Boundary Precipitation Research Articles

Dynamic recrystallization behavior and strengthening mechanism of Mg–Gd–Y–Zn–Zr alloy during isothermal MDF process

As one of severe plastic deformation (SPD) methods, multi-directional forging (MDF) technology is an effective way to refine grains. The microstructure, texture evolution and mechanical properties of homogenized Mg–13Gd–4Y–2Zn–0.5Zr (wt. %) alloy during isothermal MDF process were synthetically investigated in the paper. The results showed that the mean grain size of the alloy decreased gradually with the MDF passes increased. After 4 passes, the average grain size of the alloy was refined to 2.7 μm, and the microstructure distribution was uniform. On the one hand, with the increasing of the MDF passes, the massive intergranular LPSO phases are gradually broken up and formed a deformation zone. The plate-like Mg5(Gd,Y) precipitates were located interior the grains. On the other hand, the spherical Mg5(Gd,Y) phases were randomly distributed with the increasing of MDF passes. In addition, the maximum texture intensity of the MDFed alloy on (0001) basal plane gradually was weaken from 15.993 of the 1MDFed alloy to 4.245 of the 4MDFed alloy, which was attributed to the increasing of volume fraction of dynamic recrystallized (DRXed) grains via MDF method. And the dynamic recrystallization (DRX) mechanisms were continuous DRX (CDRX), discontinuous DRX (DDRX), particle stimulated nucleation (PSN) and kink induced DRX. The maximum ultimate tensile strength (UTS) and tensile yield strength (TYS) after 4 passes were 385 MPa and 360 MPa respectively. The excellent mechanical properties of the alloy were owing to the grain boundary strengthening, dislocation strengthening, texture strengthening and precipitation strengthening. In addition, the second phase particles such as lamellar LPSO phases, broken block-shaped LPSO phases, spherical Mg5(Gd,Y) phases and plate-like Mg5(Gd,Y) phases were demonstrated to be the strengthening phases.

Solid-state alloying of Al-Mg alloys by accumulative roll-bonding: Microstructure and properties

In this study, a novel solid-state alloying approach was adopted to fabricate Al-Mg alloys with high Mg contents (CMg) by accumulative roll-bonding (ARB) of Al and Mg elemental materials to ultrahigh cycles. Experimental results showed that the degree of alloying increased with the increase of ARB cycles and a supersaturated α-Al solid solution accompanied with nanoprecipitates was formed in the Al-Mg alloys by ARB to 70 cycles. The as-prepared Al-Mg alloys exhibited enhanced mechanical properties, with a maximum tensile strength of ∼ 615 MPa and a tensile elongation of ∼ 10% at CMg = 13 wt.%. The high strength can be attributed to different mechanisms, namely solid solution strengthening, grain boundary strengthening, dislocation strengthening, and precipitation strengthening. The Al-Mg alloys showed increased work hardening with increasing CMg, due to the enhanced formation of nanoprecipitates. Meanwhile, no obvious drop in the intergranular corrosion (IGC) resistance was found in the Al-Mg alloys with CMg up to 13 wt.%. Moreover, sensitization treatment was found to induce little decrease in the IGC resistance of the Al-Mg alloys with CMg ≤13 wt.%. We found that the excellent IGC resistance was due to the suppression of grain boundary precipitation by the preferred formation of precipitates within the grains that were induced by ARB. Our study indicated the novelty of the present solid-state alloying approach to achieving a superior combination of high mechanical properties and IGC resistance in Al-Mg alloys.

Achieving superior strength and ductility in 7075 aluminum alloy through the design of multi-gradient nanostructure by ultrasonic surface rolling and aging

Aluminum alloys were used in various fields due to their high specific strength and low density. However, the disadvantage of low strength limits its wider application. In this work, the effect of ultrasonic surface rolling process (USRP) and artificial aging on microstructure and mechanical properties of 7075 aluminum alloy were investigated in detail. The results indicated that a multi-gradient nanostructure (MGNS) layer, i.e., grain gradient and precipitation gradient, was generated on the surface of the alloy. The tensile strength of the aged-USRP sample (692 MPa) was about 63 % higher than that of the coarse-grained sample (425 MPa), and the plasticity was comparable to that of the coarse-grained specimen. The underlying mechanisms of grain refinements, precipitation behavior and their effects on tensile properties were quantitatively analyzed. The high strength of the aged-USRP sample originated from grain boundary strengthening, precipitation strengthening, dislocation strengthening and synergistic strengthening. The activation of geometrically necessary dislocations (GNDs) during tensile deformation improved the plastic coordination ability of different microstructures. Thus, excellent strength-ductility synergy of 7075 aluminum alloy was obtained. • Multi-gradient nanostructure was formed on the surface of 7075 Aluminum Alloy. • Gradient nanostructure of type and number density of precipitates formed. • The multi-gradient nanostructure enhanced strength-ductility synergy of the alloy.

