Long Period Stacking Ordered Phase Research Articles

Precursor H-induced pyrolysis towards hydrogen storage properties enhancement of Mg–Y–Zn alloys with diverse Y level

For advancing the hydrogen economy, developing Mg-based alloys for hydrogen storage is an important choice, in which the introduction of long period stacking ordered (LPSO) phase cracked it wide open. Presently, various contents of LPSO phase are obtained in Mg96-xY2+xZn2 (x = 0, 1 and 2) alloys by adjusting Y/Zn ratio. The formation of eutectic (Mg + Mg3Y2Zn3) in Mg96Y2Zn2 alloy and Y(Mg) solid solution in Mg94Y4Zn2 alloy both lead to a greater degree of element segregation, while Mg95Y3Zn2 alloy with only α-Mg and LPSO phase achieves relatively the most uniform element distribution. Hydrogen storage tests show that Mg96-xY2+xZn2 alloys can be activated only after one de/hydrogenation cycle and LPSO phase undergoes irreversible hydrogen-introduced decomposition, in-situ generating YH2/YH3 phases. Mg95Y3Zn2 alloy achieves the fastest kinetics and the highest hydrogenation capacity, ascribing to the most uniformly dispersed YH2/YH3 nanoparticles, the finest α-Mg grains and the most significant lattice constants. Mg95Y3Zn2 hydride exhibits the fastest dehydrogenation rate and lowest decomposition temperature owing to the “hydrogen pump” effect of the most dispersed YH2/YH3 phase. Further tests reveal that Mg95Y3Zn2 alloy has a good cycling stability for hydrogen absorption.

Microstructure and High-Temperature Mechanical Properties of Mg-1Al-12Y Alloy Containing LPSO Phase

This paper describes our study on the effect of the long-period stacking order (LPSO) phase on the comprehensive mechanical properties of the as-cast Mg-1Al-12Y (wt. %) alloy. The microstructure and tensile mechanical properties of as-cast alloy and solution treatment alloy were evaluated. The results showed that α-Mg matrix, Al2Y phase and β-Mg24Y5 phase were present in the as-cast alloy. After solution treatment, the β-Mg24Y5 phase in the alloy was dissolved and the LPSO phase was precipitated. The solution treatment did not cause grain growth or Al2Y phase change, but the comprehensive mechanical properties of the alloy were significantly improved. This was mainly due to the precipitation of the LPSO phase in the solid solution alloy. In addition, the dissolution of the β-Mg24Y5 phase after solution treatment could also improve the mechanical properties. The improvement of the comprehensive mechanical properties of solution treatment alloys at room temperature was due to the dispersion strengthening caused by the intragranular LPSO phase dispersed within the alloy, which had a good blocking effect on the movement of dislocations. The ductility of the solid-solution alloy was greatly improved at a high temperature while maintaining high strength because the LPSO phase is kinked, the dislocation density was reduced, and more non-basal slip was activated during the high-temperature tension.

Effect of Cu micro-alloying on the microstructure, mechanical and corrosion properties of Mg-Gd-Y-Zn based alloy applied as plugging tools

