Effects of Zn on microstructure,mechanical properties and corrosion behavior of Mg–Zn alloys

In this study, binary Mg–Zn alloys were fabricated with high-purity raw materials and by a clean melting process. The effects of Zn on the microstructure, mechanical property and corrosion behavior of the as-cast Mg–Zn alloys were studied using direct observations, tensile testing, immersion tests and electrochemical evaluations. Results indicate that the microstructure of Mg–Zn alloys typically consists of primary α-Mg matrix and MgZn intermetallic phase mainly distributed along grain boundary. The improvement in mechanical performances for Mg–Zn alloys with Zn content until 5% of weight is corresponding to fine grain strengthening, solid solution strengthening and second phase strengthening. Polarization test has shown the beneficial effect of Zn element on the formation of a protective film on the surface of alloys. Mg–5Zn alloy exhibits the best anti-corrosion property. However, further increase of Zn content until 7% of weight deteriorates the corrosion rate which is driven by galvanic couple effect.     

Influence of solutionising and aging temperatures on microstructure and mechanical properties of cast Al–Si–Cu alloy

Abstract

This paper presents the influence of solution and aging temperatures on the microstructure and mechanical properties of 319 secondary cast aluminium alloy. Experimental alloy was subjected to different heat treatment cycles. Heat treatments were designed with two solutionising temperatures (504 and 545°C) at two solutionising times (4 and 8 h), followed by quenching in water at 60°C and artificial aging. The artificial aging was carried out at two temperatures (200 and 154°C) for 6 h. The improvement in mechanical properties was obtained with low solution temperature (504°C) for 8 h followed by quenching in water to 60°C and aging at low temperature (154°C). The increase in the solutionising temperature from 504 to 545°C was recommendable only for short solutionising time (4 h). Increase in the aging temperature from 154 to 200°C has led to the increase in hardness with the corresponding decrease in ductility. Aging under unfavourable conditions (prolonged aging at high temperature) caused coarsening of spheroidised eutectic silicon crystals and precipitated particles resulted in deleterious effect on the tensile strength.     

Influence of oxygen content on microstructure and mechanical properties of Ti–Nb–Ta–Zr alloy

The influence of oxygen content on microstructure and mechanical properties of Ti–22.5Nb–0.7Ta–2Zr (at.%) alloy was investigated in this work. According to experiments, the grains were refined apparently when the oxygen content was between 1.5% and 2.0%. The ultimate tensile strength (UTS) increased and elongation decreased with increasing oxygen content. But at the content of 1.0%, the elongation was nearly the same to that of the original alloy (about 16%). The elastic modulus remained comparatively low (<65 GPa) when the content was lower than 1.5%, and then increased dramatically. Therefore, there existed the best oxygen content-1.0%, at which fine grains were obtained, as well as UTS of 750 MPa, elongation of 16% and elastic modulus of 65 GPa. The Ti–22.5Nb–0.7Ta–2Zr–1.0O alloy maintained typical ductile fracture characteristics of beta titanium alloy, and had a little superelasticity.     

Influence of Sc and Zr additions on microstructure and properties evolution of Al–Zn–Mg alloy

Journal of Materials Science - In this study, the effects of different Sc?+?Zr compound addition on the tensile properties, impact toughness, stress corrosion cracking (SCC) properties,...     

Effect of sintering temperature on electrical properties, dielectric characteristics, and aging behavior of ZnO–V2O5-based varistor ceramics modified with Bi2O3

The effect of sintering temperature on microstructure, electrical properties, dielectric characteristics, and aging behavior of ZnO–V₂O₅–MnO₂–Nb₂O₅–Bi₂O₃ varistor ceramics was systematically investigated at 875–950 °C. The sintered density decreased from 5.50 to 5.34 g/cm³ and the average grain size increased from 5.4 to 15.0 μm with an increase in the sintering temperature. The breakdown field (E_B) decreased from 5,785 to 1,181 V/cm with an increase in the sintering temperature. The varistor ceramics sintered at 900 °C exhibited a surprisingly high nonlinear coefficient (α = 61). The donor concentration (N_d) increased from 2.08 × 10¹⁷ to 4.64 × 10¹⁷ cm^?3 with an increase in the sintering temperature and the barrier height (Φ_b) exhibited 1.08 eV as the maximum value at 900 °C. Concerning stability, the varistors sintered at 950 °C exhibited the strongest accelerated aging characteristics, where %ΔE_B = ?1.4 % and %Δα = ?14.6 % for DC accelerated aging stress of 0.85 E_B/85 °C/24 h.     

