Search

Dual-phase Mg-Li alloys sheets were rolled at four different temperatures ranging from liquid nitrogen to 300 °C to explore effect of rolling temperature on texture and mechanical properties of the material. Crystal plasticity simulation was utilized to illustrate the influence of slip activity on rolling texture development. The results show that the rolling texture is largely depended on deformation temperature. Unlike commercial Mg alloys, the critical resolved shear stress of basal slip in α-Mg phase of Mg-Li alloy decreased more significantly by increasing temperature compared to that of pyramidal slip. Enhancement of basal slip by increasing temperature triggered a decrease of split angle of basal poles for the double-peak texture. Prismatic slip largely enhanced by increasing temperature upon 200 °C, which induced a wider orientation spread along the transverse direction. For the β-Li phase, the promotion of {110}<111> slip system at elevated temperature triggered the enhancement of {211}<110> and {111}<211> texture components. The cryo-rolled sample exhibited the highest strength compared to the others due to a strong hardening behavior at this temperature. A two-stage hardening behavior was observed in these as-rolled dual-phase alloys. Strain transition at phase boundaries could be the reason for appearance of this two-stage hardening. [ABSTRACT FROM AUTHOR]

This study analyzed the microstructure and mechanical properties of a dual-phase Mg–Li alloy produced through submerged friction stir processing. The study focused on the recrystallization and grain refinement of distinct α-Mg and β-Li phases. Two methods were identified for refining the grains. The first method involved dynamic recrystallization in large deformed grains, resulting in recrystallized grains that had minimal impact on the two-phase distribution. The second method utilized a phase transition for the growth of new α-Mg and β-Li grains occurred through heterogeneous nucleation in the other phase. The relationship between the α-Mg and β-Li phases after the phase transition was observed to have an orientation of Mg[11–20]//Li[100], Mg(0–110)//Li(011). Maelstrom-affected zones were carefully observed near the advancing side, where severe recrystallization, phase transition, and second phase refinement occurred in this region. Submerged friction stir processing prevented grain growth due to a high density of phase boundaries and rapid heat dissipation. As a result, micro-nano grains were observed in the maelstrom-affected zone. The ductility of the interface was enhanced by the maelstrom-affected zone. Therefore, the maelstrom flow can improve mechanical performance through grain refinement and redistribution for dual-phase Mg–Li alloys during submerged friction stir processing. [ABSTRACT FROM AUTHOR]

Strain-induced phase transformation in a dual-phase Mg–Li alloy after a severe deformation has been investigated. β-Li phase was transformed into α-Mg phase as a consequence of large strain cold rolling. The morphology and density of the strain-induced phase could be controlled by slip activation in the β-Li phase. A multi-direction rolling procedure was designed to enhance phase transformation behavior. High density strain-induced phase refined phase structure and greatly promoted the yield strength of the material without a sacrificing the ductility. Strain-induced phase transformation is a potential method for improving the mechanical properties in dual-phase alloys. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Friction stir processing (FSP) was successfully performed on ultra-light dual-phase LZ91 Mg Li alloy, which provided a chance to study the microstructure and texture evolution of this alloy during severe plastic deformation. The results showed that LZ91 Mg Li alloy could be processed successfully with 200–400 rpm, 25 mm/min, and water cooling during FSP. No defects were observed on the surface and in the cross-section. The microstructure was strongly influenced by the material flow modes during FSP. Two greatly phase refinement regions were found in the stir zone where the α-Mg and β-Li phases were refined to submicron scale and homogeneously mixed. Maelstrom currents flow between two threads on the pin triggered this phase fragment. The high rotation rate of FSP leads to a remarkable recrystallization and grain growth due to the high heat input. The severe plastic deformation caused a phase transformation inside the refined α-Mg phase. The new phases enriched Li element exhibited a coherent relationship with the matrix. It shows that FSP promoted the short-term diffusion in refined α-Mg. • Two phases in dual-phase Mg Li alloy were refined to submicron scale and distributed evenly after FSP. • Materials flow modes strongly influenced the grain refinement and phase distribution in FSPed Mg Li alloy. • A phase transformation inside refined α-Mg phase was discovered and analyzed. [ABSTRACT FROM AUTHOR]

Twinning was regarded as an effective way to modify the precipitation in Mg alloys. Two procedures were designed to illustrate twinning-aging consequence on Mg 17 Al 12 phase evolution. The effect of multiple steps of twinning-precipitation on the morphology and density of the continuous precipitates inside the twins and the matrix were comprehensively analyzed through phase-orientation related observation. The results show the shape of precipitates in twins was similar to that in the matrix as the CPs mostly lay on the basal planes with an asymmetric-lozenges shape. The CPs were remarkably refined and its density became much higher inside twins. Moreover, the aspect ratio of the CP plates in twins was around 45% of that in the matrix, which means the CPs inside twins became more globular. The precipitation behavior of Mg 17 Al 12 phase inside double extension twins was different from the primary twin or the matrix. The Mg 17 Al 12 phases lay on both basal and prismatic planes can be observed in double twins of two-step precipitation. The growth behavior of pre-precipitates in twins is different from those in the matrix. The growth rate along its thickness became higher than that in the matrix, which is probably related to dislocation-assisted diffusion at the basal plane. • Morphology of CPs precipitated in the matrix, primary and double twins is different • Ratio of length and thickness of CPs in twins significantly decreased • CPs lay on basal and prismatic planes are prepared in one twin structure • Dimension of CPs precisely characterized by phase-orientation related observation [ABSTRACT FROM AUTHOR]