Dissolvable functional magnesium alloys are attracting strong attention due to the prominent advantages of high strength and suitable dissolution rate. Here, the effect of Cu micro-alloying (0, 0.4, 0.8 wt%) on the microstructure, mechanical and corrosion properties of Mg-9.5Gd-2.7Y-0.9Zn alloys are investigated. With the increase of Cu contents, the block 14 H long-period stacking ordered (LPSO) phase gradually increases, which promotes the nucleation of dynamic recrystallized (DRXed) grains. However, the migration of the sub-structure is inhibited caused by the plate LPSO phase and the growth of DRXed grains is suppressed. Eventually, the grain size of DRXed grains decreased. The alloy with 0.8 wt% Cu obtains higher yield strength compared with Cu-free alloys, which is mainly ascribed to multiple strengthening contributions containing second phase, dislocation, grain boundary and solid solution. Due to the potential difference between the LPSO phase and the Mg matrix in the investigated alloys, the LPSO phase acts as cathodic to accelerate corrosion. The 0.8Cu alloy exhibits the highest corrosion rate, which is the synergistic effect of the second phase (its larger volta potential compared with 0Cu and its higher fraction of LPSO phase), dislocation density, grain size and crystal orientation. Ultimately, the Mg-9.5Gd-2.7Y-0.9Zn-0.8Cu alloy exhibits an ultimate tensile strength of 380 MPa, tensile yield strength of 331 MPa, and decent corrosion rate (16.8 mg·cm−2·h−1 at 93 °C in 3 wt% KCl solution). This work strengthens understanding the Cu role in designing high-strength dissolvable Mg-RE alloys.

Effect of electrolyte systems on plasma electrolytic oxidation coatings characteristics on LPSO Mg-Gd-Y-Zn alloy

In order to solve the problem of poor corrosion resistance of Mg-Gd-Y-Zn alloy with high strength and high toughness. In this paper, two-step plasma electrolytic oxidation (PEO) was implemented on Mg-Gd-Y-Zn alloy with long period stacking ordered (LPSO) phase in seven different electrolyte systems. Optical microscope (OM), Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) were used to characterize the structure distribution and composition of the LPSO phase. X-ray diffraction (XRD), SEM, EDS, Mott-Schottky test (M-S), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and immersion hydrogen evolution were used to study the morphology, composition, structure and corrosion resistance of the PEO coatings prepared using the various electrolytes. The PEO coating prepared by the mixed electrolyte of sodium aluminate, sodium phosphate and sodium silicate, referred to as PEO-APS coating, had the most excellent structure and corrosion resistance. The coating was dense and uniform, the coating thickness was 3.5 μm, the open porosity was 4.4 %, the average pore size was 0.12 μm, and the corrosion current density icorr was 2.09 × 10−8 A cm−2. In addition, the formation mechanism and corrosion resistance mechanism of the PEO-APS coating were discussed, and the effect of LPSO phase on the PEO-APS coating was proposed.

Structural features of 18R-type long-period stacking ordered phase in Mg85Zn6Y9 alloy and the Ni doping effect on its hydrogen storage properties

Magnesium-based alloys with 18R-type long-period stacking ordered (LPSO) structures have attracted wide attention for structural and functional applications. To understand hydrogen storage properties of 18R phase, the Mg85Zn6Y9 alloy with 94 wt.% of 18R-type LPSO phase is prepared in this work. The 18R phase has a layered structure where Y-Zn-Mg and Mg layers alternately stack along the c-axis. In the Y-Zn-Mg layers, Y, Zn and partial Mg sites are co-occupied by Y and Mg, Zn and Mg, and Mg and Zn/Y atoms, respectively. Thus the 18R phase is easily decomposed into α-MgH2, γ-MgH2, YH2, YH3, C14-type Laves phase MgZn2 and minor CsCl-type Y(Mg,Zn) during ball milling under hydrogen atmosphere. After further hydrogen absorption-desorption cycling, Y(Mg,Zn) disappears gradually and C14 phase transforms into C15-type Laves phase. By contrast, the Mg85Zn6Y9 alloy has better hydrogen storage kinetics and cycle durability than pure Mg because of the catalytic effect of YH2/YH3 on hydrogen absorption-desorption and inhibition role of Laves phase in Mg crystallite growth. Moreover, the introduction of Ni into Mg85Zn6Y9 sample leads to a further decrease in activation energy of hydrogen desorption from 106.39 to 96.78 kJ mol−1 due to the formation of Mg2Ni. This work not only provides new insights into structural features and hydrogen storage characteristics of 18R phase but offers an effective method for improving hydrogen storage properties.

