Evolution of the structure and mechanical properties of sheets of the Al–4.7Mg–0.32Mn–0.21Sc–0.09Zr alloy due to deformation accumulated upon rolling

The mechanical properties and microstructure of sheets of an Al–4.7Mg–0.32Mn–0.21Sc–0.09Zr alloy deformed and annealed after rolling have been investigated. The total accumulated true strain was ε_f = 3.33–5.63, and the true strain at room temperature and at 200 °C was ε_с = 0.25–2.3. The strength properties of the sheets (yield stress σ_0.2 = 495 MPa and ultimate tensile strength σ_u = 525 MPa) in the deformed state were greater than those after equal-channel angular pressing (ECAP) deformation. The mechanical properties of the deformed sheets after annealing depended on the size of subgrains inside the deformed grains bands with high-angle grain boundaries (HABs). With the increase in the annealing temperature from 150 to 300°С, the subgrain size increased from 80 to 300 nm. The relative elongation δ in the as-cast state and after annealing at 200–250°C (δ = 40–50%) was higher than that after annealing at 300–370°C (δ = 24–29%).     

Microstructure evolution of 7050 aluminum alloy during hot deformation

Hot compression of 7050 aluminum alloy was performed on Gleeble 1500D thermo-mechanical simulator at 350 ℃ and 450 ℃ with a constant strain rate of 0.1 s-1 to different nominal strains of 0.1, 0.3 and 0.7. Microstructures of 7050 alloy under various compression conditions were observed by TEM to investigate the microstructure evolution process of the alloy deformed at various temperatures. The microstructure evolves from dislocation tangles to cell structure and subgrain structure when being deformed at 350 ℃, of which dynamic recovery is the softening mechanism. However, continuous dynamic recrystallization (DRX) occurs during hot deformation at 450 ℃, in which the main nucleation mechanisms of DRX are subgrain growth and subgrain coalescence rather than particle-simulated nucleation (PSN).     

Microstructure and mechanical properties of Mg–Zn–(Nd)–Zr alloys with different extrusion processes

The effect of Nd addition and the in?uence of extrusion processes on the microstructure and mechanical properties of Mg–6Zn–0.5Zr(ZK60) and Mg–6Zn–1.5Nd–0.5Zr(ZKNd602) alloys were investigated. Nd element can obviously re?ne the microstructure of both as-cast and asextruded Mg–Zn–Nd–Zr alloy. All of the extruded alloys exhibit a bimodal grain structure composed of equiaxed?ne recrystallized(DRXed) grains and elongated coarse un DRXed grains. It is necessary to achieve high strength,particularly the yield strength, for ZKNd602 alloy, when it is extruded with a lower extrusion temperature, a suitable extrusion ratio and a relatively lower extrusion ram speed. In this study, the ultimate tensile strength(UTS),yield strength(YS) and elongation(El) of the extruded ZKNd602 alloy were 421 MPa, 402 MPa and 6.7 %,respectively, with extrusion temperature of 290 °C, extrusion ratio of 18:1 and a ram speed of approximate0.4 mm·s~(-1). Meanwhile, the extrusion process has obvious effects on the room-temperature properties but weak effects on the high-temperature properties.     

Effect of torsion conditions under high pressure on the structure and strengthening of the Zr–1% Nb alloy

The effect of temperature and degree of deformation upon severe plastic deformation by torsion under a high pressure on the structure, phase composition, and microhardness of the industrial zirconium Zr–1% Nb alloy (E110) has been studied. The high-pressure torsion (HPT) (with N = 10 revolutions) of the Zr–1% Nb alloy at room temperature results in the formation of grain–subgrain nanosize structure with an average size of structural elements of 65 nm, increase in the microhardness by 2.3–2.8 times (to 358 MPa), and α-Zr → β-Zr and α-Zr → ω-Zr phase transformations. The increase in the HPT temperature to 200°C does not lead to a decrease in the microhardness of alloy owing to the increase in the fraction of ω-Zr phase, though the average size of structural elements increases to 125 nm. The increase in the temperature to 400°C during HPT with N = 10 revolutions leads to the grain growth in the α-Zr grain structure (~90%) to 160 nm and a decrease in the microhardness to 253–276 HV.     

