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     

The Effect of Sn Substitution of Pb on Microstructure and Superconducting Properties of Bi–Pb–Sr–Ca–Cu–O Superconductor

The effect of substitution of Pb by Sn in Bi_1.6Pb_0.4?x Sn _x Sr₂Ca₂Cu₃ O _δ samples at x = 0.0, 0.1, 0.2, and 0.3 on the critical transition temperature and structural properties was investigated in this work. All the samples were prepared by the solid-state reaction method. The prepared samples were characterized by X-ray diffraction (XRD), resistance–temperature curve (R–T), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The Sn ⁴⁺ substitution of Pb ²⁺ caused significant changes in the properties of the samples. The formation of the (Bi, Pb)-2212 phase was stabilized and the T _c (onset) was improved at the x = 0.2 level of Sn ⁴⁺ substitution. The SEM micrographs have shown that the structure of the sample with x = 0.2 became more dense. However, samples with x = 0.1 and 0.3 have not shown zero resistance by EDS analysis because of oxygen deficiency.     

Application of time–temperature–stress superposition on creep of wood–plastic composites

Time–temperature–stress superposition principle (TTSSP) was widely applied in studies of viscoelastic properties of materials. It involves shifting curves at various conditions to construct master curves. To extend the application of this principle, a temperature–stress hybrid shift factor and a modified Williams–Landel–Ferry (WLF) equation that incorporated variables of stress and temperature for the shift factor fitting were studied. A wood–plastic composite (WPC) was selected as the test subject to conduct a series of short-term creep tests. The results indicate that the WPC were rheologically simple materials and merely a horizontal shift was needed for the time–temperature superposition, whereas vertical shifting would be needed for time–stress superposition. The shift factor was independent of the stress for horizontal shifts in time–temperature superposition. In addition, the temperature- and stress-shift factors used to construct master curves were well fitted with the WLF equation. Furthermore, the parameters of the modified WLF equation were also successfully calibrated. The application of this method and equation can be extended to curve shifting that involves the effects of both temperature and stress simultaneously.     

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     

Effect of CeLa addition on the mechanical properties of Al–Cu–Mn–Mg–Fe alloy

The rapid development of new energy automobiles leads to an increasing demand for high-strength lithium battery shell alloy. The microstructures, electrical conductivity and mechanical properties of CeLa-containing Al–Cu–Mn–Mg–Fe alloys were investigated with scanning electron microscopy (SEM), X-ray diffraction, Eddy Current conductivity tester, tensile testing and Erichsen cup testing. Experiment results indicate that Al₆(Mn, Fe) particles could be refined by CeLa alloying and AlCuCeLa phase nucleates and grew up at the surface of Al₆(Mn, Fe) particle. Major texture of the CeLa-containing alloys was different from that of the CeLa-free alloy. The electrical conductivity decreased with increase of the CeLa content. CeLa addition could greatly enhance the tensile strength of the alloy at temperatures ranging from –40°C to 300°C.     

Influence of ageing on wear resistance of an Fe–Mn–Si–Cr–Ni–Ti–C shape memory alloy

To further improve the wear resistance of Fe–Mn–Si–Cr–Ni based shape memory alloys, the effects of ageing at 1123 K with and without pre-deformation at room temperature on the precipitation of second-phase particles and their effects on wear resistance were investigated in an Fe–Mn–Si–Cr–Ni–Ti–C alloy. Results showed that the solution treated Fe–Mn–Si–Cr–Ni–Ti–C alloy exhibited much better wear resistance than the solution treated AISI 321 stainless steel; ageing with pre-deformation improved the wear resistance of Fe–Mn–Si–Cr–Ni–Ti–C alloy more effectively than ageing without pre-deformation, especially under the heavy load condition.     

Constitution of Ti–Al–Ru system

Abstract

The constitution of the Ti–Al–Ru system has been studied in detail. Metallography, X-ray diffraction, electron microscopy, and X-ray spectroscopy have been used to establish the phase diagram between 17 and 37 at.-%Al and 1 and 29 at.-%Ru in the temperature range 1250–770°C. Ternary isothermal sections within the range of investigation and selected phase composition data are presented and phase relationships are discussed. Results show only a small solubility (< 1at.-%) of ruthenium in Ti₃Al and TiAl which are involved in equilibria with a ternary intermetallic compound.