Dynamical, mechanical, anisotropic, and thermodynamic properties of Mg-XL-Y (XL = Zn, Al) alloys with long-period stacking ordered structures: A first-principles calculation

The dynamical, mechanical, anisotropic, and thermodynamic properties of Mg-XL-Y (XL = Zn, Al) alloys based on three long-period stacking ordered (LPSO) phases (ie, 10H, 14H, and 18R) have been investigated systematically by first-principles calculations. The LPSO phases of Mg-XL-Y (XL = Zn, Al) alloys are thermodynamically, dynamically, and mechanically stable. The each LPSO phase of Mg–Al–Y alloys has superior mechanical properties with larger resistances to deformation under applied stress and shear pressure, stiffness, as well as hardness than those of corresponding to LPSO phases of Mg–Zn–Y alloys. According to universal elastic anisotropic index, percent shear anisotropy, 3D surface structures of Young's moulus, and sound velocities, the LPSO phases of Mg-XL-Y (XL = Zn, Al) alloys exhibit obvious anisotropy. Besides, all LPSO phases of Mg-XL-Y (XL = Zn, Al) alloys possess low lattice thermal conductivity due to the strong anharmonicity. The calculated adsorption energies indicate that the 14H(001) surface of Mg–Al–Y system at the hollow site is more sensitive to absorb O atom.

Achieving ultra-high strength using densely ultra-fine LPSO phase

• An optimized FSP processing generates densely ultrafine LPSO blocks with an average width of ∼200 nm and an average length of ∼1 μm. • There is an ultrahigh strength up to approximately 800 MPa under the uniaxial compression of micropillars. • The strengthening effect by ultrafine LPSO blocks reaches approximately 630 MPa. Long period stacking ordered (LPSO) structures are an effective strengthening phase in Mg alloys. However, the coarse LPSO phases in as-cast alloys are very difficult to refine, and they dramatically reduce the strengthening effect. In the present study, friction stir processing (FSP) was employed to refine the structure of an Mg-12.8Y-4.7 Zn (wt%) alloy with a very high content of coarse LPSO phases. An optimized FSP regime refined the coarse LPSO phases into densely ultrafine blocks with an average width of ∼200 nm and an average length of ∼1 μm. An ultrahigh yield strength of ∼800 MPa was achieved under compression of the FSP region. Theoretical calculations indicated that the strengthening by the densely ultrafine LPSO phases was up to approximately 630 MPa.

Solid state recycling of Mg–Gd–Y–Zn–Zr alloy chips by isothermal sintering and equal channel angular pressing

The Mg-7Gd-4Y-2Zn-0.5Zr alloy chips were successfully recycled through isothermal sintering and equal channel angular pressing (ECAP). The mechanical properties and microstructure evolution of samples during the recycling process were studied in detail. The eutectic phases in the as-cast alloy transform into long period-stacking ordered (LPSO) phases after homogenization, which can improve the plasticity of the material. After isothermal sintering, the density of the sample is lower than that of the homogenized sample, and oxide films are formed adjacent to the bonding interface of the metal chips. Hence, the plasticity of the sintered sample is poor. Dense samples are fabricated after ECAP. Although the grains are not refined compared to the sintered sample, the microstructure becomes more uniform due to recrystallization. Fiber interdendritic LPSO phase and kinked 14H-LPSO phase are formed in the alloy due to the shear deformation during the ECAP process, which improves the strength and plasticity of the sample significantly. Furthermore, the basal texture is weakened due to the Bc route of the ECAP process, which can increase the Schmid factor of the basal slip system and improve the elongation of the sample. After 2 ECAP passes, the fully densified recycled billet shows superior mechanical properties with an ultimate tensile strength of 307.1 MPa and elongation of 11.1%.