Microstructure evolution and mechanical behavior of as-cast,heat treated and directionally solidified Fe–15Al–10Nb alloys

Fe–15Al–10Nb (at.%) alloys containing Laves phase fibers embedded in a disordered α-(Fe,Al) matrix were investigated in as-cast, heat treated and directionally solidified condition. Microstructure consisted of either duplex structure of primary dendrites and eutectic (as-cast and heat treated) or fully eutectic structure (directionally solidified). Nanoindentation on the Laves phase fibers revealed their anisotropic features as well as the onset of dislocation plasticity. Compression testing showed the yield strength anomaly, which occurred in the 500–650 °C range. Directional solidified alloy exhibited the lowest strength fracture toughness whereas the as-cast alloy had the highest strength and fracture toughness. The value of stress exponent obtained from the strain rate dependence of the flow stress indicated that the dislocation climb mechanism dominated the creep process. Deformation mechanisms were also discussed and related to the microstructure evolution.     

Coherency loss of Al3(Sc,Zr) precipitates by deformation of an Al–Zn–Mg alloy

Al alloys with additions of Sc and/or Zr exhibit a reasonably stable grain structure due to a uniform distribution of coherent Al₃(Sc,Zr) precipitates that forms at temperatures >300 °C. These precipitates are stable up to the solution treatment temperature and are able to pin subgrain and grain boundaries, inhibiting grain coarsening. The crystallographic structure of these precipitates presents a L1₂ superstructure coherent with the face-centred cubic Al matrix. Changes in the orientation relation between precipitates and the matrix are described in deformed, recovered and partially recrystallized samples of extrusions of AW7010 (AlZn6Mg2Cu2). The coherency of the intracrystalline Al₃(Sc,Zr) precipitates present in the extrusions is lost by severe deformation performed by an equal channel angular pressing process, which produced a fine-grained microstructure. The deformed sample recovers, forming a subgrain structure with restored coherency of the Al₃(Sc,Zr) precipitates. Rapid heating to 470 °C causes partial secondary recrystallization, which transforms the precipitates within the recrystallized grains into incoherent groups of particles that maintain their original orientation with each other.     

Microstructure and Properties of TIG/FSW Welded Joints of a New Al-Zn-Mg-Sc-Zr Alloy

A new Al-Zn-Mg-Sc-Zr alloy with low Sc content was welded by tungsten inert gas (TIG) and friction stir welding (FSW) techniques. The microstructure and properties of those two welded joints were investigated by property tests and microstructural observations. The results show that the new Al-Zn-Mg-Sc-Zr alloy has desirable welding property. The ultimate tensile strength and welding coefficient of the TIG joint reach 405 MPa and 76.7%, respectively, and in FSW joint those property values reach 490 MPa and 92.6%, respectively. The studied base metal has a deformed fibrous subgrains structure, many nano-scaled Al₃(Sc,Zr) particles, and very fine aging precipitates. In the TIG joint, the fusion zone consists of coarsened dendritic grains and the heat-affected zone (HAZ) has fibrous micro-scaled subgrains. The FSW welded joint is characterized by a weld nugget zone, thermo-mechanically affected zone (TMAZ), and HAZ. Due to plastic deformation around the rotating pin and anti-recrystallized effectiveness of Al₃(Sc,Zr) particles, the weld nugget zone has a very fine subgrain structure. The TMAZ experiences some dissolution of aging precipitates. Coarsening of aging precipitates was observed in the HAZ. The better mechanical properties of the FSW joint are derived from a fine subgrain structure and homogeneous chemical compositions.     

