LPSO Phase Research Articles

Increasing the high-temperature mechanical properties of Mg-Gd-Y-Zn alloys by adding AlN/Al particles

The AlN particles reinforced Mg-10Gd-3Y-1Zn (GWZ) composites were prepared by mixing AlN/Al particles using ball milling followed by stirring casting method. The influence of AlN/Al particles on the microstructural evolution and high-temperature mechanical properties of GWZ alloys were revealed and discussed. With AlN/Al particles added into the as-cast alloys, the Mg3RE phase was transformed into lamellar LPSO phase, while the content of Al2RE and LPSO phase increased. Since the Al2RE and AlN were effective nucleation sites for α-Mg, the grain size of AlN/Al-GWZ composites was reduced obviously from 126.1 to 39.8 μm. After homogenization, due to the coherent lattice matching relationships between 18R-LPSO phase and Al2RE or AlN particles, the 18R-LPSO phase nucleated on the Al2RE and AlN particles. After ageing treatment, the 2AlN/Al-GWZ composite showed the optimum mechanical properties at 250 °C, with the yield strength, ultimate tensile strength and elongation of 247.1 MPa, 265.5 MPa and 4.0%, respectively. The strengthening effect was primarily originated from the AlN particles, Al2RE and LPSO phases in the 2AlN/Al-GWZ composite. Besides, the composites can achieve the enhancement of high-temperature strength without the sacrifice of plasticity due to the coordinated deformation of AlN particles as well as the refinement of grains.

Statistical analysis of the various LPSO phases in Mg97Zn1Y2 and Mg96.6Zn1Y2.2Zr0.2 alloys regulated by different heat treatments

Statistical analysis of the various LPSO phases in Mg97Zn1Y2 and Mg96.6Zn1Y2.2Zr0.2 alloys regulated by different heat treatments

Microstructure, deformation and fracture mechanism of Mg-Gd-Y-Zn-Zr alloy with different rolling routes during tension

The microstructure, deformation and fracture mechanism of unidirectional rolling (UR) and cross rolling (CR) Mg-4.7Gd-3.4Y-1.2Zn-0.5Zr alloy during tension were studied. Both rolled alloys exhibit typical bimodal microstructures, with the difference being that UR alloy has elongated grains containing rod LPSO phase, while CR alloy has relatively rounded deformed grains containing lamellar LPSO phase. After tension until fracture, the LPSO phase morphology of the two alloys remains unchanged. CR alloy exhibits a higher yield strength and lower elongation than UR alloy. Although the higher average basal <a> slip Schmid factor result in the lower yield strength of UR alloy, the activation of the high proportion of non-basal slip is responsible for its higher elongation. UR alloy and CR alloy exhibit ductile fracture and quasi cleavage fracture characteristics, respectively. For UR alloy, a variety of dislocations accumulated near grain boundary and the weak slip transfer effects between grains both contributes to the propagation of grain boundary cracks. However, the effects of weak interfacial bonding between metastable lamellar LPSO phase and matrix, along with the similar orientation and higher geometric compatibility of CR alloy, lead to the rapid spread of transgranular cracks.

Multimodal deep learning framework to predict strain localization of Mg/LPSO two-phase alloys

This study proposes a method for predicting three-dimensional (3D) local strain distribution under compressive deformation of as-cast Mg/LPSO two-phase alloys from 3D microstructure images. The 3D local strain distribution was obtained by applying the digital volume correlation method to X-ray CT images before and after compression tests. Three microstructure descriptors were extracted from the 3D microstructure images around each strain measurement point: volume fractions of the phases, persistent diagrams that can express the connectivity of the phases, and two-phase spatial correlation that can express the spatial distribution of the phases. A deep learning model was then constructed to predict local strain from the three microstructure descriptors. Since two types of descriptors were used in this study, numerical data and image data, multimodal deep learning was employed to make predictions. Thus, the use of multiple microstructure descriptors enabled predictions to be made with higher accuracy than when predictions were made from a single descriptor. Feature importance of the descriptors was assessed through correlation analysis and occlusion sensitivity analysis. The results revealed that high strain tended to occur in the region where the hard phase, LPSO phase, had a large elongated phase oriented at a 45° direction to the loading direction. This result is consistent with other previous studies and indicates that the proposed method is effective in elucidating the relationship between the microstructure and the deformation behavior of the material.