MST/963     

Thermodynamic analysis of the formation reaction of second phases in Mg–Zn–Mn–Sn–Nd alloys

The thermodynamic characteristics and solidification sequence of Mg–6Zn–1Mn–4Sn–xNd (x?=?0.5, 1.0, 1.0, wt-%, ZMT614-xNd) alloys were investigated using CALPHAD, Miedema model, differential scanning calorimetry and transmission electron microscopy (TEM) analysis. The results revealed that the as-cast ZMT614-Nd alloys consisted of α-Mg, Mn, Mg₇Zn₃, Mg₂Sn and MgSnNd phases. Owing to its higher phase transition temperature and lower formation enthalpy, MgSnNd phase formed first during the casting process. The formation of MgSnNd phase consumed all Nd elements, which restrained the formation of other Nd-containing phases. As a result, the solidification sequence of ZMT614-1.5Nd alloy was α-Mg?→?MgSnNd?→?Mn?→?Mg₂Sn?→?Mg₇Zn₃. TEM analysis suggested that the MgSnNd phase had a low-symmetry crystal structure.     

Effect of heat treatment on strain–controlled fatigue behavior of cast Mg–Nd–Zn–Zr alloy

The influence of heat treatment on the strain-controlled fatigue behavior of cast NZ30?K alloy was investigated. Compared with the as-cast and solutionized (T4) alloys, the peak-aged (T6) and over-aged (T7) counterparts have a higher cyclic stress and a lower plastic strain value due to the precipitation strengthening. The as-cast and T4-treated alloys have a higher fatigue strength/yield strength ratio than the aged alloys, which is mainly attributed to their higher cyclic hardening. Under stress-controlled loading, the aged alloys show lower hysteresis energies than the as-cast and T4-treated counterparts, leading to longer fatigue lifetimes. For the T4-treated alloy, the cyclic hardening and fatigue failure are controlled by the dislocations-slip and twinning, while for both the as-cast and T6-treated counterparts, they are controlled by the dislocation-slip. For the T7-treated alloy, cyclic deformation and failure behavior are mainly dependent on dislocations-slip and grain boundary sliding.     

Constitution of Ni3Al–Ni3Mo–Ni3W section of Ni–Al–Mo–W system

Abstract

The isothermal section of the Ni–Al–Mo–W system has been studied at 75 at.-%Ni at temperatures of 1523 and 1273 K. Constitutional data have been determined using electron probe microanalysis, X-ray diffraction, and microscopical examination. The alloys studied lay in the range 12·5–15 at.-%Al, 2·5–7·5 at.-%Mo, and 2·5–7·5 at.-% W. The phases present at 1523 K were γ, γ′, and α (based on the Mo–W continuous series of solid solutions); at 1273 K, NiMo(δ′) was also encountered. The γ/γ′ mismatch values lay in the range ?0·03 to ?0·75%. In the as-solidified state, the alloys consisted predominantly of γ-phase containing γ′-precipitates formed in the solid state.

MST/462     

Investigation of quench sensitivity of high strength Al–Zn–Mg–Cu alloys by time–temperature-properties diagrams

The quench sensitivity of some typical high strength Al–Zn–Mg–Cu alloys, including 7075, 7175, 7050, 7010, 7055, 7085 and 1933, was investigated by time–temperature-properties (TTP) diagrams which were from the present paper and literature. The drop in the mechanical properties due to decreased quenching rate was predicted by quench factor analysis method. The nose temperature of TTP diagrams was the highest for 7055 alloy and the lowest for 7085 alloy. The critical time at the nose temperature was the shortest for 7055 alloy and the longest for 1933 alloy. Decreased quenching rate to 10 k/s led to drop in the properties less than 2% for 7085 and 1933 alloys, but more than 20% for 7075, 7175 and 7055 alloy. Thus, 7075, 7175 and 7055 alloys were the most quench sensitive alloys, while 7085 and 1933 alloys were the least quench sensitive ones. The differences in the quench sensitivity of these alloys were explained mainly based on its chemical compositions.     