Effect of extrusion parameters on microstructure, mechanical properties and damping capacities of Mg-Y-Zn-Zr alloy

In this work, different extrusion processes were carried out on a Mg-3.16Y-1.85Zn-0.37Zr (wt%) alloy containing long period stacking ordered (LPSO) phases. The effect of extrusion parameters on the microstructure, mechanical properties and damping capacities of the alloy were investigated. The results show that the alloy extruded at 360 °C and a ratio of 9:1 shows good comprehensive properties with a tensile yield strength (TYS) of 280 MPa, ultimate tensile strength (UTS) of 330 MPa, elongation (EL) to failure of 21% and damping value Q−1 of 0.023 (strain amplitude ε = 10−3) at room temperature (RT). As the extrusion temperature or ratio increases, the strength decreases and EL increases, while the damping value of ε = 10−3 at RT is slightly down due to the decrease in the LPSO phase and dislocation density. All as-extruded alloys show a similar variation tendency for the relationship between Q−1 and test temperature T, with elevated temperature (ET) damping capacities Q−1 > 0.01 at a frequency of 1 Hz and T > 300 °C. Strengthening mechanisms for mechanical properties of the as-extruded alloys have also been analyzed, and the damping capacities are also discussed in terms of the Granato-Lücke (G-L) dislocation theory and grain boundary sliding. The results of the present work provide a new perspective for further developing high-performance Mg-Y-based alloys with both high damping and excellent comprehensive mechanical properties by careful tailoring of the extrusion process parameters.

Nanoindentation on the Transformation of LPSO Phases during Different Solution Heat Treatments in an Mg-Dy-Nd-Zn-Zr Alloy

The objective of this study is the investigation of nanomechanical properties using nanoindentation of extruded and heat-treated Mg-Dy-Nd-Zn-Zr, with an emphasis on the transformation of long-period stacking-ordered (LPSO) phases. Solution heat treatment was performed with different heat treatment for durations on hot extruded Mg-Dy-Nd-Zn-Zr to monitor the transformation of LPSO phases, as well as to keep track of microstructural changes. The initial fine-grained microstructure, with blocky and lamellar LPSO structures within the matrix, first transformed into coarser grains with fewer LPSO lamellae, which then increased in amount again at higher annealing duration. The blocky LPSO phases, which have the highest hardness compared to the matrix grains with and without LPSO lamellae, consistently decrease in quantity, as so does the trend in their hardness value. The Mg matrix grains with LPSO lamellae show a lower hardness compared to the Mg matrix grains without or with a just few lamellar LPSO phases, and increase in quantity at long annealing durations. The overall hardness of the microstructure is essentially determined by the LPSO lamellae-containing grains and reaches a peak at 24 h. There is another peak found for the grain size values; however, this is at later annealing duration, at 72 h. The reduction in grain size towards longer annealing durations goes along with a reactivated formation of LPSO lamellae.

Tailoring the microstructural characteristic and improving the corrosion rate of Mg-Gd-Ni alloy by heat treatment with different volume fraction of LPSO phase

The microstructure and corrosion behaviors of Mg-Gd–Ni alloys with various long period stacking ordered (LPSO) phase volume fraction and heat treatments were investigated. Compared with as-cast alloys, the corrosion rates increased significantly after heat treatment, and increased with increasing volume fraction of LPSO phase, which may be due to the transformation of continuous bulk reticular LPSO phase to discontinuous rod-like and the precipitation of the lamellar 14 H LPSO phase, changing the corrosion propagation paths and providing more galvanic corrosion points for alloy with high LPSO phase volume fraction, resulting in corrosion rate of MgGd3Ni3 alloy increased significantly by 58.1%.