DC accelerated aging behavior of Co–Dy–Nb doped Zn–V–M-based varistors with sintering process

The DC accelerated aging behavior of the Co–Dy–Nb doped Zn–V–Mn-based varistors was investigated at different sintering temperatures of 850–950 °C. The microstructure of the samples consisted of ZnO grain as the main phase, and Zn₃(VO₄)₂, ZnV₂O₄, and DyVO₄ as the secondary phases, which acts as liquid-phase sintering aids. The nonlinear coefficient exhibited the highest value, reaching 57 for a sintering temperature of 950 °C and the lowest value, reaching 8 for a sintering temperature of 850 °C. Concerning stability, the varistors sintered at lower temperature than 925 °C exhibited a relatively low stability with %ΔE_{1 mA} more than 10%. However, the varistors sintered at higher temperature than 925 °C exhibited a high stability. The varistors sintered at 925 °C exhibited the most stable accelerated aging characteristics, with %ΔE_{1 mA} = −3.9%, %Δα = −40.3%, %Δε_APP′ = −1.0%, and %Δtanδ = +19.1% for DC accelerated aging stress of 0.85 E_{1 mA}/85 °C/24 h.     

Effects of yttrium and zinc addition on the microstructure and mechanical properties of Mg–Y–Zn alloys

The effects of the yttrium and zinc additions on microstructure and mechanical properties of Mg–Y–Zn alloys were investigated. It was found that the addition of yttrium increases the eutectic temperature of Mg–Y–Zn alloys greatly. The addition of yttrium can also greatly increase the dynamic recrystallization (DRX) temperature of Mg–Y–Zn alloys. The volume fraction of DRX grains in Mg₉₇Y₂Zn₁ alloy is larger than that in Mg₉₆Y₃Zn₁ alloy but smaller than that in Mg_95.5Y₃Zn_1.5 alloy due to the effects of yttrium and zinc addition. The long period stacking (LPS) structures of 18R and 14H were observed in Mg–Y–Zn alloys. The increase in the yttrium content results in increase in strength and decrease in elongation in Mg–Y–Zn alloys. The increase in both yttrium and zinc contents results in increase in both strength and elongation in Mg–Y–Zn alloys. The high strengths of the alloys were thought due to the strengthening by the grain refinement, solid solution strengthening, strain strengthening, high density of plane faults of the LPS structures, and distribution of fine Mg₂₄Y₅ phase.     

Influence of sulphur on the microstructure and properties of Ag–Cu–Zn brazing filler metal

Abstract

The effect of sulphur on the microstructure and properties of Ag45–Cu30–Zn25 brazing filler metal was investigated. Under the given experimental conditions, the sulphuration products mainly consisted of CuS, ZnS, Ag₂S, Cu₂S and Ag₃CuS₂. These sulphides not only distributed on the surface but also diffused into the interior of the filler metal and cut apart the matrix thereby significantly damaging the tensile strength of the filler metal from 658 to 283 MPa. The corresponding fracture characterisation turned from ductile fracture to brittle fracture. The sulphides existed as solid particles, which hinder the spreading of the liquid filler metal and the spreading area dramatically decreased from 317?09 to 18?55 mm², which indicates that the filler metal rarely wets the base metal.     

Effect of cooling aging on microstructure and mechanical properties of an Al–Zn–Mg–Cu alloy

In the present work, Al–Zn–Mg–Cu alloy was aged by non-isothermal cooling aging treatment (CAT). At high initial aging temperature (IAT), the hardness was decreased with the decreased cooling rate. However, when IAT was lower than 180 °C, the hardness was increased with the decreased cooling rate. Conductivity was increased with the decreased cooling rate regardless of IAT. The tensile strength, yield strength and conductivity of Al alloy after (200–100 °C, 80 °C/h) CAT were increased 2.9%, 8.1% and 8.3% than that after T6 treatment, respectively. With an increase of IAT and decrease of cooling rate, the fine GP zone and η′ phase were transformed to be larger η′ and η precipitates. Moreover, continuous η phase at grain boundary was also grown to be individual large precipitates. Cooling aging time was decreased about 90% than that for T6 treatment, indicating cooling aging could improve the mechanical properties, corrosion resistance and production efficiency with less energy consumption.     