Characterisation of the bioactive behaviour of sol–gel hydroxyapatite–CaO and hydroxyapatite–CaO–bioactive glass composites

The fabrication and characterization of sol–gel derived hydroxyapatite–calcium oxide (HAp–CaO) material is investigated focusing on the effect of the addition of a bioactive glass on the material bioactive behaviour through the fabrication of a novel HAp–CaO (70 wt.%)–bioactive glass (30 wt.%) composite material. The bioactive behaviour of the materials was assessed by immersion studies in Simulated Body Fluid (SBF) and the alterations of the materials surfaces after soaking periods in SBF were characterized by Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR). A brittle and weakly crystalline carbonate hydroxyapatite (HCAp) layer was found to develop on the surface of all samples, few hours after immersion in SBF, confirming the high bioactivity of the material. Alterations of the morphology of the developed HCAp layer, which led to a more compact structure, were observed on the surface of composite samples after 7 days of immersion in SBF. The presence of the CaO phase seems to accelerate the formation of HCAp, while the bioactive glass affects both the morphology and cohesion of the developed layer.     

Characterization of corrosion phenomena of Zr–Ti–Cu–Al–Ni metallic glass by SEM and TEM

Corrosion phenomena are investigated for a Zr₅₉Ti₃Cu₂₀Al₁₀Ni₈ metallic glass immersed in hydrofluoric acid (HF) in open-circuit conditions and by means of electron microscopies (SEM and TEM). Several morphologies develop on the corroded surface and especially large and deep pits. TEM study demonstrates that Cu-rich nanocrystals of 5–10 nm are formed inside the corrosion pits (on their walls) during the corrosion process. These nanocrystals are not only by-products of the corrosion process but they very likely play a role in the development of the corrosion pitting morphology. They could have a dual role: (i) protecting the capped areas against dissolution and (ii) speeding the dissolution of neighboring uncapped areas by the creation of local galvanic cells.     

Effect of Homogenization Process on Microstructure of Al–Zn–Mg–Cu Aluminum Alloys

Herein, the best homogenization process of 466.5 °C × 36 h + 490 °C × (14–26.4 h) that can completely eliminate the coarse phases σ[Mg(Zn, Al, Cu)₂] and S(Al₂CuMg) in the Al–Zn–Mg–Cu aluminum alloy is developed. The homogenization process is determined by the method of calculation phase diagram, and the experimental verification. It is shown in the results that, first, in the microstructure of the as-cast alloys, the crystal structure of the σ[Mg(Zn, Al, Cu)₂], Al₇Cu₂Fe, and Mg₂Si phases is determined. Second, during the homogenization process, the σ[Mg(Zn, Al, Cu)₂] phase dissolves and also transforms into the S(Al₂CuMg) phase. Most importantly, the dissolution temperature range of the σ[Mg(Zn, Al, Cu)₂], S(Al₂CuMg), and Al₇Cu₂Fe phases is determined from 472.56 to 476.36 °C, from 484.09 to 485.39 °C, and from 540.18 to 547.23 °C, respectively. At best homogenization process, the residual Al₇Cu₂Fe phase area fraction ranges from 1.28 ± 0.16% to 1.60 ± 0.18%. In addition, dispersed η(MgZn₂) phase precipitates in supersaturated Al-matrix during differential scanning calorimeter heating. And, the concentration differences between the grain center and the eutectic of structure of Zn, Mg and Cu regression equations are established, which can provide some reference for the design of experimental parameters, thus reducing the experimental workload.     

Properties of coatings of the Al–Cr–Fe–Co–Ni–Cu–V high entropy alloy produced by the magnetron sputtering

It has been found that coatings from an Al–Fe–Co–Ni–Cu–Cr–V high entropy equiatomic alloy produced by the magnetron sputtering have nanocrystalline microstructures, are textured, and present a solid two-phase solution, which crystallizes in the bcc (a = 2.91 Å) and fcc (a = 3.65 Å) phases. The ion bombardment of a growing coating caused by the bias voltage (0–(–200) V), which has been applied to the substrate, decreases the growth rate of a condensate and affects its composition and structure. It has been shown that the composition of coatings deposited without an ion bombardment coincides with the target composition, whereas an increase of the ion bombardment intensity leads to the depletion of the coating composition in Al, Cu, and Ni and increase the microhardness. The anisotropy of the coating produced has been revealed.     

Effect of deformation on corrosion behavior of Ti–23Nb–0.7Ta–2Zr–O alloy

The influence of deformation on the corrosion behavior of a newly developed multifunctional beta titanium alloy Ti–23Nb–0.7Ta–2Zr–O (mol%) in Ringer's solution at 310 K was evaluated using an electron backscatter diffraction technique and electrochemical measurements. The results showed that the effect of deformation on the corrosion resistance of the beta titanium alloy is complicated. Small levels of plastic deformation are detrimental to the corrosion resistance, whereas large deformations tend to eliminate this detrimental effect.     