Kink-band formation in the directionally-solidified Mg/LPSO two-phase alloys

ABSTRACT The variation in the mechanical properties with the volume fraction of the long-period stacking ordered (LPSO) phase in directionally solidified (DS) Mg/LPSO two-phase alloys was examined. Unexpectedly, the yield stress of the DS alloys increases non-monotonically with an increase in the volume fraction of the LPSO phase. The LPSO phase is considered an effective strengthening phase in Mg alloys, when the stress is applied parallel to the growth direction. Nevertheless, the highest strength was obtained in alloys with 61–86 vol.% of the LPSO phase, which was considerably higher than that in the LPSO single-phase alloy. It was clarified that this complicated variation in the yield stress was generated from the change in the formation stress of kink bands, which varied with the thickness of the LPSO-phase grains. Furthermore, the coexistence of Mg in the LPSO phase alloy induced the homogeneous formation of kink bands in the alloys, leading to the enhancement of the ‘kink-band strengthening’. The results demonstrated that microstructural control is significantly important in Mg/LPSO two-phase alloys, in which both phases exhibit strong plastic anisotropy, to realize the maximum mechanical properties.

Phase equilibria of long-period stacking ordered phase in the ternary Mg-Y-Al alloys

• The 18R and 10H have been confirmed as the thermodynamically stable phases in Mg-Y-Al system. • The phase transformation of 18R→10H have been well determined. • The coexistence of 18R and 10H are observed by the atomic-scale resolution identification. • Three isothermal sections focusing on the LPSO phases was constructed by the experimental data. Phase equilibria focusing on the long-period stacking ordered (LPSO) phases have been experimentally investigated in the Mg-Y-Al alloys. The microstructures of the eleven representative alloys annealed at 450, 500 and 550 °C were systematically investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Two thermodynamically stable LPSO polytypes were identified, including 18R and 10H structures. Meanwhile, the transformation of 18R → 10H was detected in Mg-9.0Y-1.7Al (at.%) alloy, while the coexistence of 18R and 10H was observed in Mg-14.2Y-12.8Al (at.%) alloy. It was found that the LPSO phases were non-stoichiometric compounds with ternary solubilities. The 18R can dissolve up to 7.21 at.% - 8.37 at.% Al and 10.75 at.% -12.01 at.% Y, while the 10H can dissolve up to 9.35 at.%-10.37 at.% Al and 14.50 at.%-14.94 at.% Y. All of the experimental results were used to construct the isothermal sections, which is conducive to the design of Mg-Y-Al alloys.

A new insight into LPSO phase transformation and mechanical properties uniformity of large-scale Mg-Gd-Y-Zn-Zr alloy prepared by multi-pass friction stir processing

A large-scale fine-grained Mg-Gd-Y-Zn-Zr alloy plate with high strength and ductility was successfully prepared by multi-pass friction stir processing (MFSP) technology in this work. The structure of grains and long period stacking ordered (LPSO) phase were characterized, and the mechanical properties uniformity was investigated. Moreover, a quantitative relationship between the microstructure and tensile yield strength was established. The results showed that the grains in the processed zone (PZ) and interfacial zone (IZ) were refined from 50 µm to 3 µm and 4 µm, respectively, and numerous original LPSO phases were broken. In IZ, some block-shaped 18R LPSO phases were transformed into needle-like 14H LPSO phases due to stacking faults and the short-range diffusion of solute atoms. The severe shear deformation in the form of kinetic energy caused profuse stacking fault to be generated and move rapidly, greatly increasing the transformation rate of LPSO phase. After MFSP, the ultimate tensile strength, yield strength and elongation to failure of the large-scale plate were 367 MPa, 305 MPa and 18.0% respectively. Grain refinement and LPSO phase strengthening were the major strengthening mechanisms for the MFSP sample. In particularly, the strength of IZ was comparable to that of PZ because the strength contribution of the 14H LPSO phase offsets the lack of grain refinement strengthening in IZ. This result opposes the widely accepted notion that IZ is a weak region in MFSP-prepared large-scale fine-grained plate.

