Texture evolution in cold-rolled Mg-0.3Zn-0.1Ca, Mg-0.4Zn and Mg-0.1Ca (at.%) alloys during static recrystallization is monitored using a quasi-in-situ electron backscatter diffraction (EBSD) method. ...The quasi-in-situ EBSD results show that most of recrystallized grains formed in the early stage of recrystallization have randomised orientations in the ternary alloy and they grow uniformly during the recrystallization process. The formation and uniform growth of these recrystallized grains with randomised orientations give rise to a weak texture in fully recrystallized samples of the ternary alloy. A weak recrystallization texture also forms in the early stage of recrystallization in the two binary alloys, but it is gradually replaced by a strong basal texture via the preferential growth of recrystallized grains with specific orientations. The grain size in the ternary alloy is smaller than those in the two binary alloys at each stage of recrystallization, and the grain size distribution in the ternary alloy is significantly narrower than those in the two binary alloys after full recrystallization. Solute segregation to grain boundaries is observed in all three alloys in the fully recrystallized state. It is hypothesised that Zn and Ca atoms in the ternary alloy segregate strongly to high-energy boundaries of the recrystallized grains that would otherwise grow preferentially in the counterpart binary alloys, and that this co-segregation would significantly reduce the boundary mobility, by reducing grain boundary energy and enhancing solute dragging effect, and therefore lead to a more uniform growth of recrystallized grains with randomised orientations.
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The present study seeks to clarify the mechanism by which dilute additions of zinc (Zn) and calcium (Ca) improve ductility of Mg alloy sheet. Herein, the ductility and microstructure of fully ...annealed pure Mg and Mg-0.1Ca, Mg-0.4Ca, Mg-0.4Zn, and Mg-0.3Zn-0.1Ca (at.%) alloy sheet were systematically investigated and compared. It is found that the ternary alloy displays better ductility than either pure Mg or binary Mg-alloys, when fully recrystallized and possessing similar grain size. In the deformed grains of the ternary alloy, traces of basal and pyramidal slip and {101̅2} twins are observed, whilst only basal slip traces and {101̅2} twins are observed in the pure Mg and binary alloys. Grain boundary cracks are observed in all the tensile-tested alloys. However, significantly less grain boundary cracks are observed in the ternary alloy, posited to be due to enhanced grain boundary cohesion. These observations suggest that the combination of enhanced pyramidal slip and suppressed grain boundary cracking leads to the appreciably improved ductility of the Mg-0.3Zn-0.1Ca alloy sheet.
We clarified the role of Zn on the mechanical properties and texture evolution in Mg-1.2Al-0.5Ca-0.4Mn-xZn (wt.%, x = 0, 0.8 and 1.6) alloy sheets fabricated by twin-roll casting and hot rolling. The ...room temperature stretch formability of the solution-treated sheet is improved with increasing Zn content, x. The Mg-1.2Al-0.5Ca-0.4Mn-1.6Zn alloy shows excellent stretch formability with the largest Index Erichsen value of 8.2 mm due to a weak transverse direction split texture. The development of the transverse direction split texture is attributed to the preferential nucleation of recrystallized grains at double twin boundaries promoted by the moderate segregation of Zn and Al. Subsequent artificial aging at 170 °C for 2 h (T6) leads to a substantial increase in strength without loss of ductility. The peak-aged Mg-1.2Al-0.5Ca-0.4Mn-1.6Zn alloy exhibits a high tensile yield stress of 210 MPa with an excellent elongation of 30.1% because of the dense dispersion of Guinier Preston zones within the Mg matrix. The insights gained in this work would establish a base for rational design and fabrication of bake-hardenable magnesium alloy sheet with excellent room temperature formability and high strength.
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•This work established a base to design strong and formable magnesium alloy sheets.•The Zn addition is effective to achieve excellent room temperature formability.•The Zn addition changes recrystallization mechanism during the heat treatment.•The addition of Zn increases the number density of G.P. zone formed during aging.
Face-centered-cubic (FCC) Fe40Mn20Cr20Ni20 high-entropy alloys (HEAs) with a weigh of 50 Kg were fabricated by industrialized vacuum-induction melting. This alloy consists of a tetragonal σ phase and ...minority M23C6 carbides embedded in the continuous FCC matrix after thermomechanical treatments. A heterogeneous structure composed of a phase distribution and grain size is formed. The yield strength and ultimate tensile strength are increased from 398 MPa to 679 MPa at 10−4 s−1 to 743 MPa and 1412 MPa at 3000 s−1, respectively. Meanwhile, the elongation is slightly improved as the strain rate rises. The strain rate sensitivity under quasi-static tension is 0.0172, in contrast to 0.3978 under dynamic deformation. Upon dynamic tension, the simultaneous enhancements of both strength and ductility are attributed to the joint activation of multiple strengthening mechanisms. Deformation-induced twinning further improves the strain-hardening ability of the alloy. Besides, short range order may seriously hinder the dislocation movement, especially when the thermal activation of dislocations gradually fails at high strain rates, which limit the dislocation slip to a smaller scale and result in deformed sub-grains. In contrast, under quasi-static tension, only dislocation slip dominates, accompanied by dislocation entanglement and massive pile-ups. Moreover, a typical Johnson-Cook model was employed to predict the dynamic-flow behavior. This study sheds lights on the mechanical performance superiority from heterogeneous HEAs under dynamic tension and might open new insights for developing high-performance HEAs to resist dynamic impacts.