AA2099 Al-Cu-Li alloys were rolled by both asymmetrical and conventional rolling to a total thickness reduction of 80% at room temperature. Microstructure and texture evolution through thickness of rolling sheets were comprehensively investigated. Results show that large shear stress in ASR sample gave rise to a distortion of grain structure and a remarkable work hardening at region close to fast rolled surface. Shear banding behavior was largely promoted by ASR and various types of shear bands with higher density were observed. The shear bands triggered a kink of grain structure during rolling process. The kink behavior was related to the tilt angle and width of shear bands. The shear bands exhibited large tilt angle and width gave rise to a more significant kink of the grain structure nearby. Recrystallization during subsequent annealing was also promoted by ASR. Shear bands became favorable nucleation sites for rolled material. Growth advantage of some nuclei inside shear bands had a stronger influence on the recrystallized texture in AA2099 rolled sheets. • Asymmetrical rolling brought inhomogeneous microstructure and texture through thickness. • Grain structure was kinked into several parts due to formation of shear band. • Kink behavior is depended on the direction and the width of shear bands. • Shear banding nucleation triggers uncommon recrystallized texture during annealing. [ABSTRACT FROM AUTHOR]

• Nanocrystalline structure was produced by cryogenic rolling in an AA 2099 alloy. • Ultrafine structure was observed inside or near the regulate-oriented shear bands. • Severely deformation and related temperature increase leads to the grain refinement. • Shear banding was promoted due to strong work hardening at cryogenic temperature. Solid solution treated AA 2099 alloy was rolled by a total reduction of 80% at both room and cryogenic temperature. Results show that nanocrystalline grain structure with a size around 20–100 nm was only observed in the cryogenic temperature rolled sample at high rolling strain. The formation of those nanograins related to shear banding behavior. Shear banding behavior was greatly promoted by cryogenic temperature rolling, which had a strong influence on mechanical homogeneity of rolled samples. The width of these high-density shear bands is around 0.2–8 µm. Shear strain partitioning between slip and shear banding was depended on slip behavior in deformed grains. Strain concentration inside shear bands may give rise to an obvious temperature increase, which caused significant grain refinement in or near the shear bands. The growth of nano-grains is retarded due to limited heat and pinning effect of nanosized precipitation. [ABSTRACT FROM AUTHOR]

Microstructure evolution of severely cold rolled dual-phase Mg–Li alloy during annealing at various temperatures was systemically investigated. The results showed that severely deformed α-Mg phase can be significantly refined by annealing process. α-Mg phases were first stratified into various layers by phase transformation from α-Mg phase into β-Li phase. Low angle grain boundary was more easily inducing phase transformation compared to high angle one during annealing. α layers continuously broken into chains of α grains at high annealing temperature, which is controlled by the motion of triple junction at the intersection of phase and grain boundary. Grain boundaries exhibited a high interface tension compared to phase boundary, which drove the globularization of α-Mg grains. Mechanical properties and strain hardening behavior were influenced by phase refinement. Coordination of grain refinement and phase refinement promoted the ductility of dual-phase Mg–Li alloy without a remarkable decrease in strength. [ABSTRACT FROM AUTHOR]

Microstructure and texture evolution of Mg-8.8 wt%Li-0.8 wt%Zn dual-phase alloy during cold rolling to 70% thickness reduction were investigated. The results showed that both α-fiber and γ-fiber of β-Li phase were enhanced during the cold rolling procedure and {001}<110> was the dominant texture component. A double-peak texture with a large tilt angle of 28° was observed in α-Mg phase. Each peak of this texture component exhibited a wider orientation spread towards the transverse direction. This spread is related to the strong activation of pyramidal II slip. Basal slip was still the dominant slip mode and the activities of pyramidal I and pyramidal II slip were also largely enhanced. Schmid factor analysis and viscoplasitc self-consistent simulation jointly suggests that the development of the rolling texture in α-Mg phase can be ascribed to the competition between basal slip and pyramidal slip. • Second order pyramidal slip was promoted in the dual-phase structure Mg–Li alloy. • Pyramidal II slip has a stronger impact on texture compared to pyramidal I slip. • Two stable rolling texture components were found in the α-phase. • Competition of basal and pyramidal slip has a strong impact on texture development. [ABSTRACT FROM AUTHOR]