The Effects of Pre-Consolidation Heat Treatment on the Tensile and Fracture Toughness Behavior of the Rapidly Solidified Mg–Zn–Y–Al Alloys

This study is aimed to optimize the tensile properties and fracture toughness of rapidly solidified (RS) ribbon-consolidated Mg–0.85Zn–2.05Y–0.35Al (at%) alloys by changing the pre-consolidation heat-treatment temperature. The alloys prepared from RS ribbons heat-treated below 673 K consisting of bimodal α-Mg grains; coarse-worked grains (∼2.8 µm) with high Kernel average misorientation (KAM) values (∼1.8°), and ultrafine dynamically recrystallized (DRX) grains (∼0.68 µm) with intermediate KAM values (∼1.1°). The DRX grains involve cluster arranged layers (CALs) and thin plate-shaped long-period stacking ordered (LPSO) phase precipitation. The fine grain structure strengthens the alloy, significantly while they have little beneficial effects in retarding the crack propagation, thus resulting in low fracture toughness. The alloys that were heat-treated above 723 K prior to consolidation possessed a three kind of α-Mg grain structure; it consisted of fine DRX grains (∼2.3 µm) with low KAM values (∼0.5°) in addition to the coarse-worked grains and ultrafine DRX grains. The fine DRX grains improved strain hardening and ductility, resulting in fracture toughness increase. Furthermore, high-temperature pre-consolidation heat treatment produces block-shaped LPSO phase grains associated with α-Mg. This LPSO phase appears to work as an effective feature to toughen the materials, due to the frequent formation of microcracks in the phase and promotion of crack deflection.

Achieving high strength and rapid degradation in Mg-Gd-Ni alloys by regulating LPSO phase morphology combined with extrusion

In this study, Mg-13.2Gd-4.3Ni alloys containing continuous bulk-shaped long-period stacking ordered (LPSO), lamellar LPSO, and a small amount of eutectic phase were prepared, and the evolution of microstructure at different extrusion temperatures and its influence on mechanical and degradation properties as well as corrosion mechanism were investigated. Preheating before extrusion can effectively promote the precipitation of lamellar LPSO in matrix. EX400 with higher volume fraction of non-DRXed grains exhibited higher strength, which was mainly due to strong texture, high dislocation density, and high volume fraction of lamellar LPSO. The EX420 with higher volume fraction of DRXed grains showed higher degradation rate, which was mainly due to the higher density of grain boundary. The EX400 exhibited excellent comprehensive properties with tensile yield strength (TYS) of 334 MPa, ultimate tensile strength (UTS) of 484 MPa and elongation (EL) of 7.4%, ultimate compressive strength (UCS) of 638 MPa and compressive yield strength (CYS) of 443 MPa, degradation rate of 86.1 mg/cm2/h at 93 °C in 3 wt.% KCl solution.

High-Throughput Predictions of the Stabilities of Multi-Type Long-Period Stacking Ordered Structures in High-Performance Mg Alloys.

The effects of 44 types of elements on the stabilities of I1-constitute multi-type long-period stacking-ordered (LPSO) structures in Mg alloys, such as 4H, 6H, 8H, 9R, 12H, 15R, and 16H phases, are systematically investigated by first-principle high-performance calculations. The intrinsic stacking-fault energies (ISFEs) and their increments are calculated along with the formation enthalpies of solute atoms, and interaction energies between solute atoms and LPSO structures. The results suggest that the 15R phase is the easiest to form and stabilize among these LPSO structures, and 44 types of solute atoms have different segregation characteristics in these LPSO structures. A high temperature inhibits structural stabilizations of the LPSO phases, and these alloying elements, such as elements (Sb, Te, and Cs) for 4H; elements (S, Fe, Sb, and Te) for 6H, 8H, 9R, 15R, and 16H; and elements (S, Sb, and Te) for 12H, can effectively promote the stability of LPSO structures at high temperatures. S and Fe atoms are the most likely to promote the stabilities of the 16H structure with regard to other LPSO phases, but the Fe atom tends to inhibit the stabilities of 4H and 12H structures. This work can offer valuable references to further study and develop high-performance Mg alloys with multi-type LPSO structures.