Microstructure evolution and compressive properties of a low carbon-low alloy steel processed by warm rolling and subsequent annealing

A low carbon-low alloy steel was processed by warm rolling with reductions range from ~30% to ~70% followed by annealing at 450°C. Then, the microstructural evolution was characterized by Field Emission Scanning Electron Microscopy (FE-SEM), Electron Backscatter Diffraction (EBSD), Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD) and compressive testing under strain rates of 1.0 × 10−3–2.0 × 103 s−1 was carried out. Microscopy analyses showed that ultrafine-grained structures with high-density dislocations and more and finer M3C carbides by comparison with the tempered steel were achieved after warm rolling. Subsequent annealing promoted the further precipitation of finer carbides and led to dislocation recovery as well as a slight coarsening of grains. Compressive testing results indicated that the yield strengths of the warm rolled steels at different strain rates were significantly increased by ~40–70% compared with the as-received sample, which was mainly attributed to a combination of dislocation strengthening, grain boundary strengthening and precipitation strengthening. After annealing, the yield strength decreased slightly due to a dislocation recovery and a slight increment of the grain sizes. In addition, the influence of microstructure evolutions including dislocation densities, grain sizes and carbide precipitations during warm rolling and subsequent annealing on the strain rate dependence of strength for steels was also analyzed.

Additive manufacturing of micro/nano multiphase synergistically reinforced Ti-55Al-7.5Nb with a reticular boundary precipitate via direct laser deposition

Additive manufacturing, with features of micro-area metallurgy and rapid solidification, has become an effective way to construct complex components with high efficiency and production flexibility. Hereby, this study presents a micro/nano multiphase synergistically reinforced Ti-55Al-7.5Nb/Ti 2 AlN-Ti 5 Si 3 metal–matrix composite (TiAl MMC) synthesized via direct laser deposition. The as-prepared TiAl MMCs exhibit homogeneously equiaxed grains and no cracks, compared with the coarse columnar microstructure and macro/micro cracks of Ti-55Al-7.5Nb alloy. The grain size of the TiAl MMCs increases in the form of a parabola with increase of the laser power, and also increases from the bottom to the top along the building direction with fixed laser power. Precipitates of Ti 2 AlN and Ti 5 Si 3 can alleviate the texture index, and thus facilitate an in situ production of isotropic MMCs. Meanwhile, TiAl MMCs feature excellent compressive and high-temperature (900 °C) tensile strength, resulting from the precipitates of rod-like Ti 2 AlN dispersed inside the grains, and the micro/nano-Ti 5 Si 3 reticularly distributed at the grain boundaries (GBs). The micro/nano multiphase reinforcement could help guide the additive manufacturing of preparing reticular-boundary-reinforced cracks-free TiAl MMCs, which feature controllable microstructures and enhanced mechanical properties. • Novel TiAl MMCs, prepared by in situ additive manufacturing, exhibit even equiaxed grains but no Al segregation or cracks. • Precipitates, the same orientation relationship with matrix, tune TiAl MMCs microstructures that show lower texture index. • The grain size of prepared TiAl MMCs varies with laser powers was revealed by a combination of experiment and simulation.

Phase-field model of grain boundary diffusion in nanocrystalline solids: Anisotropic fluctuations, anomalous diffusion, and precipitation

The anisotropic phase-filed model of grain boundary diffusion and precipitation of solute in nanocrystalline solids has been developed. In this model, the Cahn–Hilliard equation is generalized for the anisotropic phase-field diffusion of solute and anisotropic compositional fluctuations. It is found that dynamics of solute concentration profile demonstrates the anomalous diffusion behavior with scaling parameters depending on the mobility ratio and microstructure of a solid solution. It is noteworthy that the increase in source concentration can slow down the concentration front propagation due to uphill diffusion or formation of a new phase. Parameters of grain boundary diffusion control the precipitation dynamics. In particular, a decrease in transverse diffusion coefficient is responsible for longer incubation time, and lower rates of nucleation and nuclei growth in comparison with the case of isotropic solute transport near grain boundaries. Transport properties of boundary and bulk are responsible for the formation of the bimodal size distribution function of second phase particles and specific kinetics of average radius and number density.