Implementation of Balanced Strength and Toughness of VW93A Rare-Earth Magnesium Alloy with Regulating the Overlapping Structure of Lamellar LPSO Phase and $$\beta^{\prime }$$ Phase

Implementation of Balanced Strength and Toughness of VW93A Rare-Earth Magnesium Alloy with Regulating the Overlapping Structure of Lamellar LPSO Phase and $$\beta^{\prime }$$ Phase

Enhanced mechanical properties of LPSOp/Mg composites using super high pressure treatment

The super high pressure (SHP) technique was employed to fabricate the magnesium matrix composites (MMCs) reinforced with long-period stacking order structure powder (LPSOp) by cubic-anvil large-volume press with six rams. The LPSOp was optimized through high energy ball milling (HEBM) with a chemical composition of Mg85Zn6Y9 (at%). The microstructure and mechanical properties of LPSOp/Mg composite was characterized by X-ray diffraction (XRD), scanning electron microscopy/transmission electron microscopy (SEM/EDS), transmission electron microscopy (TEM), microhardness and compressive tests. The microhardness of LPSOp exhibits a notable increase after HEBM, and the thermal stability of LPSOp is affirmed through elevated annealing. The SHPed LPSOp/Mg consists of Mg and LPSO phase. Upon annealing at 400 °C for 1 h, the LPSO phase precipitates from solid solution of Mg and W phase is also identified. The strength of composites by SHP treatment and subsequently annealing is significantly improved compared with the pure Mg without LPSOp, which demonstrates the maximum compression yield strength (CYS) of 250 MPa and ultimate compression strength (UCS) of 375 MPa with satisfactory ductility. The enhanced mechanical properties are attributed to the synergistic reinforcement effects of the dispersed and 3D skeletal structure of LPSOp with excellent interfacial bonding, the coexistence of nano-scale LPSO and W phase and partial solid solution strengthening.

Effect and mechanism of graphite addition on microstructures and hydrogen storage properties of Mg–Y–Zn alloy

In this work, the Mg-9.1Y-1.0Zn alloy are prepared by semi-continuous casting, and then mechanical milled with graphite. The microstructures and hydrogen storage properties of milled composite are systematically studied. The results show that the as-cast Mg-9.1Y-1.0Zn alloy exhibits serious agglomeration after milling. The addition of graphite significantly restrains the agglomeration of alloy and further refines the particles. Compared with as-cast Mg-9.1Y-1.0Zn alloy, the hydrogen storage properties of Mg-9.1Y-1.0Zn alloy milled with graphite is greatly improved. It needs only three times activation to be fully activated and its maximum hydrogen storage capacity is about 6.7 wt%. Besides, its dehydrogenation activation energy is decreased by about 40 kJ mol−1 relative to as-cast Mg-9.1Y-1.0Zn alloy. During hydrogen absorption and desorption, the stable YH2 hydride is generated by the disproportionation decomposition of LPSO phase. The graphite and in-situ formed YH2 present the synergistic confinement and catalysis effects on the milled Mg–Y–Zn alloy particles, which is conductive to the enhancment of hydrogen storage properties.

Thermo-mechanical processing characteristics and strain-rate-sensitive degradation properties of Mg-Er-Ni alloys

Hot deformation behavior, the corresponding microstructure evolution, and degradation properties of a weak-textured Mg-Er-Ni alloy containing a high-volume fraction of Ni-LPSO phases, have been investigated. Hot deformation behavior has been carried out in the temperatures range of 370 ∼ 460 °C and strain rates range of 0.001 ∼ 1 s−1. Flow stress-strain curves of high strain rate cases show a continuous increase trend without a steady or a peak stage, while that of low strain rate cases show an obvious dynamic softening after peak stress. Based on flow stress-strain curves, materials constants calculated by an Arrhenius-type constitutive equation, show a high n and Q compared to those of high-volume fraction α-Mg matrix Mg alloys. Optimal processing windows, based on the dynamic material model, is determined as high temperature domains. As for microstructure evolution, a complete recrystallization and dispersive Ni-LPSO fragments for high temperature & low strain rates while a restricted recrystallization and a streamline distribution LPSO phase for high temperature & high strain rates are observed. Varying degrees of continuous dynamic recrystallization, particle induced nucleation mechanism, as well as coordinated deformation of LPSO through kinking and bending account for the strain-rate-dependence hot deformation mechanism. As a result, dispersive Ni-LPSO fragments at low strain rates provide more degradation channels for the α-Mg matrix and thus possess better a degradation rate than the streamlined LPSO at high strain rates.

