Evolution Of Cast Research Articles

Influence of pre-stretching and annealing on microstructure and mechanical properties evolution of twin-roll cast Mg-2Al-1Zn-1Ca (wt.%) plates

Pre-stretching and annealing treatments were conducted on twin roll cast Mg-2Al-1Zn-1Ca (AZX211, in wt.%) plates with a rare earth-like texture. Varying amounts of deformation were applied along the rolling direction (RD) and transverse direction (TD) of AZX211 alloy in order to modify its mechanical properties at room temperature. The results demonstrate that pre-stretching treatment effectively enhances the yield strength (YS), especially along the RD. The strengthening mechanism is attributed to the production of a large number of dislocations and sub-grain boundaries, but the work-hardening ability of the plate will be greatly weakened. Additionally, annealing treatment substantially improves the plasticity and in-plane anisotropy and restores the work-hardening ability. The notable distinction in the pre-stretching process between different directions lies in the underlying deformation mechanism. In case of RD, deformation is predominantly governed by the slip mechanism of {0002} 〈11−20〉 basal slip and {10−10} 〈11−20〉 prismatic slip, while along the TD, deformation is primarily controlled by {0002} 〈11−20〉 basal slip without significant twinning deformation. When a 6 % pre-stretching is conducted, the initial rare earth-like texture of the sample transforms into a symmetrically distributed double-peak basal texture, accompanied by grain refinement. This texture transformation is chiefly due to the dominance of {0002} 〈11−20〉 basal slip-driven deformation. Moreover, the annealed sample maintains a strong basal texture, owing to strain-induced recrystallization.

Microstructural evolution and mechanical performance of cast Mg-3Nd-0.2Zn-0.5Zr alloy with Y additions

This work investigated the effects of different Y additions (0, 1.5, 3.0 and 4.5 wt.%) on the microstructural evolution and mechanical performance of cast Mg-3Nd-0.2Zn-0.5Zr alloy. The results show that as the Y content increases, the key secondary phases in as-cast alloys change from the Mg12Nd type to the Mg24Y5 type. Meanwhile, the number density of Zn-Zr particles in the grains of as-quenched alloys gradually decreases. HAADF-STEM observations of peak-aged samples reveal that element Y is greatly enriched in the globular β′ precipitates, leading to a significantly increased volume fraction and promoted precipitation kinetics of β′ precipitates, resulting in enhanced strength of the alloy. Tensile tests reveal that, with the addition of 4.5 wt.% Y, the yield strength of the base alloy is substantially increased by 88 and 61 MPa after being aged at 200 and 225 °C under peak-aged conditions, respectively.

Creep behavior and microstructure evolution of heat-resistant Mg-Sm-Yb-Zn-Zr alloy

In this work, we investigated creep behavior and microstructure evolution of cast Mg-4Sm-2Yb-0.6Zn-0.4Zr alloy. The alloy exhibited temperature-dependent stress exponents (n = 4.7, 5.8, and 7.2 at 200, 225, and 250 °C, respectively) and high creep activation energies ranging from 112 kJ/mol to 504 kJ/mol. Given the considerable influence of the temperature on the minimum creep rate, a normalized stress exponent of ∼4 was derived, implying that dislocation creep was operative. Abnormally high creep activation energies could be associated with the thermally stable intermetallic at grain boundaries and high density of precipitates within the α-Mg matrix. An analysis of the dislocation substructure confirmed that the main creep mechanisms were both cross-slip and climb of <a> dislocations. During creep, the precipitation of both prismatic β phases and basal γ’’ phases in the α-Mg matrix formed closed volumes, effectively arresting dislocations and contributing to the higher creep resistance than the majority of creep-resistant Mg alloys, such as traditional Mg-RE-based cast alloys and die-cast Mg benchmark alloys.