Strengthening of cost-effective Co-free medium entropy alloys by Al/C alloying

The effects of the elemental Al or C addition on the microstructure and room-temperature mechanical properties of a cost-effective Cr12Fe60Mn16Ni12 medium-entropy alloy were investigated. The yield stress of a medium-entropy alloy substantially increased from 230 MPa to 458 MPa following the addition of small amounts of elemental Al (∼2.0 at.%) or C (∼1.0 at.%). Throughout experimentation and theoretical modeling, we were able to systematically show that the improvement in the yield stress following the Al/C addition was attributed to the combination of various strengthening mechanisms, such as grain boundary strengthening, precipitation strengtheing, and solid-solution strengthening mainly caused by the lattice distortion or lattice strain. On the fundamental level, this work provides insights into the effect of the lattice constant on the stress increase for both substitutional and interstitial solid-solution strengthening.

The Corrosive Improvement with High Temperature Laser Surface Treatment of AA7075

A recently developed AA7075 was subjected to solid solution, high temperature laser surface treatment and artificial aging. The microstructure evolution and precipitation behavior were examined, and their effects on corrosion behavior and corrosion cracking were analyzed. The results show that the coarse η phase disappears and many smaller η phases are formed after high temperature laser surface treatment. Most of the phases dissolved into Al matrix during solution, and fine η phases precipitated in laser treatment. The η′ phases were appeared in the high temperature laser surface treatment samples. It was concluded that reasonable laser scanning power owned the best corrosion resistance, lower intergranular corrosion tendency. Both lower laser scan power and higher scan power samples were susceptible to the intergranular corrosion, and the intergranular cracking was observed. In contrary, the reasonable sample which the laser power is 1000 W showed much better corrosion resistance due to the coarsening and separation of grain boundary precipitations.

Influence of silicide and texture on the room temperature deformation size effect of Ti65 alloy sheets/foils and its constitutive model modification

In micro-scaled plastic deformation process such as micro-forming, material size effect is challenging to investigate and reveal using traditional material models. Since high-temperature titanium alloys have become the critical materials of micro-parts depending on outstanding mechanical properties, studying the effect of texture and silicide precipitate on size effect in microtensile deformation of a high-temperature titanium alloy is of great significance because the size effect of highly alloyed titanium alloys has been less studied. In the present study, various heating treatments were performed to regulate grain size and texture and obtain silicide precipitate. The room temperature tensile tests were carried out to investigate the effect of the texture and silicide precipitate on the size effect of plastic deformation behaviour. It is revealed that silicide precipitation in the heat-treated specimens can lead to a more obvious “smaller is weaker” phenomenon and the specimens with transverse textures show a better strength–ductility match. In addition, considering solution strengthening, grain boundary strengthening and precipitation strengthening, the material constitutive model is modified by the effect of silicide and texture on the size effect, allowing for an accurate description of the tensile deformation characteristics at the microscopic scale. The results of the physical experiments and the hybrid constitutive model provide a basis for understanding and further exploration of the microscale plastic deformation behaviour of high-temperature titanium alloys.

Dependence of the global dayside reconnection rate on interplanetary magnetic field By and the earth’s dipole tilt

In the recent years, significant attention has been given to the combined effect of Interplanetary Magnetic Field (IMF) duskward component (By) and dipole tilt on the global magnetosphere-ionosphere system response. Numerous studies have pointed out that when the Earth’s magnetic dipole is tilted away from the Sun (negative dipole tilt during northern winter), and IMF has a positive By component, the effects on ionospheric currents, particle precipitation, ionospheric convection, and average size of the auroral oval, is significantly more enhanced, compared to when IMF By is negative. Furthermore, this IMF By polarity effect reverses when Earth’s dipole is tilted in the opposite direction. The underlying cause has remained unclear. Our analysis shows that substorms tend to be stronger during the same IMF By and dipole tilt polarity combination. Taken together with earlier results showing also more frequent substorms during the same conditions, our observations suggests that when IMF By and dipole tilt have opposite signs, there is a more efficient global dayside reconnection rate. We also show analysis of the occurrence frequency of periods of Steady Magnetospheric Convection, substorm onset latitude, and the isotropic boundary of proton precipitation, that are all consistent with our conclusion that the combination of IMF By and dipole tilt polarity affect the global dayside reconnection rate.