Effects of Minor Zr and Sr on As-Cast Microstructure and Mechanical Properties of Mg-4Y-1.2Mn-1Zn (wt.%) Magnesium Alloy

The effects of minor Zr and Sr on the as-cast microstructure and mechanical properties of the Mg-4Y-1.2Mn-1Zn (wt.%) alloy were investigated using optical and electron microscopies, differential scanning calorimetry (DSC) analysis, and tensile and creep tests. The microstructural results indicate that small additions of Zr and/or Sr to the Mg-4Y-1.2Mn-1Zn alloy do not cause an obvious change in the morphology and distribution of the Mg₁₂YZn phase in the alloy. The tensile and creep tests indicate that, although small additions of Zr and/or Sr to the Mg-4Y-1.2Mn-1Zn alloy do not have obvious effects on the creep properties of the alloy, the tensile properties at room temperature and 300 °C for the alloys added with Zr and/or Sr are improved. Among the Zr- and/or Sr-containing alloys, the alloy specifically added with of 0.5 wt.% Zr + 0.1 wt.% Sr obtains the optimum tensile properties, and is followed by the alloys added with 0.5 wt.% Zr and 0.1 wt.% Sr.     

Studying recovery processes in a strain-hardened Al–Mg–Mn–Fe–Si alloy

The material of a shell structure subjected to 20-year use under ambient conditions has been studied. The structure and mechanical characteristics of a strain-hardened AMg6 alloy, as well as the effect of subsequent holdings of this alloy for 10–3000 h at temperatures of 50, 70, 80, 100, 130, 150, 180, and 220°C, on changes in its dislocation structure and mechanical characteristics have been investigated. It has been shown that, in the structures under study, the AMg6 alloy has a cellular structure with a high density of dislocations and the ultimate strength σ_u = 445.5 ± 2.5 MPa, the proof stress σ_0.2 = 326.5 ± 3.5 MPa, and the relative elongation δ = 11.7 ± 0.5%. Polygonization in the alloy occurs at a temperature of 220°C and the initial stage of the recovery process corresponds to a temperature range of 50–100°С in which the softening process can be divided into two stages, i.e., stage (1) of active softening due to the interaction of point defects with each other and stage (2) of the stabilization of the characteristics of the alloy.     

The annealing behaviour of deformed cube-oriented aluminium single crystals

Single crystals of the {001}〈100〉 cube orientation of a dilute single-phase Al–Si alloy have been deformed in plane strain compression at temperatures between 300 and 500°C at strain rates between 0.5 and 50/s. The stability of the cube orientation was found to be dependent on the deformation conditions, which is in agreement with previous work. The deformed crystals contained bands of subgrains of a range of sizes and misorientations. Detailed EBSD analysis of deformed and annealed crystals revealed a strong correlation between subgrain growth and misorientation, and analysis of the data enabled the mobility of low angle grain boundaries in the misorientation range 5–20° to be determined in the temperature range 300–450°C. It was found that the boundary mobility increased with increasing misorientation up to ∼15–20° and thereafter reached a plateau. The activation energies of migration were consistent with control by lattice diffusion of Si in Al and the activation energy was found to increase with increasing misorientation.     

Precipitation in ductile Fe–18Al–5Cr alloys with additions of Mo,W and C and effects on high-temperature strength

The strength of a Fe–Al-based alloy containing small additions of Mo, W and C has been determined from room temperature up to 800 °C, and the strain rate dependence of strength examined. Strength of the as-cast material is maintained at above 600 °C, but it is lost at higher temperatures, especially at slow strain rates. This behaviour is largely explained by solute hardening effects, with no sign of any precipitates forming. After a solution treatment, annealing material at 800 °C leads to the appearance of Fe–Mo–W carbides which provide better strength under conditions of high temperature and slow strain rate. The possibilities for improving high-temperature strength and creep behaviour by the formation of carbide or intermetallic precipitates are discussed.     