Regulative effect of Mg/Si ratio on microstructure evolution and mechanical properties of cast Al-Li-Mg-Si alloys

The effect of the Mg/Si ratio of Al-2.5Li-1Cu-0.8Mg-0.8Si, Al-2.5Li-1Cu-1.6Mg-0.8Si, and Al-2.5Li-1Cu-2.4Mg-0.8Si alloys on the microstructure evolution and mechanical properties was investigated. The results show that the primary phases and their morphologies in the as-cast alloys are found to vary with the Mg/Si ratio. The improvement of Mg/Si ratio of as-cast alloys promotes the formation of Mg2Si primary phase at the expense of the AlLiSi primary phase. Moreover, a tiny amount of TB-Al7.5Cu4Li phase transforms into S-Al2CuMg phase with the increase of Mg content. In addition, the increase of Mg/Si ratio also causes the Cu-rich intergranular phase distributed along crystal boundary to Si-rich intergranular phase. After ageing treatment, the precipitation sequence as a function of Mg/Si ratio is as follows: δ/δ′+AlLiSi (Mg/Si is ∼1) → δ/δ′+β′-Mg2Si+AlLiSi (Mg/Si is ∼2) → δ/δ′+β′-Mg2Si (Mg/Si is ∼3). A good combination of strength and ductility can be obtained in Al-2.5Li-1Cu-2.4Mg-0.8Si alloy after solution and ageing. The rod-like β′-Mg2Si precipitate has a positive influence on the comprehensive mechanical properties of the alloy.

The Hardness Evolution of Cast and the High-Cycle Fatigue Life Change of Wrought Ni-Base Superalloys after Additional Heat Treatment.

Concerning the use of modern technologies and manufacturing systems in the production of high-stress components from Ni-base superalloys and the optimization of the production process, knowledge of the microstructure–mechanical properties relationship is very important. The microstructure of Ni-base superalloys is very closely related to the chemical composition. With the high number of alloying elements, various phases are presented in the structure of Ni-base superalloys, which have a predominantly positive effect on the mechanical properties, but also phases that reduce, in particular, the heat resistance of these materials. The aim of the presented paper is the quantification of structural parameters of two types of cast alloys, ZhS6K and IN738, where the effect of dwell at 10 and 15 h at 800 °C on the change in morphology and volume fraction of the γ′-phase precipitate was studied. The detected changes were verified by the Vickers hardness test. The IN718 superalloy was chosen as a representative of the wrought superalloy. This alloy was also annealed for 72 h at a temperature of 800 °C, and the quantification of structural parameters was performed by EDS mapping and TEM analysis. Another partial goal was to assess the effect of changes in the volume fraction of the γ′-phase and δ-phase on the change in the high-cycle fatigue life of superalloy IN 718. This superalloy was tested by dynamic cyclic loading with cycle asymmetry parameter R = −1 at an ambient temperature of 22 ± 5 °C and at a temperature of 700 ± 5 °C and with cycle asymmetry parameter R < 1 (three-point bending load) after annealing at 700 °C/72 h. The results of the quantitative analyses and fatigue tests will be further used in optimizing the design of Ni-base superalloy components by modern technologies such as additive technologies for the production of turbine blades and implemented within the philosophy of Industry 4.0.

Microstructural evolution and flow behaviour in hot compression of as-extruded Mg–Gd–Nd–Zn–Zr alloy

ABSTRACT Hot deformation behaviour of as-extruded Mg–5Gd–2.5Nd–0.5Zn–0.5Zr alloy was investigated using compression test at a temperature range of 350–500°C and strain rates of 0.001–1 s−1. Microstructural evolution of cast and homogenised alloy following high-temperature deformation was captured by optical and scanning electron microscopy. Energy dispersive spectrometer results indicated that cast and homogenised samples consisted of eutectic compositions were mainly enriched in Nd and Gd. The flow stress was fairly well fitted by the hyperbolic sine equation where the calculated average activation energy was 297.81 kJ/mol. Hot deformation of the alloy was strongly affected by the high rare-earth metal (RE) constituent, and manifested by twining phenomenon at a temperature below 350°C and by dynamic recrystallization (DRX) and DRX-second phase interaction above 350°C.