An Empirical Model of the Proton Isotropic Boundary (IB)

AbstractAt mid‐ and high‐latitudes, energetic protons of magnetospheric origin precipitate down to the upper atmosphere, manifested as one of the most important coupling processes between the ionosphere and magnetosphere. The equatorward boundary of the energetic proton precipitation, or called isotropic boundary (IB), is usually believed to coincide with the boundary in the magnetosphere where field line curvature scattering of protons transits from strong to weak. In this study, we statistically examine the global distribution of the IB for 39 and 115 keV ring current protons as detected by the NOAA/Polar Operational Environmental Satellites in 2013–2018 and propose an empirical model of the IB as a function of solar wind conditions, magnetic local time, and geomagnetic activity index. The IB is well ordered by SYM‐H index and interplanetary magnetic field Bz, moving to lower latitudes with more negative SYM‐H index and Bz values, and with larger AE index and solar wind pressure. Energy dispersions of the IB are also explored, consistent with the scenario of field curvature scattering in the magnetosphere. This empirical model can be used as an indirect measure of the strength of the magnetospheric stretching and may be applied in magnetosphere‐ionosphere mapping studies.

Grain size dependant high-temperature hot corrosion (HTHC) degradation behavior in Alloy 617 during exposure in Na2SO4 + NaCl + V2O5 salt mixture

In the present investigation, the implication of grain size on the high-temperature hot corrosion (HTHC) response in Alloy 617 is studied. Towards this, specific thermal and thermo-mechanical processing schedules were employed to attain a wide range of grain sizes (7–70 µm), while maintaining other microstructural features like Σ3 n (n ≤ 3) boundary fraction, retained strain, and precipitate fraction nearly at constant. Subsequently, these specimens were exposed to Na 2 SO 4 + NaCl + V 2 O 5 (75 wt% + 20 wt% + 5 wt%) salt mixture at 1273 K for 24 h. Post-corrosion analyses reveal the formation of a highly porous and thick oxide scale on the as-received (AR) specimen (~32 µm), a relatively less porous and non-uniform oxide scale on the very coarse-grained specimen (~70 µm), and a homogeneous and dense Cr-rich scale on the very fine-grained microstructure (~7 µm). Such a protective scale on the very fine-grained specimen, developed due to the enhanced diffusivity of Cr, obstructs the entry of corrodents and thereby minimizes the percolation depth (~60 µm). The percolation depth is relatively higher (~130 µm) in the very coarse-grained specimen due to the development of a porous and non-uniform oxide scale. However, its percolation depth is still lower than the AR specimen (~ 305 µm), because of the reduced grain boundary area available for the diffusion of the corrosive species into the substrate. The AR specimen has exhibited the maximum percolation depth due to the simultaneous presence of fine and coarse grains, leading to the failure of both the aforementioned resistive mechanisms i.e., the accelerated formation of a protective Cr-rich scale and lesser availability of diffusion paths for the ingression of the corrosive species. • Very fine and very coarse-grained microstructures are resistant to HTHC damage. • AR specimen with inhomogeneous grain size distribution underwent maximum damage. • Grain refinement accelerates Cr-oxide formation that blocks entry of corrodants. • Grain coarsening decreases the channels for ingression of corrodants into the alloy. • Inhomogeneous grain size distribution in AR fails to activate resistive mechanisms.

Strengthening of nanocrystalline Al using grain boundary solute additions: Effects of thermal annealing and ion irradiation

Strengthening of nanocrystalline Al by grain boundary solute additions was investigated for a series of dilute aluminum alloys, Al-Sc, Al-Sb, Al-Cr, and Al-W with grain sizes in the range of 50–200 nm. Thermal annealing of the alloys at low temperatures led to alloy softening, but with negligible change in the grain size. The reduction in strength can be attributed to the loss of solute in the grain boundaries arising from grain boundary diffusion and precipitation. Annealing at higher temperatures led to grain growth, but with little additional loss of strength, a result of precipitation hardening. The Al-Sc and Al-Sb alloys were additionally subjected to ion irradiation at various temperatures. These studies revealed that annealed samples regained their hardness due to solute redistribution by ion beam mixing. Alloy strength was independent of grain size between 50 and 150 nms. Irradiation-induced segregation of Sb to grain boundaries in Al-Sb further enhanced strengthening.