Effects of solution heat treatment on the microstructure, oxidation, and mechanical properties of a cast Ni3Al-based intermetallic alloy

Solution heat treatment is employed in an attempt to improve oxidation and mechanical properties of an as-cast Ni₃Al alloy (IC221M) at operation temperature, 900 °C. Solution heat treatment was hypothesized to have beneficial effects through dissolving γ Ni₅Zr eutectic into the matrix. The microstructures, oxidation behavior in air at 900 °C, and mechanical properties with aging times at 900 °C were examined after solution heat treatment of as-cast Ni₃Al alloy in Ar for up to 100 h at 1100 °C. The oxide penetration depth into the matrix was dramatically decreased and more homogeneous surface oxides were obtained relative to the no solution, treatment case. Hardness was improved by solution heat treatment due to a solid solution strengthening effect by Zr, but the tensile properties after solution heat treatment were not significantly different from those prior to treatment.     

Microstructure evolution of Al-Zn-Mg-Cu-Zr alloy during hot deformation

Compression tests of the Al-Zn-Mg-Cu-Zr(7055) alloy were performed at various strains and temperatures from 300 to 450°C under a constant strain rate between 10⁻² s⁻¹ and 1 s⁻¹. Microstructures during hot deformation were studied by transmission electron microscopy (TEM). Dislocation density, dislocation cells and subgrains of the deformed samples were investigated in detail and compared to make a better understanding of the microstructure evolution. The results showed that stress-strain curves under the experimental conditions belonged to the type of dynamic recovery. When the alloy deformed at various strains and 300°C, the microstructure underwent a process of disordered dislocations to cell structure, subgrain structure and subgrain coarsening. With the temperature increasing, subgrains grew and dislocation density in the interior decreased at a strain rate of 1 s⁻¹. At the temperature of 350°C, the average diameter of subgrains decreased, sub-boundaries broadened and dislocation density in the interior decreased when the strain rate was increased. The deformed samples of 7055 alloy had smaller subgrains than that of 7005 alloy at the same compression condition because of high alloy content.     

Microstructural evaluation and mechanical properties of Ir–Hf–Zr ternary alloys at room and high temperatures

Iridium is one of the most promising base metals for future high-temperature structural materials. Attempts to improve the high-temperature strength of Ir have involved solid-solution hardening and coherent hardening. Hf and Zr having a larger atomic size misfit with Ir were found to be the most effective solid-solution hardening and coherent hardening elements on Ir. The idea of multi-component alloying Ir by Hf and Zr was used for the improvement of high-temperature properties of Ir-based alloys in this work. The results show that the monolithic saturated fcc phase has an outstanding Vickers hardness at room temperature, whereas a dual-phase fcc/L1₂ structure is favorable for high-temperature strength and creep resistance. With a dual-phase fcc/L1₂ structure composed mostly of fcc phase, the Ir–5Hf–5Zr alloy has a 0.2% yield strength as high as 175 MPa, and a stable creep rate as low as 1.33 × 10⁻⁷ S⁻¹ at a stress of 40 MPa even at 1950 °C. Finally, a principle for the design of Ir-based alloy based upon the composition and microstructural morphology was discussed.     

Creep deformation of oxide-dispersion-strengthened Fe-40Al intermetallic: thermal and athermal contributions

The creep behaviour of an Fe-40Al alloy containing Y₂O₃ particles has been analysed combining microstructural information and experimental data obtained from mechanical tests. The creep strength of the alloy is controlled by the dislocation-particle attractive interactions. At 500°C the dislocation overcomes the dispersoid particles by a detachment-controlled process while at 700°C general climb is the controlling mechanism. Both processes are thermally activated such that vacancy diffusion through the lattice determines the velocity at which the obstacles can be overcome. The rapid fall in creep strength observed between 500 and 700°C has been explained by the rapid increase in diffusivity as vacancy concentration and mobility both increase dramatically.     