An investigation of the deformation and cracking mechanism of Mg–1Al–12Y alloys based on in-situ SEM/EBSD slip trace analysis

In this work, the deformation mechanism and cracking behavior of Mg–1Al–12Y alloys with different contents of long-period stacking ordered (LPSO) phase during in-situ tensile testing at ambient temperature were investigated in detail using a scanning electron microscope (SEM) and electron backscatter diffraction (EBSD). The slip trace analysis results showed that the deformation of the three alloys was all dominated by dislocation slip and supplemented by extension twinning. The predominant slip deformation mode was basal <a> slip. The Mg–1Al–12Y alloy after solution treatment at 540 °C for 4 h (T4-4h) exhibited higher elongation due to greater non-basal slip activation (31.8%) and cross slip occurrence (10.4%) and lower twinning activity. This was primarily attributed to the fact that profuse lamellar LPSO phases in the matrix of T4-4h alloy promoted the activation of non-basal slip and inhibited the initiation of extension twins. In addition, crack nucleation of the three alloys was mainly concentrated at the grain boundaries and triple junction of the grain boundaries. Nucleation and crack propagation were mostly attributed to the surrounding grains with a hard orientation and the second phase at the grain boundaries, which was not conducive to coordinated deformation.

Unveiling initial oxidation behavior of Mg-Y-Zn long-period stacking ordered (LPSO) phase

The oxidation of long-period stacking ordered (LPSO) phase has received little attention. The present work reveals the inherent oxidation behavior of Mg-Y-Zn LPSO phase at initial stage through detailed microstructural analysis and thermodynamic calculations. At a relatively low temperature (350 oC), Y2O3 is the only oxidation product at the alloy surface, which shows a preferential nucleation and lateral growth behavior. Meanwhile, an underlying Mg-rich layer incorporated with Y-rich particles appears as a decomposition product of the LPSO phase. At a high temperature (500 oC), the long-range Y transport is dynamically suppressed by the thick Mg-rich shielding layer, prompting the preferential formation of MgO rather than Y2O3 at the growth front. The present study would contribute to the development of oxidation-resistant LPSO-containing Mg alloys.

Enhancing mechanical properties of Mg-Gd-Y-Zn alloys via microalloying with Ce and La

This study investigated the microstructure and mechanical properties of Mg-1Gd-1Y-1Zn (at.%) alloys containing designed amounts of Ce or La. The Mg&lt;sub&gt;5&lt;/sub&gt;(Gd,Zn) phase formed in the as-cast Mg-Gd-Y-Zn-Ce/La alloys and disappeared after a homogenization treatment at 500°C for 24 h. The addition of Ce and La resulted in the formation of Ce(Mg,Zn)&lt;sub&gt;12&lt;/sub&gt; and La(Mg,Zn)&lt;sub&gt;12&lt;/sub&gt; phases, respectively. Except for that, the Ce or La addition had no significant effect on the morphology, volume fraction, and type of the long-period stacking ordered (LPSO) phases in the Mg-Gd-Y-Zn alloy. The grain size decreased with increasing microalloying content because the heavy Ce and La atoms impeded atomic migration across the boundaries. The solute drag effect led to the formation of the rare earth texture in the extruded Mg-Gd-Y-Zn-Ce/La alloys, whose extent decreased with increasing microalloying content. The mechanical strength was improved by the addition of Ce or La at the sacrifice of ductility. In particular, La exhibited a stronger reinforcement ability than Ce when it was added to the Mg-Gd-Y-Zn alloys. Among the investigated chemical compositions, the Mg-1Gd-1Y-1Zn-0.3La alloy exhibited the highest strength because it had the finest grains, the highest volume fraction of the second phase, and the weakest texture intensity. Furthermore, the alloys showed an unusual yield asymmetry due to the difference in the deformation mode of the LPSO phase.