Mechanism of corrosion behavior induced by precipitates under plastic compressive stress in Mg-Gd-Y alloys

Through independently developed stress-loading equipment, stress corrosion tests on Mg-Gd-Y alloy were conducted in a 3.5 wt% NaCl solution. The effects of plastic compressive stress on the corrosion behavior of the alloy were thoroughly investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) among other microscopic analysis techniques. The results indicate that the alloy mainly consists of α-Mg grains, Mg24Y5 phase, Mg5Gd phase, and LPSO phase. The corrosion behavior of the Mg-Gd-Y alloy is significantly influenced by the microstructure of the interface between the precipitates and the matrix, the potential difference, and the stress state. In the unstressed state, the Mg24Y5 phase first induces corrosion at the edges of the α-Mg grain boundaries, which then spreads internally. Upon the application of plastic stress, the corrosion-inducing capability of the LPSO phase on α-Mg grains notably increases. This discovery provides new insights into the mechanisms by which plastic compressive stress affects the corrosion behavior of Mg-Gd-Y alloys and offers an important basis for the theoretical research and anti-corrosion design in the engineering applications of this alloy.

Interface structure of α-Mg/14H-LPSO: First-principles prediction and experimental study

The interfacial structure of the α-Mg/14H-LPSO phase in rare earth-including magnesium alloy was investigated via high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging and first-principles calculations of density-functional theory. Eleven possible interfacial models were constructed according to the different terminations of the LPSO phase, and the corresponding interfacial energies were calculated, from which the four most stable structures (Ter1-MgY-hollow, Ter2-Zn-hollow, Ter3-MgYII-hollow and Ter4-Mg-bridge) were obtained. The interfacial phase diagrams related to the Y chemical potentials were obtained from the calculations, and the most stable interfacial structure was evaluated. Ter1-MgY-hollow and Ter2-Zn-hollow have the lowest interfacial energies in the range of −0.7 eV < ΔμY < −0.6 eV, where fluctuating change of state is the minimized and the interface is the most stable. The separation work of the two models was calculated to predict the bonding strength of the structures at both ends of the interface. The calculation results show that the maximum interfacial separation work is 1.45 J/m2 for the interface model of α-Mg and 14H-LPSO phase structure with Ter2-Zn-hollow termination.

High Performance Mg Alloy with Designed Microstructure and Phases.

A high strength and ductile Mg-Gd-Y-Zn-Zr alloy was designed and fabricated. The local strain evolution of the alloys during plastic deformation was analyzed using high-resolution digital image correlation (DIC). The results showed that the β particles, nano-sized γ' phases, and LPSO phases were distributed in the as-extruded alloy and a bimodal microstructure was exhibited, including elongated un-dynamic recrystallized grains and fine dynamic recrystallized grains. With increasing extrusion ratio, the grain size remained, with the volume fraction of dynamic recrystallization of the as-extruded alloy increasing from 30% to 75%, and the as-extruded alloy exhibited a high strength-ductility synergy, which is attributed to the grain refinement, extensive β particles, and elongated block-shaped LPSO phases. The strain evolution analysis showed that a strain-transfer from un-DRXed regions to adjacent DRXed regions and LPSO phases can promote uniform plastic deformation, which tends to improve the ductility of the alloy.

High strength and high ductility Mg-Gd-Y-Zn-Zr alloys obtained by controlling texture and dynamic precipitation through LPSO phase structure of different initial morphologies

This paper investigated the effects of three different initial phase structures on the microstructure evolution and tensile properties of extruded Mg-Gd-Y-Zn-Zr alloy, using an extrusion ratio of 3.6. These three initial phase structures were obtained by heat treatment, which is narrow spacing long-period stacking ordered phase (LPSO) phase structure alloy (EN alloy), wide spacing LPSO phase structure alloy (EW alloy), and narrow spacing LPSO phase and β phase overlapping phase structure alloy (EO alloy). The dynamic recrystallization (DRX) and dynamic precipitation behavior of extruded alloys with different initial structures, as well as their strengthening and ductility mechanisms were studied in detail. After hot extrusion with a low extrusion ratio, the alloy exhibits a bimodal structure composed of undynamic recrystallization (UN-DRX) grains and dynamic recrystallization (DRX) grains with strong textures. The narrow-spacing LPSO phase structure inhibits DRX and dynamic precipitation, while both the wide-spacing LPSO phase structure and the overlapping phase structure alloys promote DRX and dynamic precipitation. The strength improvement is mainly due to the strong texture and internal dislocation pinning of the undynamic recrystallization zone (UN-DRX) and the high strengthening effect of the narrow spacing LPSO phase. Although the promotion of DRX improves grain boundary strengthening effect, it cannot make up for reducing the UN-DRXed grain strengthening effect. A lower volume fraction of β dynamic precipitation phase is beneficial for improving the ductility of the alloy.

