Superplastic behavior of a fine-grained ZK60 magnesium alloy processed by high-ratio differential speed rolling

Grain size of the ZK60 alloy was effectively reduced to 12 μm through high-ratio differential speed rolling (HRDSR) for a thickness reduction of 70% in a single pass. Due to the strengthening effects of grain boundaries and particles, the HRDSR processed ZK60 exhibited a high tensile strength of 340 MPa. Low temperature superplasticity was attained at 473–493 K at low strain rates (5 × 10⁻⁴ s⁻¹) and high strain rate superplasticity was attained at 523–553 K at high strain rates (10⁻² s⁻¹). The optimum superplastic temperature was found to be 553 K where a maximum tensile elongation of 1000% was obtained at 1 × 10⁻³ s⁻¹. The deformation behavior of the HRDSR processed ZK60 at elevated temperatures could be depicted by considering contribution of grain boundary sliding and slip creep to total plastic flow. Difference in superplastic deformation behavior between the HRDSR processed and equal channel angular press processed ZK60 alloys was examined and discussed.     

Structure and mechanical properties of extruded Mg–Gd based alloy sheet

The Mg–8Gd–2Y–1Nd–0.3Zn–0.6Zr (wt.%) alloy sheet was prepared by hot extrusion technique, and the structure and mechanical properties of the extruded alloy were investigated. The results show that the alloy in different states is mainly composed of α-Mg solid solution and secondary phases of Mg₅RE and Mg₂₄RE₅ (RE = Gd, Y and Nd). At aging temperatures from 200 °C to 300 °C the alloy exhibits obvious age-hardening response. Great improvement of mechanical properties is observed in the peak-aged state alloy (aged at 200 °C for 60 h), the ultimate tensile strength (σ_b), tensile yield strength (σ_0.2) and elongation () are 376 MPa, 270 MPa and 14.2% at room temperature (RT), and 206 MPa, 153 MPa and 25.4% at 300 °C, respectively, the alloy exhibits high thermal stability.     

Effect of Zr addition on the microstructure and properties of Cu–10Cr in situ composites

The Cu–10Cr–0.4Zr alloy and the in situ composites based on the alloy were prepared. Microstructure evolution and mechanical properties of Cu–10Cr–0.4Zr in situ composites were investigated. The results showed that the addition of 0.4 wt.% Zr in the Cu–10 wt.% Cr in situ composites gave birth to smaller as-cast Cr dendrites, which led to finer filaments at higher strain ratios. The ultimate strength of Cu–10Cr–0.4Zr composites reached 1089 MPa at draw ratio of η = 6.2, however that of Cu–10Cr prepared by the same procedure was only 887 MPa. The increasing strength of Cu–10Cr–0.4Zr in situ composites could be attributed to the combination of Hall–Petch strengthening of closely spaced Cr filaments, the strengthening effect of Zr and the strengthened Cu matrix.     

Low-temperature compaction of Ti–6Al–4V powder using equal channel angular extrusion with back pressure

Equal channel angular extrusion (ECAE), with simultaneous application of back pressure, has been applied to the consolidation of 10 mm diameter billets of pre-alloyed, hydride–dehydride Ti–6Al–4V powder at temperatures ≤400 °C. The upper limit to processing temperature was chosen to minimise the potential for contamination with gaseous constituents potentially harmful to properties of consolidated product. It has been demonstrated that the application of ECAE with imposed hydrostatic pressure permits consolidation to in excess of 96% relative density at temperatures in the range 100–400 °C, and in excess of 98% at 400 °C with applied back pressure ≥175 MPa. ECAE compaction at 20 °C (back pressure = 262 MPa) produced billet with 95.6% relative density, but minimal green strength. At an extrusion temperature of 400 °C, the relative density increased to 98.3%, for similar processing conditions, and the green strength increased to a maximum 750 MPa. The relative density of compacts produced at 400 °C increased from 96.8 to 98.6% with increase in applied back pressure from 20 to 480 MPa, while Vickers hardness increased from 360 to 412 HV. The key to the effective low-temperature compaction achieved is the severe shear deformation experienced during ECAE, combined with the superimposed hydrostatic pressure.     

