶粒内的位错密度逐渐降低。这一反常现象可以归因于硬取向晶粒变形需消耗更多的应变能,而这部分应变能以位错密度的形式储存在晶粒内。     

Microstructure and magnetic studies of Mg–Ni–Zn–Cu ferrites

Soft Mg–Ni–Zn–Cu spinel ferrites having general chemical formula Ni_xMg_0.5−xCu_0.1Zn_0.4Fe₂O₄ (where x = 0.1, 0.2, 0.3, 0.4 and 0.5) were prepared by standard double sintering ceramic method. The samples were characterized by X-ray diffraction at room temperature. The X-ray diffraction (XRD) study revealed that lattice parameter decreases with increase in Ni content, resulting in a reduction in lattice strain. The electrical and magnetic properties of the synthesized ferrites have been investigated as a function of temperature. The variation of initial permeability and AC susceptibility with temperature exhibits normal ferrimagnetic behavior. The variation of initial permeability with frequency is studied. The Curie temperature (T_C) in the present work was determined from initial permeability and AC susceptibility. The Curie temperature increases with Ni content.     

High-pressure homogenization treatment of Al–Zn–Mg–Cu aluminum alloy

Absract The microstructures and aging hardening response of Al–12Zn–3.5Mg–3.0Cu–0.14Zr aluminum alloy after a high-pressure homogenization treatment at 750 °C for 45 min under 5 GPa were investigated. The results showed that the constituent phases dissolved completely and formed α-Al single-phase solid solution comparable to that formed after ambient-pressure homogenization at 450 °C/96 h + 460 °C/128 h. The complete dissolution of the constituent phases increased the solubility of the alloying elements, as well with the over-burning temperature and aging hardness.     

The paint–bake response of three Al–Mg–Zn alloys

The aging behaviors of three Al–Mg–Zn alloys have been investigated under conditions similar to the paint–bake cycle currently used in automotive manufacturing. The three alloys contain Mg in atomic concentrations from one to two times those of Zn. Natural aging at 25 °C after solutionizing is found to produce a linear increase in hardness with logarithmic time for times of up to 1 year. Hardnesses in naturally and artificially aged conditions are found to increase with Mg content. Artificial aging at 175 °C for 30 min, which simulates the automotive paint–bake cycle, produces increases in hardness of 15–36% over the solution-treated conditions. Peak hardness from artificial aging at 175 °C is produced in all alloys after approximately 8 h. Natural aging for 10 days prior to artificial aging at 175 °C does not produce significant changes in hardness compared with artificial aging alone. Natural aging for 1 year after simulated paint–bake aging increases hardnesses by 41–78% over those after simulated paint–bake aging alone. The precipitation strengthening mechanism in these alloys is consistent with η′ formation. Increases in hardness and strength with increasing Mg content are consistent with increased solid–solution strengthening, which is retained even after artificial aging.     

Microstructural evolution of Al–Zn–Mg–Cu alloy during homogenization

In this study, the microstructural evolution of an as-cast Al–Zn–Mg–Cu alloy (AA7085) during various homogenization schemes is investigated. It is found that in a single-stage homogenization scheme, some of the primary eutectic gets transformed into the Al₂CuMg phase at 400 °C, and the primary eutectic and Al₂Cu phase gradually dissolve into the alloy matrix at 450 °C. The Al₃Zr particles are mainly precipitated at the center of the grain because Zr is peritectic. However, the homogeneous distribution of the Al₃Zr particles improves and the fraction of Al₃Zr particles increases in two-stage homogenization scheme. At the first low-temperature (e.g., 400 °C) stage, the Al₃Zr particles are homogeneously precipitated at the center of the grain by homogeneous nucleation and may be heterogeneously nucleated on the residual second-phase particles at the grain boundary regions. At the second elevated-temperature (e.g., 470 °C) stage, the Al₃Zr nuclei become larger. A suitable two-stage homogenization scheme for the present 7085-type Al alloy is 400 °C/12 h + 470 °C/12 h.     