Determining Latitudinal Extent of Energetic Electron Precipitation Using MEPED On‐Board NOAA/POES

AbstractEnergetic Electron Precipitation (EEP) from the plasma sheet and the radiation belts ionizes the polar lower thermosphere and mesosphere. EEP increases the production of NOx and HOx, which will catalytically destroy ozone, an important element of atmospheric dynamics. Therefore, measurement of the latitudinal extent of the precipitation boundaries is important in quantifying the atmospheric effects of the Sun‐Earth interaction. This study uses measurements by the Medium Energy Proton Electron Detector (MEPED) of six NOAA/POES and EUMETSAT/METOP satellites from 2004 to 2014 to determine the latitudinal boundaries of EEP and their variability with geomagnetic activity and solar wind drivers. Variation of the boundaries for different electron energies and Magnetic Local Time (MLT) is studied. Regression analyses are applied to determine the best predictor variable based on solar wind parameters and geomagnetic indices. The highest correlation was found for the pressure‐corrected Dst index when applying a linear regression model. A model of the equatorward EEP boundary is developed separately for three different energy channels, >43, >114, and >292 keV, and for 3 hour MLT sectors. For >43 keV EEP, 80% of the equatorward boundaries predicted by the model are within ±2.2° cgmlat. The model exhibits a solar cycle bias where it systematically exaggerates the equatorward movement of the EEP region during solar minimum. The highest accuracy of the model is found in periods dominated by corotating interaction regions/high speed solar wind streams. The result will be a key element for constructing a model of EEP variability to be applied in atmosphere climate models.

A strong, ductile and in-plane tensile isotropic Mg-0.5Zn-0.5Y-0.15Si alloy

Strength ductility tradeoff, strain hardenability and in-plane isotropy under tensile loading are big dilemmas in magnesium alloys. In this study, we have fabricated an extruded low alloyed Mg-0.5Zn-0.5Y-0.15Si alloy. Based on bimodal grain size, strong basal texture, Schmidt factor analysis and precipitates (MgZn2, Mg3Zn6Y and Mg3Zn3Y2), the alloy exhibited high mechanical strength, high elongation to fracture, strain hardenability and excellent in-plane tensile isotropy. The underlying deformation mechanisms for excellent symmetric and high yield strength along extruded and transverse directions were synergistic effects of low Schmidt factor values of <a> basal slip due to intense basal texture (c-axes//ND), pre-induce dislocation, grain boundary strengthening and precipitate strengthening. While, the strain hardenability and high elongation to fracture are the combined effect of the interaction of <a> basal and profuse non-basal <c+a> dislocation with precipitates, dislocation pileup at grain boundaries, dislocation pileup on stacking faults and the signature of extension and contraction twinning activity.

Effects of solute atoms re-dissolution on precipitation behavior and mechanical properties of selective laser melted Al–Mg-Sc-Zr alloys

Selective laser melted (SLM) Al–Mg-Sc-Zr alloys still needs be post-treated to exhibit outstanding combination of strength and ductility. However, the influences of the different post heat treatments on the SLM Al–Mg-Sc-Zr alloys have not been systematically investigated. Hence, the SLM Al–Mg-Sc-Zr alloys were post-treated by a series of different heat treatments to investigate their influences on the SLM Al–Mg-Sc-Zr alloy, including the phase transitions, microstructural evolutions, and mechanical properties. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM) were used to study the emergence and effects of Al3(Sc,Zr) precipitates. Strengthening mechanisms of the different heat-treated samples were recognized and calculated in details based on the observations of cubic primary Al3(Sc,Zr) particles and spherical secondary Al3(Sc,Zr) precipitates behavior. Benefiting from the grain boundary strengthening and precipitation dispersion strengthening mechanisms, ultimate tensile strength of the aged samples increased from 353.7 MPa to 528.0 MPa.