Effect of rapid solidification on the microstructure and mechanical properties of hot-pressed Al–20Si–5Fe alloys

The aim of this work is to study the effect of cooling rate and subsequent hot consolidation on the microstructural features and mechanical strength of Al–20Si–5Fe–2X (X = Cu, Ni and Cr) alloys. Powder and ribbons were produced by gas atomization and melt spinning processes at two different cooling rates of 1 × 10⁵ K/s and 5 × 10⁷ K/s. The microstructure of the products was examined using optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The particles were consolidated by hot pressing at 400 °C/250 MPa/1 h under a high purity argon atmosphere and the microstructure, hardness and compressive strength of the compacts were evaluated. Results showed a profound effect of the cooling rate, consolidation stage, and transition metals on the microstructure and mechanical strength of Al–20Si–5Fe alloys. While microstructural refining was obtained at both cooling rates, the microstructure of the atomized powder exhibited the formation of fine primary silicon (~ 1 μm), eutectic Al–Si phase with eutectic spacing of ~ 300 nm, and δ-iron intermetallic. Supersaturated Al matrix containing 5–7 at.% silicon and nanometric Si precipitates (20–40 nm) were determined in the microstructure of the melt-spun ribbons. The hot consolidation resulted in coarsening of Si particles in the atomized particles, and precipitation of Si and Fe-containing intermetallics from the supersaturated Al matrix in the ribbons. The consolidated ribbons exhibited higher mechanical strength compared to the atomized powders, particularly at elevated temperatures. The positive influence of the transition metals on the thermal stability of the Al–20Si–5Fe alloy was noticed, particularly in the Ni-containing alloy.     

Creep behavior of Mg–2 wt.%Nd binary alloy

A binary magnesium alloy, Mg–2 wt.%Nd, has been prepared. Under the condition of temperature between 150 and 250 °C and applied stress between 30 and 110 MPa, the alloy exhibits good creep resistance due to both solution-hardening and especially precipitation-hardening. Tiny precipitates forming dynamically during creep have been observed, which play an important role in restricting dislocation movements. When the creep tests are carried out at the temperature range between 150 and 250 °C, the stress exponents lie in the range of 4.5–7.1 at low stresses, which is consistent with the “five-power-law”. The values of stress exponent increase up to 9.8–29.5 at high stresses indicate power-law breakdown. When the creep tests are carried out under the applied stress between 30 and 90 MPa, the apparent activation energy values vary from 70.0 to 96.0 kJ/mol at low temperatures, but increase to 199.9–246.1 kJ/mol at high temperature range. Dislocations in basal plane are activated in the primary creep stage, but as creep goes on, they are observed in non-basal plane. The creep is mainly controlled by both dislocation-climb and cross-slip.     

Synthesis and properties of bulk metallic glasses in the ternary Ni–Nb–Zr alloy system

Bulk metallic glasses (BMGs) with high thermal stability, good mechanical properties and high corrosion resistance were synthesized in the Ni–Nb–Zr system. A large bulk glass-forming region with 60 < Ni < 64, 28 < Nb < 38 and 0 < Zr < 9 (in at.%) was found. The critical size for the glass formation is 3 mm. These investigated Ni-based BMGs process high glass transition temperature of about 880–900 K and high on-set crystallization temperature of 915–932 K as well as high compressive fracture strength of approximate 3.0–3.2 GPa along with some compressive plasticity of about 2%. Electrochemical measurements indicate they also exhibit high corrosion resistance, i.e., large passive region above 1.5 V (vs. saturated calomel reference electrode, SCE). The influence of the Zr content on the glass-forming ability (GFA) and corrosion behaviors was carefully studied, indicating that some Zr addition improves the GFA and corrosion resistance.     

Oxidation resistance of dense carbon fiber/Si–O–C glass composite fabricated by pre-oxidation and spark plasma sintering

The carbon fiber/Si–O–C glass composite was prepared from the silicone and carbon fiber by pre-oxidation and spark plasma sintering (sintered composite). The mass loss of the sintered composite oxidized at 1200 °C for 90 min was 5%, which was lower than that of same dimension for similar composites, although the mass loss at 600 °C was still high. This indicated its excellent oxidation resistance at elevated temperature. No cracks and pores were found in the sintered composite, indicating that the combination of pre-oxidation and spark plasma sintering was better than the pyrolysis for manufacturing dense composites. Compared with the flexural strength of about 60 MPa for carbonaceous composites, the flexural strength of the sintered composite was obviously improved to 220 MPa. Moreover, microstructures of the specimen before and after sintering as well as after oxidation were investigated.     