Microstructure,mechanical properties and machinability of Cu–Zn–Mg and Cu–Zn–Sb brass alloys

Lead-free alloys have attracted great attentions recently due to the toxic nature of lead for the human body. In this study, low amounts of Mg and Sb were added to the Cu65–Zn35 brass and microstructure, mechanical properties and machinability of samples were compared to Cu65–Zn35 brass. Both Mg and Sb led to the promotion of β′ phase as well as the formation of new ternary copper rich intermetallic particles. It was found that these particles had a significant role in the reduction of the ultimate tensile strength, toughness, work hardening and elongation while increasing the hardness of samples. Results of machinability evaluation of samples showed that the cutting forces were decreased significantly and morphology of chips were improved compared to Cu65–Zn35 brass sample.     

Microstructure and Peritectic Reaction within As-solidified Mg–Zn–Y Alloy

An investigation on the microstructure and peritectic reaction involving icosahedra phase （I-phase） and crystalline phase （W-phase） within Mg-Zn-Y alloy during conventional solidification technology and rapid quenching was carried out, The solidification process of the peritectic reaction is discussed in details, It is shown that there is no obvious crystallographic relationship between the W-phase and I-phase during the solidification of Mg-Zn-Y alloy.     

Mechanical and bio-corrosion properties of quaternary Mg–Ca–Mn–Zn alloys compared with binary Mg–Ca alloys

Binary Mg–xCa alloys and the quaternary Mg–Ca–Mn–xZn were studied to investigate their bio-corrosion and mechanical properties. The surface morphology of specimens was characterized by X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results of mechanical properties show that the yield strength (YS), ultimate tensile strength (UTS) and elongation of quaternary alloy increased significantly with the addition of zinc (Zn) up to 4 wt.%. However, further addition of Zn content beyond 4 wt.% did not improve yield strength and ultimate tensile strength. In contrast, increasing calcium (Ca) content has a deleterious effect on binary Mg–Ca alloys. Compression tests of the magnesium (Mg) alloys revealed that the compression strength of quaternary alloy was higher than that of binary alloy. However, binary Mg–Ca alloy showed higher reduction in compression strength after immersion in simulated body fluid. The bio-corrosion behaviour of the binary and quaternary Mg alloys were investigated using immersion tests and electrochemical tests. Electrochemical tests shows that the corrosion potential (E_corr) of binary Mg–2Ca significantly shifted toward nobeler direction from −1996.8 to −1616.6 mV_SCE with the addition of 0.5 wt.% manganese (Mn) and 2 wt.% Zn content. However, further addition of Zn to 7 wt.% into quaternary alloy has the reverse effect. Immersion tests show that the quaternary alloy accompanied by two secondary phases presented higher corrosion resistance compared to binary alloys with single secondary phase. The degradation behaviour demonstrates that Mg–2Ca–0.5Mn–2Zn alloy had the lowest degradation rate among quaternary alloys. In contrast, the binary Mg–2Ca alloy demonstrated higher corrosion rates, with Mg–4Ca alloy having the highest rating. Our analysis showed the Mg–2Ca–0.5Mn–2Zn alloy with suitable mechanical properties and excellent corrosion resistance can be used as biodegradable implants.     

Correlation on the Electrical and Thermal Conductivity for Binary Mg–Al and Mg–Zn Alloys

In this work, the electrical resistivity and thermal conductivity of both as-solution binary Mg–Al and Mg–Zn alloys were investigated from 298 K to 448 K, and the correlation between the corresponding electrical conductivity and thermal conductivity of the alloys was analyzed. The electrical resistivity of the Mg–Al and Mg–Zn alloys increased linearly with composition at 298 K, 348 K, 398 K, and 448 K, while the thermal conductivity of the alloys exponentially decreased with composition. Moreover, the electrical resistivity and thermal conductivity for both Mg–Al and Mg–Zn alloys varied linearly with temperature. On the basis of the Smith–Palmer equation, the thermal conductivity of both binary Mg alloys was found to be correlated quite well with the electrical conductivity in the temperature range from 298 K to 448 K. The corresponding Lorenz number is equal to $2.162\times 10^{-8} \,\hbox {V}^{2}\cdot \hbox {K}^{-2}$ 2.162 × 10 - 8 V 2 · K - 2 , and the lattice thermal conductivity is equal to $5.111 \,\hbox {W}\cdot \hbox {m}^{-1}\cdot \hbox {K}^{-1}$ 5.111 W · m - 1 · K - 1 . The possible mechanisms are also discussed.     