Microstructure and mechanical properties of Tip/GWZ723 composites adjusted by Tip/Mg laminate structure

In this work, the spherical Tip was introduced into Mg-7Gd-2Y–3Zn (GWZ723) alloy, the Tip/Mg laminar-like configuration was constructed by hot extrusion. The layers quantity and interlayer spacing were adjusted by Tip content. The effects of Tip/Mg laminar-like structure parameters on the microstructure, mechanical properties, work hardening and fracture behavior of Tip/GWZ723 composites were investigated. The results indicate that after extrusion, the Tip elongates along the extrusion direction (ED) and form Tip/Mg laminar-like configuration with the matrix. The Tip aspect ratio increases with the Tip content increases, resulting in a pronounced Tip/Mg laminar-like configuration. The addition of Tip promotes DRX, refines the grain size and promotes the precipitation of the lamellar 14H LPSO phase. The Tip/Mg laminar-like configuration induces the accumulation of high-density dislocations at the interface, thereby contributing to hetero-deformation induced (HDI) hardening, which improves the work hardening rate and dynamic recovery rate. With increasing of Tip content, the HDI hardening effect becomes more pronounced. The Tip/Mg laminar-like configuration facilitates strain redistribution, alleviates stress concentration, impacts crack initiation and inhibits crack propagation, enhancing the plasticity of the Tip/GWZ723 composites. At a Tip content of 15 vol%, the 15 vol%Tip/GWZ723 composite exhibits YS of 439 MPa, UTS of 477 MPa and EL of 3.3 %.

Deformation mode and strengthening mechanism of Mg-Gd-Er-Zn-Zr alloy with different LPSO morphology

Figuring out the effects of LPSO morphology on the deformation mode and strengthening mechanism of Mg-RE alloys is helpful to improve their formability and mechanical properties. In this work, the Mg-8Gd-1Er-1Zn-0.6Zr (GEZ811) alloys with monolithic block LPSO (B-alloy) and lamellar LPSO (L-alloy) phase were respectively prepared by different heat treatment route. The effects of the monolithic LPSO morphology on deformation mode and strengthening mechanisms during high strain rate multidirectional forging (HSMDF) were analyzed. Results showed at the initial stage of HSMDF, twinning was the dominant deformation mode for B-alloy while non-basal slip was for L-alloy. With increasing forging pass, kink band of grains became primary for B-alloy, whereas kinking and breaking of the lamellar LPSO phase was dominant for L-alloy. The optimal UTS, YS and EL of the HSMDFed B-alloy and L-alloy at 12 P were 381.6 MPa, 324.1 MPa, and 8.8 %, and 358.4 MPa, 295.0 MPa, and 5.5 %, respectively. The difference in strength between B-alloy and L-alloy resulted primarily from the contribution of grain boundary strengthening and stacking fault strengthening, while the better plasticity of B-alloy was attributed to its lower deformation activation energy and the formed kink band of grains. Retaining the block LPSO phase as much as possible in the alloy before deformation is beneficial to enhancing the mechanical performance of Mg-RE alloys.

Creep deformation behavior and microstructure of α-Mg/long-period stacking ordered (LPSO) duplex Mg-Y-Zn alloy prepared by hot extrusion and heat treatment

There exists a great demand for improving the creep resistance of α-Mg/long-period stacking ordered (LPSO) duplex alloys. In this study, microstructure control through hot extrusion and heat treatment was employed on Mg-Y-Zn duplex alloys with the aim of achieving superior creep resistance. The extruded Mg-Y-Zn alloy exhibited an enhancement in the creep resistance with increasing heat treatment temperature. Furthermore, the heat-treated samples demonstrated outstanding creep resistance even under high stress. Their creep behavior is characterized by a low minimum creep rate and a relatively small stress exponent (n ∼ 5) even at high stress. Microstructural observations revealed that heat treatment induces grain coarsening and an increase in solute concentration within the recrystallized grains. Additionally, during creep deformation, a plate-like LPSO phase and kink bands formed within the recrystallized grains. Therefore, it is affirmed that the exceptional creep resistance observed in the Mg-Y-Zn alloys in this study can be attributed to the microstructure evolution induced by heat treatment and creep deformation.