Forging of Mg–3Al–1Zn–1Ca alloy prepared by high-frequency electromagnetic casting

The 1 wt.%Ca–AZ31 alloy produced by electromagnetic casting (EMC) in presence of electromagnetic stirring (EMS) was extruded and then subjected to the closed-die forging to make a pulley for automobile application. Effective dynamic recrystallization (DRX) took place during the forging process, leading to formation of fully recrystallized grains with the average size of 3–4 μm. High-forging ability and high degree of grain refinement achieved during the forging were attributed to the novel microstructure of the cast composed of small and equiaxed grains with the average size of 50 μm and thin layer (Al, Mg)₂ Ca phase at grain boundaries, which would provide more nucleation sites and a faster rate of recrystallization during deformation by forging as compared to that of the conventionally processed cast composed of large size grains and thick layer (Al, Mg)₂ Ca phase. The forged pulley exhibited the ultimate tensile strength of 273–286 MPa with tensile elongations of 30%. The present result demonstrates a possibility that EMC + EMS techniques can be used in producing magnesium feed stocks with high-forging ability.     

Effects of Al–5Ti–1B and Al–5Zr master alloys on the structure, hardness and tensile properties of a highly alloyed aluminum alloy

This study was undertaken to investigate the influence of Al–5Ti–1B and Al–5Zr master alloys on the structural characteristics and tensile properties of Al–12Zn–3 Mg–2.5Cu aluminum alloy. The optimum amount for Ti and Zr containing master alloys was selected as 1 wt.% and 6 wt.%, respectively. The results also showed that Ti containing master alloy is more effective in reducing average grain size of the alloy. T6 heat treatment was applied for all specimens before tensile testing. In heat treated condition, the average tensile strength of 505 MPa was found to be increased to 621 MPa for sample refined with 1 wt.% Al–5Ti–1B (0.05 wt.% Ti). SEM fractography of the fractured faces of several castings showed an overall macroscopically brittle appearance at low magnifications. At higher magnifications, unrefined specimens showed cracking along the grains, whereas Ti-refined specimens showed cracks in individual intermetallic compounds.     

Properties of Ti–6Al–4V non-stochastic lattice structures fabricated via electron beam melting

This paper addresses foams which are known as non-stochastic foams, lattice structures, or repeating open cell structure foams. The paper reports on preliminary research involving the design and fabrication of non-stochastic Ti–6Al–4V alloy structures using the electron beam melting (EBM) process. Non-stochastic structures of different cell sizes and densities were investigated. The structures were tested in compression and bending, and the results were compared to results from finite element analysis simulations. It was shown that the build angle and the build orientation affect the properties of the lattice structures. The average compressive strength of the lattice structures with a 10% relative density was 10 MPa, the flexural modulus was 200 MPa and the strength to density ration was 17. All the specimens were fabricated on the EBM A2 machine using a melt speed of 180 mm/s and a beam current of 2 mA. Future applications and FEA modeling were discussed in the paper.     

Effect of initial temper on the creep behavior of a Mg–Gd–Nd–Zr alloy

The effect of initial temper on the tensile creep behavior of a cast Mg–Gd–Nd–Zr alloy has been investigated. Specimens in unaged, underaged and peak-aged conditions exhibit a sigmoidal creep stage between the primary and steady-state creep stage, while the overaged specimens have no such creep stage. Transmission electron microscope observations revealed that sigmoidal creep stage was induced by the dynamic precipitation in the microstructure, and the rapid formation of β₁-phase and β-phase plates takes responsibility for the softening of material in this stage. Comparative evaluation of creep properties of the specimens showed that alloy in overaged condition had creep resistance superior to those in other conditions. Stress and temperature dependence of the steady-state creep rate were studied over a temperature range of 250–300 °C and stress range of 50–100 MPa, and a dislocation creep mechanism was proposed for the alloy.     

Joining of zirconia to metal with Cu–Ga–Ti and Cu–Sn–Pb–Ti fillers

The method of brazing by capillary impregnation of Cu–Ga melt through a titanium powder layer situated between brazed details is elaborated. Samples of ZrO₂ ceramic/metal brazed joints using Cu–Ga–Ti filler and Cu–Sn–Pb–Ti filler were fabricated. The joints’ shear strength was 277±37 MPa for the Cu–Ga–Ti and 156±25 MPa for the Cu–Sn–Pb–Ti.     