Correction to: Effect of Strain Hardening and Aging Processes on Microstructure Evolution, Tensile and Fatigue Properties of Cast Ti-6Al-2Sn-2Zr–2Mo-1.5Cr-2Nb-0.1Si Alloy

The effect of strain hardening and aging processes on microstructure, tensile and fatigue properties was investigated on cast TC21 samples with a chemical composition of Ti-6.1Al-2.96Mo-2.11Nb-1.98Sn-2.05Zr-1.44Cr-0.1Si. Plastic deformation (strain hardening) was applied on swaged samples at room temperature with 2%, 3% and 4% strain. By applying aging process at 575°C for 4 hr, secondary α-platelets were precipitated in the transformed β-phase. Maximum hardness (HV440) was achieved for 4%def. + aged samples. However, minimum hardness (HV323) was recorded for aged samples. Maximum ultimate tensile strength (1311MPa) and elongation (14%) were obtained for 4% def. + aged samples due to presence of high amount of dislocation density as well as precipitation of secondary α-platelets in the residual β-phase. Minimum ultimate tensile strength (1020MPa) and elongation (3%) were reported for as-cast samples. Theoretical study using ANSYS software program was carried out for estimating fatigue limits for investigated samples. For validating the theoretical results, experimental test was done using rotating bending fatigue testing machine on three selected conditions of swaged, 2%def. + aged and 4%def. + aged. Maximum estimated fatigue strength of 775 MPa was obtained for 4%def. + aged samples, and the experimental one was 755 MPa. Hence, the difference between estimated and experimental fatigue limits for 4%def. + aged samples was less than of 3%.

The role of Yb content on the microstructural evolution and mechanical characteristics of cast Mg-9Gd-0.5Zn-0.2Zr alloy

Inspections on microstructural design suggest that a high-strength Mg alloy can be achieved via the generation of co-precipitation of prismatic and basal precipitates with high number density and large aspect ratios. Currently, there is a lack of feasible approaches to generating such a microstructure. This work investigated the specific role of various Yb contents on the precipitation behavior, solute segregation and mechanical performance of cast Mg-9Gd-xYb-0.5Zn-0.2Zr alloys (x = 0, 0.5, 1 wt%). It was found that, the age hardening response of Mg-9Gd-0.5Zn-0.2Zr alloy could be significantly improved as the Yb addition increased, primarily ascribed to introduction of dense distribution of both prismatic and basal matrix precipitates involving γ′′, β′ and β1. Solute segregation of Yb had been examined utilizing high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), revealing the evidence of strong Yb segregation in both prismatic β′, β1 and basal γ′′ precipitates. Quantitative TEM analysis indicated that the increasing Yb addition was found to improve the number density of γ′′, β′ and β1 during isothermal ageing at 225 °C. The substantial improvement on yield strength (~84 MPa) in peak-aged alloy was thereby achieved due to the co-precipitation of dense prismatic and basal strengthening phases associated with Yb addition (1 wt%). However, in addition to the promoted precipitation of these strengthening phases, Zn–Zr particles were confirmed to act as favorable nucleation sites for prismatic β1 phases in the under-aged condition. During prolonged ageing time, the addition of 1 wt% Yb was found to greatly accelerate the growth of these preferentially formed β1 phases and part of β1 transformed in situ into β phases, accompanied by the gradual developments of matrix precipitate-free zones (PFZs). The greatly improved uneven distribution of these coarse β-type phases concomitant with widened PFZs primarily led to the significant reduction in ductility as the Yb content increased up to 1%.

Flow Stress Behavior and Microstructural Evolution of DC Cast 7065 Aluminum Alloy During Hot Compression Deformation

The deformation behavior and microstructure evolution of DC cast 7065 aluminum alloy was investigated in the temperature range of 340-460 ℃ and strain rate range of 0.1-8 s-1. The flow stresses of the 7065 alloy are forceful function of deformation strain rate and temperature. The peak stress raises with reducing compression temperature, and at a designated deformation temperature, the peak stress increases with the increasing of strain rate. The hot deformation equation of the alloy is generated, and the deformation activation energy of the alloy is 117.869 kJ/mol. When the samples were deformed above 380℃, the α-aluminum dendrite in the initial microstructure was replaced by recrystallized grains, dynamic recrystallisation occurred during compression.