•The Fe40Mn20Cr20Ni20 high-entropy alloys (HEAs) with a weigh of 50 Kg.•Heterphase and heterostructure induced by different phases and grain sizes.•The deformation twins and subgrains lead to higher strain-rate sensitivity under dynamic tension.•Stack fault energy was calculated from thermodynamics and molecular dynamics simulation.•Critical twin stress was determined for the target HEAs.
Mg–1.2Al–0.3Ca–0.4Mn–0.3Zn (AXMZ1000) (wt%) alloy was rolled in three different conditions in order to understand the effects of the rolling conditions on the microstructure and mechanical ...properties. The sheet subjected to high temperature reheating at 500 °C for 5 min prior to each 100 °C rolling delivers the highest Index Erichsen (I.E.) value of 7.0 mm. The sheet rolled at 300 °C with 500 °C reheating for 5 min delivers the lowest I.E value of 5.4 mm, while the sheet continuously rolled at the same temperature shows a moderate I.E. value of 6.0 mm. Systematic observations of the microstructures of T4-treated and 3 mm stretched formed samples reveal that the large stretch formability of the sheet rolled at 100 °C with 500 °C reheating is associated the weak basal texture and fine-grained microstructure.
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Effects of alloying additions on deformation texture in Mg sheet alloys are still controversial. In this study, a quasi-in-situ electron backscatter diffraction method is used for the ...first time to monitor the texture evolution during the cold rolling process of Mg–Zn–Ca and Mg–Zn alloys. It is found that the Ca addition does not cause any texture weakening effect — it only delays the development of a strong basal texture by reducing the growth of deformation twins.
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Magnesium sheet alloy of dilute composition, Mg–0.3Zn–0.1Ca (at.%), does not exhibit any hardening response during heating. However, an annealing treatment at 80–200°C, after some ...plastic strain in tension, leads to a remarkable strengthening, rather than softening, effect. By using electron backscattered diffraction and scanning transmission electron microscopy, it is found that the strengthening effect is caused by the pinning of gliding basal dislocations by GP zones and possibly solute atoms segregated to the dislocations.
The sex pheromones of Ectropis grisescensWarren and Ectropis obliqua Prout were both reported to contain (Z,Z,Z)-3,6,9-octadecatriene (Z3,Z6,Z9-18:H) and (Z,Z)-3,9-cis-6,7-epoxy-octadecadiene ...(Z3,epo6,Z9-18:H). To clarify how these two sibling geometrids maintain premating isolation, the female sex pheromones of the two species were reexamined. Gas chromatography–electroantennographic detection (GC-EAD) and gas chromatography–mass spectrometry revealed two GC-EAD-active compounds, Z3,Z6,Z9-18:H and Z3,epo6,Z9-18:H, in E. grisescens female pheromone glands as well as an additional GC-EAD-active compound, (Z,Z)-3,9-cis-6,7-epoxy-nonadecadiene (Z3,epo6,Z9-19:H), in E. obliqua female pheromone glands. Synthesized Z3,Z6,Z9-18:H and Z3,epo6,Z9-18:H elicited dose-dependent electroantennogram (EAG) responses from male antennae of both E. grisescens and E. obliqua. However, Z3,epo6,Z9-19:H only elicited dose-dependent EAG responses from E. obliqua and limited EAG responses from E. grisescens at all doses. In wind-tunnel studies, lures that contained Z3,Z6,Z9-18:H and Z3,epo6,Z9-18:H attracted E. grisescens males and had no effect on E. obliqua males.The addition of Z3,epo6,Z9-19:H to the blend of Z3,Z6,Z9-18:H and Z3,epo6,Z9-18:H strongly attracted E. obliqua males but had a limited attraction for E. grisescens males. Thus, Z3,Z6,Z9-18:H and Z3,epo6,Z9-18:H were sex pheromone components of E. grisescens, whereas Z3,Z6,Z9-18:H, Z3,epo6,Z9-18:H and Z3,epo6,Z9-19:H were sex pheromone components of E. obliqua.The presence or absence of Z3,epo6,Z9-19:H played a central role in the premating isolation of these two sibling species.
Mg-3Al-1Zn (AZ31) alloy sheets with various thickness reductions from 10% to 60% were fabricated in a single pass at 150°C by hot-roller-cold-material rolling. The rolled sheets were then evaluated ...by microstructural characterization and tensile testing. The strength shows an increase with increasing thickness reduction from 10% to 40%, but the further increase in thickness reduction leads to a decrease in strength. Yield strengths of 273MPa along the rolling direction and 357MPa along the transverse direction are obtained for the sheet with 40% thickness reduction, which is characterized by highly elongated grains and high density dislocations, together with a few ultrafine, recrystallized grains in microstructure. The variation in strength with thickness reduction is discussed in light of the strengthening contributions from grain size and dislocation density.
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► Alloying effect of CaO on AZ91 alloy. ► The improved corrosion resistance with increasing CaO content. ► Corrosion barrier of Ca-containing precipitates. ► The formation of a more ...protective surface film.
Three types of AZ91 magnesium alloy with various weight percentages of calcium oxide ranging from 0 to 0.6 wt.% are examined using electrochemical techniques and surface analyses. The results show that AZ91 magnesium alloy has improved corrosion resistance with increasing calcium oxide content due to higher pitting potential and charge transfer resistance. In addition, the benefits of calcium oxide addition are the refinement of the precipitates and increased the formation of a more protective surface film in mixed Mg–Al–Zn–Ca oxides, resulting of the extra resistance between the a-Mg matrix and the second phase.
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