Extrusion processing of Al–Li–Mg–Zr alloy

Abstract

The hot deformation behaviour of an Al–Li–Mg–Zr alloy was characterised in hot torsion and extrusion. The alloy was found to have similar hot ductility to existing high strength aluminium alloys, but this could be maintained at higher temperatures. Billets were extruded over a range of process conditions and a limit diagram was constructed for surface cracking. All the extrusions were found to be partially recrystallised after deformation, but the volume fraction of recrystallisation was a strong function of billet temperature and extrusion ratio. In addition, the unrecrystallised areas contained a recovered substructure where the subgrain size was inversely proportional to the temperature compensated strain rate. The as extruded structure was retained during solution treatment and as a result final mechanical properties were strongly dependent on the extrusion conditions. The use of high billet temperatures and low extrusion ratios gave the best combination of strength and toughness.

MST/839     

DSC and TEM characterizations of thermal stability of an Al–Cu–Mg–Ag alloy

Assessment of long-term stability of an aluminium alloy exposed to elevated temperatures is important in the design of lightweight aerospace structures. The manner in which differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) are used together in monitoring microstructural evolution, and thereby assess phase stabilities in an Al–5.1Cu–0.8 Mg–0.5 Ag–0.7 Mn–0.13 Zr (wt%) alloy, are described. DSC thermograms of the alloy, spanning room temperature to 400°C, revealed the presence of two endotherms and an exotherm. TEM investigation has identified these thermal events to be associated with , S, and precipitates. Quantitative TEM was used to measure diameter, thickness, number density, and volume fraction of the precipitates in the alloy exposed at 135°C for times as long as 3000 h. The quantitative TEM results are correlated with the DSC signatures relating to precipitation, dissolution, and coarsening reactions affecting the , S, and precipitates in the exposed alloy.     

Short transverse fracture of Al–Li–Cu–Mg–Zr extrudate

Abstract

The short transverse fracture toughness of an Al–Li–Cu–Mg–Zr extrudate was determined as a function of aging condition and testing temperature. To elucidate the underlying micromechanisms, the short transverse fracture surfaces of the extrudate were characterised via scanning electron microscopy, grain boundary precipitates and precipitation free zones were identified via transmission electron microscopy, and segregation of elements to grain boundaries was analysed using secondary ion mass spectrometry. Three principal observations were made as follows. First, with increasing aging time, the short transverse toughness of the extrudate increased when tested at room temperature, but decreased at liquid N₂ temperature, whereas with decreasing testing temperature, it remained essentially constant for the underaged condition, and decreased sharply for the peak aged and overaged tempers. Second, in addition to regions exhibiting shallow dimples, smooth ‘featureless’ zones were revealed on the short transverse fracture surfaces, which are intergranular in nature for all the specimens tested. The area fraction of the featureless regions decreased noticeably with increasing aging time when tested at room temperature, and increased markedly with decreasing testing temperature for the peak aged and overaged conditions. Third, segregation of Li, Si, Na, and H was detected for both the underaged and overaged specimens, and also of K for the underaged specimens only. In general, the enhancement of the room temperature short transverse toughness with aging and the negative effect of cryogenic temperature on fracture toughness are in obvious contrast to the in plane toughness behaviour reported in the literature, the featureless character of the short transverse fracture and its connection with poor toughness seldom having been emphasised. Based upon the present study, segregation induced brittleness is proposed as the critical micromechanism responsible for grain boundary weakness, and thus for the poor short transverse fracture toughness.

MST/1829     

Effect of Sm on hydrogen storage performance of La–Sm–Mg–Ni alloys

In this study, Sm was adopted in order to completely replace the expensive Pr/Nd elements in the A2B7 type alloy. The results indicate that Sm is a favourable element for forming Ce2Ni7 type and Ce5Co19 type phases. With the increasing amount of Sm, the discharge capacity of the alloy retains a value of 283·3 mAh g^?1 at the current density of 1200 mA g^?1. The maximum discharge capacity of the alloys increases with the increasing Sm content when Mg content is relatively low. By optimising the composition and processing technology, the cycle life the alloy enhances from 74 cycles to more than 540 cycles, and the maximum discharge capacity also increases from 300 to 355 mAh g^?1.