Development of processing maps for DC cast 7065 aluminum alloy

The deformation behavior and microstructure evolution of DC cast 7065 aluminum alloy was studied in the temperature range of 340-460 °C and strain rate range of 0.1-8 s-1. Processing maps were developed to evaluate the efficiency of the hot deformation and to identify the instability region. The results show that the optimum range of processing conditions are in the strain rate range of 0.01-0.1 s-1 and temperature range of 380-410 °C, where the efficiencies are much higher when compared to other regions. The peak efficiencies for the 7065 alloys is evaluated in the region of T=380-460 °C and ε=0.01-0.1 s-1. Recrystallized grain was observed under these deformation conditions. The dynamic softening is more pronounced at higher deformation strain rate and deformation temperature.

Effect of the addition of cerium on the microstructure evolution and thermal expansion properties of cast Al-Cu-Fe alloy

The evolution of the microstructure and the variation in the thermal expansion properties of the Al 63 Cu 25 Fe 12 alloy by the addition of different amounts of cerium (Ce) are investigated by x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). Herein, a new series of quasicrystal alloys containing Ce are prepared. Results revealed that the Al 63 Cu 25 Fe 12 alloy contains icosahedral quasicrystal phase (I-phase), λ − Al 13 Fe 4 phase, β − Al 0.5 Fe 0.5 phase and Al 2 Cu 3 phase. The addition of Ce is confirmed to lead to grain refinement, formation of the Al 13 Ce 2 Cu 13 phase, disappearance of the λ − Al 13 Fe 4 phase. Furthermore, the area fraction of the I-phase in the alloy is confirmed to reach the maximum value, and the linear expansion coefficient of the alloy is the lowest due to the addition of Ce of up to 1 at%. The addition of Ce can reduce the linear expansion coefficient of the Al 63 Cu 25 Fe 12 alloy by ∼20%. The contribution of Ce will render better prospects for the application of Al-Cu-Fe-Ce materials.

Microstructural evolution and mechanical properties of cast high-Li-content TiB2/Al-Li-Cu composite during heat treatment

The microstructural evolution and mechanical properties of cast high-Li-content TiB2/Al-Li-Cu composite during heat treatment were systematic investigated by a combination of various techniques, including transmission electron microscopy (TEM) with HAADF-STEM mode, electron backscatter diffraction (EBSD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The coarse secondary phases, mixed with clusters of relatively larger TiB2 particles, distributed along grain boundaries were observed in as-cast state. And most of them dissolved into the α-Al matrix after a two-stage solution treatment. The grain size of the studied composite exhibited excelled thermal stability owing to effective pinning grain boundaries by the stable particles at the elevated temperature, resulting in no significant increase after solution treatment. The studied composite showed a strong age-hardening response with the peak-hardness was obtained in about 160 h at 175 °C. TEM results showed much fine δ′ precipitates were uniformly distributed within grains after quenching and it coarsened with the increasing age duration. Fine plate-like θ′ and T1 precipitates were observed in the under-aged (UA, aged for 8 h) condition. The rate of precipitation and growth in its diameter was much greater than its coarsening rate, resulted in the large aspect ratio and high number density of T1 and θ′ precipitates were visible in the peak-aged (PA) condition. Finally, a slight decline in hardness was observed in the over-aged (OA) condition due to the apparent coarsening of θ′ and T1 precipitates. This precipitation behavior was further verified by DSC. After appropriate heat treatment, a good comprehensive mechanical properties could be obtained in the composite.

Effect of precipitation state on texture evolution in cold-rolled continuous cast AA 2037 aluminum alloy

The texture evolution of continuous cast (CC) AA 2037 aluminum alloy during cold rolling was investigated by X-ray diffraction as a function of the precipitation state. The results show that the various precipitates produced during aging reduce the rate of disappearance of the cube + r-cube component, and that the said rate decreases with increasing aging time. At large strains the θ′ and θ precipitates enhance significantly the rate of disappearance of the remainder component, which implies that the shear bands formed in the grains with remainder orientations accelerate the texture development. The state of precipitation has a significantly effect on the distribution of orientation intensities along the β fiber. With increasing aging time, more initial cube-oriented grains are rotated to the C orientation rather than the B orientation, which leads to a more rapid increase in the intensity of the C orientation with increasing rolling reduction.