Effects of trace Er addition on the microstructure and mechanical properties of Mg–Zn–Zr alloy

The effects of trace Er addition on the microstructure in Mg–9Zn–0.6Zr alloy during casting, homogenization, pre-heating, and hot extrusion processes were examined. The mechanical properties of alloys with and without Er were compared. The results showed that Er exhibited a lower solubility in solid magnesium and formed thermally stable Er- and Zn-bearing compounds. The Er-bearing alloy exhibited a considerably improved deformability, as well as a fine and uniform microstructure. Moreover, dynamic precipitation of fine MgZn₂ particles with a modified spherical morphology occurred during hot extrusion, resulting in a tensile yield strength of 313 MPa and a high elongation to failure value of 22%. Further aging of the Er-bearing alloy led to an increment of another 30 MPa in yield strength. In addition, Er markedly increased the thermal stability of the alloy structure.     

Synthesis, structural, electrical and dielectric properties of Zn–Zr doped strontium hexaferrite nanoparticles

Zinc-Zirconium doped Strontium hexaferrite SrZn_xZr_xFe_12?2xO₁₉ (where x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) have been successfully synthesized via sol–gel auto combustion technique. The as-synthesized samples were characterized by thermo gravimetric analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The X-ray powder diffraction results showed that the sample was single phase with the space group of P6₃/mmc. The lattice constant ‘a’ almost remains constant while ‘c’ increases as Zn–Zr concentration ‘x’ increases. The crystallite size obtained from XRD data is in the range of 36–47 nm. The average grain size as determined by SEM was found in the range of 40–90 nm. EDS analysis showed that the composition obtained is near stoichiometric. D.C. electrical resistivity measurements were carried out within the temperature range of 300–923 K. It is observed that the resistivity decreases whereas the drift mobility increases as Zn–Zr content ‘x’ increases. The activation energy is found to decrease with the concentration ‘x’. Dielectric measurements were carried out within the frequency range of 50 Hz–5 MHz. It is found that dielectric constant (ε′) and dielectric loss tangent (tan δ) both increases as the Zn–Zr concentration ‘x’ increases. Moreover, the structural, morphological, electrical and dielectric properties of Sr–M ferrite powders were strongly depend upon the synthesis condition.     

Influence of surface modified TiO2 nanoparticles on dielectric properties of PVdF–HFP nanocomposites

Polyvinylidene fluoride-co-hexaflouropropylene (PVdF–HFP)/TiO₂ hybrid nanocomposites membranes for electrical applications have been prepared using a solvent casting technique. The interface between PVdF–HFP and TiO₂ was modified using aminopropyltrimethoxysilane (APS) coupling agent. The silane linkages on the TiO₂ surface have been confirmed using Fourier transform infra red spectroscopy. WAXD and DSC analysis has been employed to estimate the variation in crystallinity within the membrane as a function of the incorporation of both untreated and APS treated TiO₂. The dispersion of both nanoparticles in the PVdF–HFP matrix were characterized by atomic force microscopy and differences were observed in the images of APS treated and untreated. Variation in electrical properties such as conductivity, dielectric constant, dielectric loss and electric modulus of the hybrid composite films were studied employing AC impedance spectroscopy over a range of frequency from 1 kHz to 1 MHz at room temperature. Theoretical models like Maxwell, Faruka, Rayleigh and Lichtenecker were employed to calculate the effective dielectric constant of hybrid nanocomposite membranes and the estimated values were compared with the experimental data. Further, the variation in thermal stability of PVdF–HFP membrane as a function of untreated and silane treated TiO₂ reinforcement has been estimated using thermogravimetric analysis.     

Influence of aging temperature on corrosion behavior of Al–Zn–Mg–Sc–Zr alloy

Al–Zn–Mg–Sc–Zr alloy sheets were prepared using water chilling copper mould ingot metallurgy processing which was protected by active flux. The effect of aging temperature on the corrosion characteristics of Al–Zn–Mg–Sc–Zr alloy was investigated by means of exfoliation corrosion testing, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) combined with transmission electron microscopy, scanning electron microscopy and optical microscopy observation. It is found that with increasing the aging temperature the susceptibility to exfoliation corrosion decreases. Electrochemical measurements reveal that at early stage of immersion in testing solution, EIS plots of the samples are composed of a capacitive arc and an inductive loop. Inductive loop disappears with the increasing of immersion time and two time constants in impedance diagrams appear. Moreover, the trends of corrosion resistance are further confirmed by polarization curve and EIS test. In addition, transmission electron microscopy observations show that the improved corrosion resistance from increasing aging temperature is duo to the coarsening of matrix and separated precipitates at the grain boundary, and the increased spacing of grain boundary precipitates.     