Investigation of mechanical properties of advanced Al–Zn–Mg–Cu alloy

Abstract

The mechanical properties of the rapidly solidified 7000 series powder alloy CW 67 were investigated for various extrusion and heat treatment conditions. The principal aim of the work was to ascertain the optimum processing route for peak aged (T6) material. The highest proof stress in the T6 condition was found to be 572 MN m^?2 for material extruded at 325°C and aged for 13·5 h at 120°C after solutionising. The ductility of this material was found to be 13·5%. The fracture toughness was measured in two orientations and found to be approximately 21 MN m^?3/2 in the short transverse direction and 44 MN m^?3/2 in the longitudinal direction. Degassing and hot compaction was found to improve the fracture toughness of the material substantially.

MST/1504     

Prediction and characterization of growth temperatures in Al–Zn–Mg alloys

Growth temperatures of α-Al, intermetallic τ and eutectic α + τ phases in Al-12 wt.% Zn 6 wt.% Mg alloy has been determined as a function of growth velocity in the range of 3 × 10^? 5 to 1 × 10^? 3 m/s at a temperature gradient of 2500 K/m, using a directional solidification technique. The experimental results are found to be in good agreement with predictions of growth temperatures of competing constituents for multicomponent systems.     

Effects of Zn content on microstructures and mechanical properties of as cast Mg–Zn–Y–Zr alloys

Abstract

In the present work, the effects of Zn content on the microstructures and mechanical properties of as cast Mg–xZn–5Y–0·6Zr alloys (x?=?2, 5, 8 and 13 wt-%) have been investigated. The results show that the ternary Mg–Zn–Y phase compositions change with Zn/Y ratios induced by the change in Zn content. It is found that the fracture is mainly decided by the characteristics and distribution of second phase rather than the grain size. The influences of these phases, especially the W phase, on the mechanical properties of the alloys have been discussed. Both ultimate tensile strength (UTS) and elongation decrease with the increase in Zn content, while the instance of yield strength (YS) is just the reverse. The W phase is easily cracked because of its brittleness and easy to result in decohesion from the matrix because of the weak atomic bonding, which greatly degrade the UTS and elongation. It can be concluded that the YS closely depends on the grain size, while UTS and elongation closely depend on the volume fraction of eutectic compound (α-Mg+W phase).     

Microstructures and mechanical properties of Mg–Zn–Zr–Dy wrought magnesium alloys

Microstructures and phase compositions of as-cast and extruded ZK60–xDy (x?= 0–5) alloys were analysed by optical microscope, scanning electron microscope, X-ray diffraction and differential scanning calorimetry. Meanwhile, the tensile mechanical property was tested. With increasing Dy content, Mg–Zn–Dy new phase increases gradually, while MgZn₂ phase decreases gradually to disappear. As-cast microstructure is refined gradually; meanwhile extruded one is refined further with decreasing average grain size to 1 μm for ZK60–4·32Dy alloy. Second phase, tending to distribute along grain boundary by continuous network in as-cast state, breaks and distributes dispersedly in extrusion state. As-cast tensile mechanical property remains almost unchanged at ambient temperature; however, extruded ones are enhanced significantly at ambient and elevated temperatures, respectively. Tensile strength at 298 and 473 K increases gradually from 355 and 120 MPa for ZK60 alloy to 395 and 171 MPa for ZK60–4·32Dy alloy, respectively. Extruded tensile fractures exhibit a typical character of ductile fracture.     

High cycle fatigue properties of cast Mg–xNd–0.2Zn–Zr alloys

The tensile and fatigue strength of cast Mg–xNd–0.2Zn–0.45Zr alloys (x = 0, 1, 2, 3 wt%) in both solution-treated (T4) and solution + 200 °C peak-aged (T6-PA) conditions were investigated in the present study. The results indicate that Neodymium (Nd) is an effective element to improve both the tensile and fatigue properties of cast Mg–0.2Zn–Zr alloys. The strengthening effect depends on its content in a way of power function (σ = σ₀ + K C _Nd ⁿ ), where the power exponent n is about 0.52–0.54 for yield strength (YS) and 0.59–0.61 for fatigue strength. The yield strengthening effect of Nd element in the form of precipitates (T6-PA) is about three times of that as solution atoms (T4), while the fatigue strengthening effect of Nd element in the form of precipitates is only about 50 % higher than that as solution atoms. The improved strength (both YS and ultimate tensile strength) can lead to the same amount improvement of the fatigue strength in T4-treated alloys, while only can cause less than half improvement of the fatigue strength in T6-PA-treated alloys.