Microstructural evolution and mechanical properties of cast Al-2Li-2Cu-0.5Mg-0.2Zr alloy during heat treatment

The microstructure, electrical conductivity and mechanical properties of cast Al-2Li-2Cu-0.5Mg-0.2Zr alloy during heat treatment were investigated. The results indicated that a population of secondary phases enriched along grain boundaries in as-cast studied alloy, most of which dissolved into the α-Al matrix after solution treatment. Profound enhancement in mechanical properties of the studied alloy was obtained after T6 heat treatment. TEM observations revealed competitive precipitation of T1 (Al2CuLi) and S′ (Al2CuMg) phases during ageing, while no θ′ (Al2Cu) phase was observed. The anomalous decrease in conductivity observed during ageing was attributed to the precipitation of T1 phases. Fine δ′ (Al3Li) particles were homogeneously distributed after quenching, gradual coarsening of which was observed with prolonged ageing time. As ageing proceeded, the δ′ coarsened and δ′-Precipitate-Free Zones (PFZs) developed, resulting in diminishing ductility observed from as-quenched to peak-aged state. Precipitation and continuous coarsening of T1 phases kept on at the expense of gradual δ′ dissolution. The improvements of ductility observed in over-aged samples arose mainly from the presence of T1, S′ phases, Al3(Li,Zr) composite precipitates and progressive δ′ dissolution. Moreover, continuous coarsening of T1 and S′ phases contributed primarily to the strength loss in over-aged studied alloy.

Effect of volume fraction of LPSO phases on corrosion and mechanical properties of Mg-Zn-Y alloys

Microstructural evolution, corrosion behavior and mechanical properties of cast Mg-Zn-Y alloys as a function of volume fraction of long period stacking ordered (LPSO) phases were investigated. Results revealed that 18R-LPSO phase was formed in Mg-0.9%Zn-1.6%Y (ZW12), Mg-2.1%Zn-5.2%Y (ZW25) and Mg-3.1%Zn-7.6%Y (ZW38) alloys. LPSO phases in these alloys acted as micro-cathode to accelerate corrosion progress due to their nobler nature than that of α-Mg matrix. The galvanic-couple effect between LPSO phases and α-Mg matrix dominated the corrosion rate of the cast Mg-Zn-Y alloys in the long-term corrosion process. As a result, ZW12 alloy displayed the best corrosion resistance due to the least volume fraction of micro-cathodes (i.e. LPSO phases). In addition, compared with ZW25 alloy, the compact and thick LPSO phases in ZW38 alloy hindered the corrosion progress to a small degree since it was not preferentially oriented against corrosion front. The shape of corrosion pits was correlated to the shape of Mg dendrites that was a result of the volume fraction and distribution of LPSO phases. LPSO phases could enhance mechanical strength, but the increment was slight when the volume fraction of LPSO phases reached up to 20.3%.

Microstructural evolution and mechanical properties of cast Al-3Li-1.5Cu-0.2Zr alloy during heat treatment

The microstructures and mechanical properties of cast Al-3Li-1.5Cu-0.2Zr alloy during heat treatment were investigated. The results showed that large amounts of secondary phases distributed along grain boundaries in as-cast state, and most of them dissolved into the α-Al matrix after solution treatment. The alloy had a very strong age-hardening response with the peak-hardness that was more than double for the as-quenched. TEM showed much fine δ′ (Al3Li) particles were homogeneously distributed after quenching, and long δ′ phases were observed during ageing. Fine T1 (Al2CuLi) precipitate was visible after ageing for 8h at 175°C, and both its number density and size increased with the increase of ageing time. Apart from δ′ and T1, θ′ (Al2Cu) phases of large aspect ratio were precipitated in the over-aged condition. As the ageing proceeded, the δ′ particles coarsened and the Precipitate-Free Zones (PFZs) developed, resulting in poor ductility and premature failure. The studied alloy was largely strengthened by the δ′ phase during ageing. After ageing at 175°C for 32h, a good mechanical property with ultimate tensile strength (UTS)=382MPa, yield strength (YS)=307MPa and elongation (EL)=2.9% was obtained.

Two-phase quasi-equilibrium in β-type Ti-based bulk metallic glass composites.