Effects of heat treatment on microstructure and mechanical properties of Mg-6Zn-4Sm-0.4Zr alloy

A new rare earth magnesium alloy(Mg-6 Zn-4 Sm-0.4 Zr, wt.%) was prepared by permanent mould casting. The microstructure and mechanical properties of the alloy sample in as-cast and various heat treatment situations were characterized with an optical microscope(OM), X-ray diffractometer(XRD), scanning electron microscope(SEM) equipped with energy dispersive spectroscope(EDS), transmission electron microscope(TEM) and mechanical tests at room temperature, respectively. The experimental results show that the as-cast alloy mainly consists of α-Mg, eutectic Mg_2Zn_3, MgZnSm and Mg_(41)Sm_5. These eutectic phases with continuous or semicontinuous morphology principally distribute along grain boundaries. Almost all the eutectic compounds dissolve in α-Mg and the grains have no obvious growth trend after optimum solution treatment at 490 °C for 18 h. Meanwhile, the ultimate tensile strength(UTS) of 229 MPa and elongation(EL) to rupture of 9.78% can be achieved through the optimal solution treatment, which increase by 37 MPa and 57.74%, respectively, compared with that of the as-cast alloy. Further aging treatments at 200 °C for different durations lead to the conspicuous increment of mechanical properties and prominent age-hardening response. Peak-aged alloy(treated at 200 °C for 12 h) reveals better mechanical properties(UTS 258 MPa, EL 9.42%, hardness 73.4 HV) compared with the same alloy treated in other aging conditions, which is mainly ascribed to precipitated Mg_2Zn_3 and MgZn_2 phases. Fracture analysis demonstrates that the as-cast alloy belongs to inter-granular and cleavage fracture patterns, while the solutionized alloy(treated at 490 °C for 18 h) reveals trans-granular and quasi-cleavage fracture modes. For the peak-aged alloy, the fracture pattern obeys the mixture of trans-granular and cleavage modes.     

Strength anomaly of the B2 phase in Ti–25Al–25Zr alloy

Mechanical behaviour of the single B2 phase in the alloy Ti–25Al–25Zr has been studied under compression with different strain rates at elevated temperatures. The alloy Ti–25Al–25Zr exhibits yield strength anomaly similar to those of the typical B2 intermetallics such as FeAl. The stress–strain curves of the alloy tested at 400 °C show type C serrations which are considered to be due to dislocation unlocking. Intersecting and straight slip lines are observed in specimens tested at 400 °C and 600 °C, respectively.     

Effect of minor Sc additions on structure,age hardening and tensile properties of aluminium alloy AA8090 plate

The grain structure, age hardening response, precipitate structure and tensile properties of AA8090 alloy plate without and with minor additions of Sc were investigated. Primary aluminide particles were present in all alloys. Sc additions ⩾0.43% resulted in refinement of the as-cast grain structure. Further investigations on 0.11% and 0.22% Sc containing alloys showed that the subgrain size was finer while the number density of nano-scale Al₃(Sc,Zr)/Al₃Li composite precipitates and the artificially aged hardness were higher for the Sc containing alloys. There was a marginal increase in the yield strength with a concomitant reduction in ductility with increasing Sc content in the alloys.     

热处理对Mg-5Zn-0.63Er合金显微组织及力学性能的影响

通过不同的热处理工艺研究含有准晶Ⅰ相的铸态Mg-5Zn-0.63Er(质量分数,％)合金的显微组织演变.结果表明:合金在480℃固溶10 h后,除有W相颗粒析出外,准晶Ⅰ相几乎全部固溶在基体中.固溶态Mg-5Zn-0.63Er合金在175℃下时效6～10h.合金在峰时效态的抗拉强度约为261MPa、伸长率为10.5％.合金拉伸强度的提高归因于杆状MgZn2相的析出.     

Creep deformation and microstructural change in extruded zn-al based alloy

Microstructural evolution and related phase transformation of an extruded eutectoid Zn-Al based alloy are studied in detail under creep deformation at 150°C. Lamellar structure in the extruded alloy spheroidized partially into fine grain structure. Also decomposition of a metastable ή_T phase and a four phase transformation. α+ε→T+η, were observed in the creep deformed alloy specimens. Creep rupture of the extruded Zn-Al alloy was studied in correlating with the creep induced phase transformation and microstructural changes.