Preparation of C200 green reactive powder concrete and its static–dynamic behaviors

In this paper, a new type of green reactive powder concrete (GRPC) with compressive strength of 200 MPa (C200 GRPC) is prepared by utilizing composite mineral admixtures, natural fine aggregates, short and fine steel fibers. The quasi-static mechanical properties (mechanical strength, fracture energy and fiber–matrix interfacial bonding strength) of GRPC specimens, cured in three different types of regimes (standard curing, steam curing and autoclave curing), are investigated. The experimental results show that the mechanical properties of the C200 GRPC made with the cementitious materials consisting of 40% of Portland cement, 25% of ultra fine slag, 25% of ultra fine fly ash and 10% of silica fume, 4% volume fraction of steel fiber are higher than the others. The corresponding compressive strength, flexural strength, fracture energy and fiber–matrix interfacial bonding strength are more than 200 MPa, 60 MPa, 30,000 J/m² and 14 MPa, respectively. The dynamic tensile behavior of the C200 GRPC is also investigated through the Split Hopkinson Pressure Bar (SHPB) according to the spalling phenomena. The dynamic testing results demonstrate that strain rate has an important effect on the dynamic tensile behavior of C200 GRPC. With an increase of strain rate, the peak stress rapidly increases in the dynamic tensile stress–time curves. The C200 GRPC exhibits an obvious strain rate stiffening effect in the case of high strain rate. Finally, the mechanism of excellent static and dynamic properties gains of C200 GRPC is also discussed.     

Influence of additives on the microstructure and tensile properties of near-eutectic Al–10.8%Si cast alloy

The continuing quest for aluminum castings with enhanced mechanical properties for applications in the automotive industries has intensified the interest in aluminum–silicon alloys. In Al–Si alloys, the properties are influenced by the shape and distribution of the eutectic silicon particles in the matrix, as also by the iron intermetallics and copper phases that occur upon solidification. The detailed microstructure and tensile properties of as-cast and heat-treated new experimental alloy belonging to cast Al–Si near-eutectic alloys have been investigated as a function of Fe, Mn, Cu, and Mg content. Microstructural examination was carried out using optical microscopy, image analysis, and electron probe microanalysis (EPMA), wavelength dispersive spectroscopic (WDS) analysis facilities. Tensile properties upon artificial aging in the temperature range of 155–240 °C for 5 h were also investigated. The results show that the volume fraction of Fe-intermetallics increases as the iron or manganese contents increase. Compact polygonal or star-like particles form when the sludge factor is greater than 2.1. The Al₂Cu phase was observed to dissolve almost completely during solution heat treatment of all the alloys studied, especially those containing high levels of Mg and Fe, while Al₅Cu₂Mg₈Si₆, sludge, and α-Fe phases were found to persist after solution heat treatment. The β-Al₅(Fe,Mn)Si phase dissolved partially in Sr-modified alloys, and its dissolution became more pronounced after solution heat treatment. At 0.5% Mn, the β-Fe phase forms when the Fe content is above 0.75%, causing the tensile properties to decrease drastically. The same results are obtained when the levels of both Fe and Mn are increased beyond 0.75%, because of sludge formation. On the other hand, the tensile properties of the Cu-containing alloys are affected slightly at high levels of Mg as a result of the formation of Al₅Cu₂Mg₈Si₆ which decreases the amount of free Mg available to form the Al₂CuMg phase. The results also show that, for the heat-treated alloys, peak aging is achieved at 180 °C, although the highest quality index corresponds to 155 °C aging temperature, for all the alloys investigated. Accordingly, 155 °C may be considered as the optimal aging treatment. It is also consistent with this observation that quality index is more sensitive to variations in tensile ductility than in tensile strength.     

Microstructure and mechanical properties of Al–20Si–5Fe–2X (X = Cu, Ni, Cr) alloys produced by melt-spinning

Al–20Si–5Fe–2X (X = Cu, Ni and Cr) ribbons were produced by melt-spinning and consolidated by hot pressing at 400 °C for 60 min. The microstructure of the ribbons and the consolidated alloys was investigated using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffractometry (XRD) method, and transmission electron microscopy (TEM). The hardness and compressive strength of the specimens at ambient and elevated temperatures were examined. The microstructure of the ribbons exhibited featureless and dendritic zones. Results of XRD and TEM showed formation of spherically shaped Si particles with an average diameter of 20 nm. Ultrafine Si (110–150 nm) and iron-containing intermetallic particles were noticed in the microstructure of the consolidated ribbons. An improved strength was achieved by alloying of Al–20Si–5Fe with Cu, Ni, and Cr. Nickel was found to be the most effective element in increasing the maximum stress, particularly at elevated temperatures.     