The microstructural evolution of cast Ti/Zr-based bulk metallic glass composites (BMGCs) containing β-Ti still remains ambiguous. This is why to date the strategies and alloys suitable for producing such BMGCs with precisely controllable volume fractions and crystallite sizes are still rather limited. In this work, a Ti-based BMGC containing β-Ti was developed in the Ti-Zr-Cu-Co-Be system. The glassy matrix of this BMGC possesses an exceptional glass-forming ability and as a consequence, the volume fractions as well as the composition of the β-Ti dendrites remain constant over a wide range of cooling rates. This finding can be explained in terms of a two-phase quasi-equilibrium between the supercooled liquid and β-Ti, which the system attains on cooling. The two-phase quasi-equilibrium allows predicting the crystalline and glassy volume fractions by means of the lever rule and we succeeded in reproducing these values by slight variations in the alloy composition at a fixed cooling rate. The two-phase quasi-equilibrium could be of critical importance for understanding and designing the microstructures of BMGCs containing the β-phase. Its implications on the nucleation and growth of the crystalline phase are elaborated.

The impression creep behavior and microstructure evolution of cast and cast-then-extruded Mg–10Gd–3Y–0.5Zr (wt%)

The impression creep behavior of Mg–10Gd–3Y–0.5Zr (wt%, GW103) was investigated by flat cylindrical indenter experiments at temperatures ranging from 200°C to 325°C. The punching stresses, which were calculated based on the indenter dimensions, varied from 50MPa to 505MPa. Samples were examined in the peak-aged cast condition (cast-T6) and in the cast-then-extruded plus peak-aged condition (ex-T5). Using a power–law relationship, the creep stress exponent (n) varied from 1.4 to 5.1 for the cast-T6 alloy, where lower values were obtained at lower temperatures and stresses. The creep activation energy (Q) increased from 87 to 191kJ/mol with increasing stress. For the ex-T5 alloy, the n values were 2.2, 3.4 and 3.4 at 200°C, 250 and 300°C, respectively. The Q value increased from 121 to 165kJ/mol with increasing stress. However, by using a hyperbolic sine relationship, single activation energies of 93 and 134kJ/mol were obtained for the cast-T6 and ex-T5 alloy, respectively. The zone at the edges of the indenter underwent the largest stress and strain, resulting in broken grain boundaries. Extension twinning occurred both in the zone at the edges of the indenter and underneath the indenter face for the cast alloy, while no twinning was observed for the extruded alloy. Intergranular cracking was observed in the zone at the edges of the indenter for the tests under high temperature and high stress.

Bakhtin and the actor (with constant reference to Shakespeare)

The Bakhtin we know best is something of a lyricophobe and theatrophobe. This is surprising, since he loves the act of looking. His scenarios rely on visualized, collaborative communion. He cares deeply about embodiment. Does he care about the tasks that confront the actor? Not the improvising clown of carnival (carnival is theater only in the broad sense of performance art), but the trained artist who performs a play script on stage? In discussing these questions, this essay draws on two suggestive places in Bakhtin’s writing where he addresses the actor’s art. One is from the mid-1920s; the other (1944), is on Shakespearean tragedy. If Bakhtin has a theatrical imagination, it will be found here. His grasp of an actor “living in” to a role and his comments on the evolution of the European stage cast his better-known ideas of dialogue, comedy, seriousness and the sacred into unexpected perspective.

Microstructure Evolution of Conventional and Semi-Solid Cast of A356 Aluminium Alloy with Addition of Inoculant

This paper investigated the effect of inoculant, Al-5Ti-1B in conventional and semi-solid casting A356 aluminium alloy. A356 aluminium alloy was melted at 850 oC and poured at 680 °C directly into the steel mould and on the inclined slope into steel mould. Inoculant was added in various percentages of 1 wt.%, 2 wt.%, 3 wt.% and 3.5 wt.% in A356 aluminium alloy melt. Microstructure and microhardness were characterized using optical microscope and Vicker’s microhardness tester. The addition of master alloy up 3.5 wt.% Al-5Ti-1B in conventional casting refined dendritic structure with average grain size of 33.41 μm. The microstructures of semi-solid A356 aluminium alloy with addition of Al-5Ti-1B consist of equiaxed structure of α-Al. Further addition of Al-5Ti-1B refined the globular structure of α-Al. The higher hardness was achieved for A356 alloy prepared using semi-solid with addition of 3.5 wt.% of Al-5Ti-1B.