Experimental study of low–cycle fatigue behavior in a Mg–Y–Zn alloy with initial LPSO phase

Asymmetric cyclic stress–controlled low–cycle fatigue (LCF) tests were performed on Mg–Y–Zn alloys with different initial long–period stacking–ordered structure (LPSO) phases at room temperature. The influences of the initial LPSO phase content on the LCF life of the tested alloys were investigated, and an improved Basquin model for predicting the LCF life was proposed, considering the influence of the initial LPSO phase content. The coupling effects of the LPSO phase content and morphology on the LCF behavior were studied through scanning electron microscopy (SEM) experiments on the fatigue fractures of three alloys. The results show that the hindrance degree of LPSO phase to fatigue cracks is affected by the morphology of LPSO phase and the relative position of the LPSO phase with respect to fatigue cracks. When fatigue cracks are perpendicular to the main LPSO phase surface, the hindering effect is more pronounced, and the hindrance degree of the LPSO with different morphologies to fatigue crack propagation predominantly follows this sequence: lamellar > granular > rod > block. When fatigue cracks are relatively parallel to the main LPSO phase surface, the hindrance degree of LPSO relative fatigue cracks with different shapes is mainly in the following order: granular > rod > lamellar > block. The variation of fatigue crack path through the LSPO phase is primarily due to the properties of the LSPO phase itself, followed by morphology and spatial relative position. In addition, under high-stress conditions, fatigue cracks primarily originate from the LPSO phase, whereas under low-stress conditions, fatigue cracks predominantly arise from the matrix. Consequently, the Mg–9Y-1.8Zn alloy exhibits the best fatigue performance under high-stress conditions with an approximate LPSO phase content of 23.7%. Meanwhile, the Mg–9Y–3.1Zn alloy, with an LPSO phase content of around 34.9% under low-stress conditions, demonstrates the best fatigue performance.

Study on the microstructure and mechanical properties of VW73B alloy at high extrusion ratio

The microstructure and mechanical characteristics of VW73B prepared by a high extrusion ratio (70:1) were studied. High-strength plastic VW73B alloy containing long-period structural phase (LPSO) was obtained by extrusion process. OM, SEM, TEM, and EBSD were used to investigate the relationship between microstructure and mechanical characteristics of VW73B. The findings indicate that VW73B presents complete dynamic recrystallization after deformation, and there are 14H-LPSO phases, SFs, and a large amount of β´ phase, which are precipitated after aging treatment. The UTS, YS, and EL of VW73B in peak aging state are 406 MPa, 339 MPa, and 9%, respectively. The β´ phase, LPSO phase, poor texture, and fine grain strengthening of VW73B contribute to its exceptional characteristics.

Effects of temperature-induced variation of the second phase on the microstructure, texture and properties of Mg-RE-Zn alloys

In this paper, the Mg-9.32Gd-3.72Y-1.68Zn-0.72Zr (wt%) alloy has undergone three times of repetitive upsetting extrusion deformation. Alloys with different morphologies and distribution patterns of the second phase have been prepared by varying the deformation temperature in each pass. The effects of the second phase on microstructure, texture and mechanical properties are investigated. The results show that (i) the second phase, including Mg5Gd and LPSO phase, has an important effect on the dynamic recrystallization (DRX) behavior of the alloy. (ii) Appropriate lamella distance and block phase size can promote the activation of the slip system and effectively weaken the texture strength. (iii) The DT sample has an effective combination of fine grain strengthening and second phase strengthening due to the reasonable second phase distribution and size, which greatly improves the UTS and YS of the alloy.

Effect of rotational-die ECAP parameters on microstructure and mechanical properties of Mg97Y2Zn alloys

In this work, the Mg97Y2Zn (at%) alloys have been processed by the rotary-die (RD) ECAP technique under different temperature or pass conditions to tailor the microstructure and mechanical properties. The results reveal that the DRX ratio (VDRX) increases with the increase of ECAP pass or temperature, weakening the texture intensity. The refinement of DRXed grains saturates after 9 passes of ECAP at 350 °C, while the size of DRXed grains (dDRX) monotonically decreases with the reduction of temperature from 400 °C to 300 °C in the case of the same pass number (9P). The combination of fine dDRX, large VDRX, and directionally arranged LPSO phases along the extrusion direction endows the 350 °C–9P alloy with the optimum strength and ductility synergy, exhibiting the tensile yield strength (TYS) of 267 MPa, ultimate tensile strength (UTS) of 318 MPa, and elongation of 10.3%. However, the larger VDRX, weaker texture, less low-angle grain boundaries combine to improve the elongation (14.7%) of the 400 °C–9P alloy at the expense of the TYS (231 MPa) and UTS (303 MPa). This paper provides useful information to optimize the RD-ECAP parameters for the fabrication of high-performance Mg97Y2Zn alloys.

High-Temperature Stability of Mg–1Al–12Y Alloy Containing LPSO Phase and Mechanism of Its Portevin–Le Chatelier (PLC) Effect

High-Temperature Stability of Mg–1Al–12Y Alloy Containing LPSO Phase and Mechanism of Its Portevin–Le Chatelier (PLC) Effect