Effects of heat treatments on the microstructures and mechanical properties of Mg–3Nd–0.2Zn–0.4Zr (wt.%) alloy

Microstructure and mechanical properties of as-cast and different heat treated Mg–3Nd–0.2Zn–0.4Zr (wt.%) (NZ30K) alloys were investigated. The as-cast alloy was comprised of magnesium matrix and Mg₁₂Nd eutectic compounds. After solution treatment at 540 °C for 6 h, the eutectic compounds dissolved into the matrix and small Zr-containing particles precipitated at grain interiors. Further aging at low temperatures led to plate-shaped metastable precipitates, which strengthened the alloy. Peak-aged at 200 °C for 10–16 h, fine β″ particles with DO₁₉ structure was the dominant strengthening phase. The alloy had ultimate tensile strength (UTS) and elongation of 300–305 MPa and 11%, respectively. Aged at 250 °C for 10 h, coarse β′ particles with fcc structure was the dominant strengthening phase. The alloy showed UTS and elongation of 265 MPa and 20%, respectively. Yield strengths (YS) of these two aged conditions were in the same level, about 140 MPa. Precipitation strengthening was the largest contributor (about 60%) to the strength in these two aged conditions. The hardness of aged NZ30K alloy seemed to correspond to UTS not YS.     

Optimization and kinetics of electroless Ni–P–B plating of quartz optical fiber

The preparation of Ni–P–B coatings on surface of quartz optical fibers was carried out using electroless plating method. The effects of the concentrations of nickel chloride, sodium hypophosphite, potassium borohydride, ethylenediamine, cadmium sulfate and temperature on the quality of Ni–P–B coatings were investigated by orthogonal experiment and their optimal values were determined to be: 0.1 mol L⁻¹, 0.094 mol L⁻¹, 0.185 mol L⁻¹, 0.36 mol L⁻¹, 5.68 × 10⁻⁴ mol L⁻¹ and 90 °C, respectively. The effect of coarsening time of the naked fiber on the quality of Ni–P–B coatings was also researched and the optimal coarsening time was determined to be 15 min. Stereomicroscope, Scanning Electron Microscope and X-ray diffractometer were used to characterize the apparentness, morphology and structure of the prepared Ni–P–B coatings. Inductively Coupled Plasma-Atomic Emission Spectroscopy, Thermal Shock Method and Gravimetric Analysis Method were employed to analyze the composition, force of adhesion and solderability of the coatings, respectively. The results showed that a Ni–P–B coating with low surface roughness, good strength of adhesion, low resistivity and good solderability was successfully prepared. The kinetic models (Ni–P–B deposition rate equations) of the process were established as . The theoretical values calculated by the models were proved to be basically consistent with the practical measurements through experimental verification.     

A study of tensile properties in Al–Si–Cu and Al–Si–Mg alloys: Effect of β-iron intermetallics and porosity

The effect of β-iron intermetallics and porosity on the tensile properties in cast Al–Si–Cu and Al–Si–Mg alloys were investigated for this research study, using experimental and industrial 319.2 alloys, and industrial A356.2 alloys. The results showed that the alloy ductility and ultimate tensile strength (UTS) were subject to deterioration as a result of an increase in the size of β-iron intermetallics, most noticeable up to β-iron intermetallic lengths of 100 μm in 319.2 alloys, or 70 μm in A356.2 alloys. An increase in the size of the porosity was also deleterious to alloy ductility and UTS. Although tensile properties are interpreted by means of UTS vs. log elongation plots in the present study, the properties for all sample conditions were best interpreted by means of log UTS vs. log elongation plots, where the properties increased linearly between conditions of low cooling rate–high Fe and high cooling rate–low Fe. The results are explained in terms of the β-Al₅FeSi platelet size and porosity values obtained.     

Effect of prior cold work on age hardening of Cu–3Ti–1Cr alloy

The influence of 50%, 75% and 90% cold work on the age hardening behavior of Cu–3Ti–1Cr alloy has been investigated by hardness and tensile tests, and light optical and transmission electron microscopy. Hardness increased from 118 Hv in the solution-treated condition to 373 Hv after 90% cold work and peak aging. Cold deformation reduced the peak aging time and temperature of the alloy. The yield strength and ultimate tensile strength reached a maximum of 1090 and 1110 MPa, respectively, following 90% deformation and peak aging. The microstructure of the deformed alloy exhibited elongated grains and deformation twins. The maximum strength on peak aging was obtained due to precipitation of the ordered, metastable and coherent β′-Cu₄Ti phase, in addition to high dislocation density and deformation twins. Over-aging resulted in decreases in hardness and strength due to the formation of incoherent and equilibrium β-Cu₃Ti phase in the form of a cellular structure. However, the morphology of the discontinuous precipitation changed to a globular form on high deformation. The mechanical properties of Cu–3Ti–1Cr alloy are superior to those of Cu–2.7Ti, Cu–3Ti–1Cd and the commercial Cu–0.5Be–2.5Co alloys in the cold-worked and peak-aged condition.