Effect of cryogenic pre-deformation on the stress relaxation response and mechanical/corrosion properties in Al–Zn–Mg–Cu alloy

The stress relaxation ageing behavior and mechanical/corrosion properties of the alloys pre-treated by conventional T4 temper without pre-deformation and cryogenic pre-deformation with different levels (20%–80%) have been investigated and compared by hardness test, stress relaxation ageing test, tensile test, intergranular corrosion test and microstructure characterization. Pre-deformation by cryo-rolling could increase the steady-rate relaxation rate at 120 °C by 35%–360% and effectively prolong the duration of the variable-rate relaxation stage compared with the T4 treatment. The dislocation movement facilitated by the recovery is responsible for the significant increase in the stress relaxation rate. Increasing the pre-deformation level markedly improves the strength and localized corrosion resistance but lowers the elongation in the stress relaxation aged alloy. Cryogenic pre-deformation promotes the heterogeneous nucleation of relatively large η2-type phases at dislocations apart from the uniform formation of fine η2-type phases in the matrix. High density dislocations retain after stress relaxation ageing at the investigated temperature. The dislocation hardening could offset the softening due to the precipitate coarsening and leads to a higher strength in the alloy pre-deformed by 50–80%. The modified grain boundary precipitation consisting of narrower precipitation-free zones and discontinuous grain boundary precipitates contribute to the better corrosion resistance in the cryo-rolled alloy.

Future population transgress climatic risk boundaries of extreme temperature and precipitation

Anthropogenic climate change is influencing the frequencies of extreme weather events. Considering the adaptability to extreme climatic risks in the future, we focused on determining whether humans have been exposed to the risks before. We define the rim of two-dimensional histograms of population under 20-year extreme temperature and precipitation as a climatic risk boundary. More than 30% (16.3%) of world population in South Asia, sub-Saharan Africa, and other regions will transgress the climatic risk boundary by the end of this century under RCP8.5 (RCP2.6) scenario. While many areas with large cities will remain within the global climatic risk boundary, they will transgress their regional climatic risk boundaries. This study shows that it is also necessary to consider the limits to adaptation for each appropriate area, considering the cultural, technological, and social transferability of adaptation. This study will help refine public perceptions of extreme climatic risks and lead to more efficient policy making.

Tailoring Mechanical and Electrochemical Properties of the Cr15Fe20Co35Ni20Mo10 High-Entropy Alloy via the Competition between Recrystallization and Precipitation Processes

A strategy to improve the mechanical and electrochemical properties of Cr15Fe20Co35Ni20Mo10 (Mo10) high-entropy alloys (HEA) by regulating the thermal-mechanical process was investigated. Due to the mutual competition between recrystallization and μ-phase precipitation behavior, the microstructure after annealing consists of recrystallized fine face-centered cubic grains with numerous annealing twins, non-recrystallized deformed grains with high-density dislocations as well as high-density nanoscale μ-phase precipitates. The combination of grain boundary strengthening, precipitation strengthening, and hetero-deformation induced strengthening endowed an ultrahigh yield strength of 1189 MPa and a uniform elongation of 17.5%. The increased yield strength activated the formation of stacking faults and deformation twinning as the additional deformation modes, which enabled the Mo10 HEA to exhibit a high strain-hardening rate and thus maintained superior ductility and enhanced tensile strength. Most importantly, when high-density dislocations accumulate at the phase boundaries, the nanoscale μ-phase can plastically deform by dislocation slips and the formation of stacking faults, which can relieve the high stress concentrations and thus prevent the cracking. The electrochemical properties of the annealed Mo10 HEA are decreased (compared to the homogenized ones), but can be optimized by adjusting the content and size and fraction of the μ-phase. This work sheds light on developing high-performance HEAs.

A New Extruded Mg-6Bi-3Al-1Zn Alloy with Excellent Tensile Properties

Aiming to develop low-cost Mg alloys with good mechanical properties, a new Mg-6Bi-3Al-1Zn (wt.%, BAZ631) alloy having a high ultimate tensile strength of ~402 MPa and an elongation of ~15% was fabricated by single pass extrusion. The as-extruded BAZ631 alloy demonstrates an almost fully dynamic recrystallized microstructure with an average grain size of ~2.9 μm. Moreover, both nano-scale Mg3Bi2 and Mg17Al12 precipitates were found dispersed in the matrix. These excellent mechanical properties are attributed to the combined effects of grain boundary strengthening, dispersion and precipitation strengthening induced by both micro and nanoscale second phase particles, and solid-solution strengthening. This high strength and good ductile Mg-Bi based alloy without rare-earth elements addition is expected to inspire a new alloy design strategy for fabricating high performance Mg products for larger-scale industrial applications.