Influence of the combined addition of Y and Nd on the microstructure and mechanical properties of Mg–Li alloy

Y and Nd are simultaneously added into Mg–5Li–3Al–2Zn alloy. It is found that there exist the phases of α-Mg, AlLi, Al₁₁Nd₃ and Al₂Y in the alloys. When the contents of Y and Nd are 1.2% and 0.8%, respectively, the grain is the finest with an average size of 30 μm, and the tensile strength of the alloy reaches 231 MPa, the elongation reaches 16%. When the ratio of Y to Nd is 1.2:0.8, there is a synergistic strengthening effect.     

Effect of Sr on microstructure,tensile properties and wear behavior of as-cast Mg–6Zn–4Si alloy

The microstructure, tensile properties and wear behavior of as-cast Mg–6Zn–4Si alloy with strontium additions at ambient and elevated temperature were investigated by means of X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), standard high temperature tensile testing and a pin-on-disc type apparatus. The results indicated that the grain size of the primary Mg₂Si decreased initially and then gradually increased with increasing Sr amount. Meanwhile, the morphology of the primary Mg₂Si in the alloys changed from large dendritic to polygonal or fine block, and that of the eutectic Mg₂Si phase turned to fine fibre with increasing Sr content. Tensile testing results showed that Sr addition improved the ultimate tensile and elongation of the Mg–6Zn–4Si alloys at both ambient temperature and 150 °C. Dry sliding wear tests indicated that the change trend of wear rate was basically coincident with that about the average size of the primary Mg₂Si phases. Optimal mechanical properties and wear behavior could be achieved by a Sr addition of 0.5%. An excessive Sr addition resulted in the formation of the needle-like SrMgSi compound, which was detrimental to the tensile properties and wear behavior of the alloys.     

Effect of sintering parameters on microstructure,mechanical properties and electrochemical behavior of Nb–Zr alloy for biomedical applications

Despite the importance of Nb–Zr alloys as candidate materials for biomedical applications, little attention has been given to their processing and the development of new or improved structures. Here, we explore the viability of synthesizing a nano/sub-micron grain structured Nb–Zr alloy through the use of mechanical alloying (MA) and spark-plasma sintering (SPS). The sintered samples were characterized through measurements of densification, Vickers hardness (HV), X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The effect of the SPS parameters on the microstructure and mechanical properties of the sintered alloys was also investigated. Moreover, electrochemical corrosion analyses were performed by a means of a conventional three-electrode cell to assess the corrosion resistance of the developed alloys in Simulated Body Fluids (SBF) medium. A nano/sub-micron grain structured Nb–Zr alloy with an average grain size of between 100 and 300 nm was produced using the MA-SPS techniques. A maximum hardness and relative density of 584 HV and 97.9% were achieved, respectively. Moreover, the nano/sub-micron grain structured Nb–Zr alloy exhibited higher corrosion resistance in SBF medium, which makes this alloy is a promising candidate for use in biomedical applications.     

Magnetic and dielectric properties of Co–Zn ferrite

Nanocrystalline powders of Co substituted Zn ferrite with the chemical formula Co_xZn_1−xFe₂O₄ (x = 0, 0.2, 0.4, 0.6, 0.8, 1) were synthesized by sol–gel autocombustion method using tartaric acid as fuel agent. The samples were sintered in static air atmosphere for 7 h at 773 K, 7 h at 973 K and 10 h at 1173 K. The organic phase extinction and the spinel phase formation were monitored by means of Fourier transform infrared spectroscopy. The X-ray diffraction patterns analysis confirmed the spinel single phase accomplishment. Crystallite size, average grains size, lattice parameter and cation distribution were estimated. Magnetic behavior of the as-obtained samples by means of M-H hysteresis measurements was studied at room temperature. Permeability and dielectric permittivity at room temperature versus frequency was the subject of a comparative study for the Co_xZn_1−xFe₂O₄ series. In agreement with the proposed cation distribution the sample with Co_0.8Zn_0.2Fe₂O₄ formula exhibits the optimal magnetic and dielectric properties.