This study systematically examines the influence of Al content on the microstructure and tensile properties of extruded SEN (Mg–Al–Zn–Ca–Y) magnesium alloy sheets. Four alloys, SEN1, SEN3, SEN6, and SEN9, containing 1, 3, 6, and 9 wt.% Al, respectively, were investigated. In homogenized billets, grain refinement intensified with increasing Al content, which in turn promoted dynamic recrystallization (DRX) during extrusion. After extrusion, SEN1 and SEN3 exhibited partially recrystallized microstructures with unrecrystallized fractions of 7.3% and 3.5%, respectively, whereas SEN6 and SEN9 were fully recrystallized. The average DRX grain size increased from 8.4 μm in SEN1 to 17.7 μm in SEN6, followed by a slight decrease to 16.9 μm in SEN9, attributed to grain-boundary pinning by second-phase particles and discontinuous precipitates (DPs). With increasing Al content, the area fraction of second phases increased; all sheets contained fragmented second-phase bands aligned with the extrusion direction, while SEN9 additionally exhibited coarse β-phase particles and grain-boundary DPs. The evolution of yield strength with Al content was most strongly associated with the increased contribution of texture strengthening, together with additional contributions from solid-solution strengthening and particle strengthening at higher Al contents, particularly in SEN9. Strain-hardening analysis revealed that SEN6 exhibited the most sustained strain hardening and the greatest elongation. In contrast, SEN9 showed reduced ductility due to early particle-induced cracking associated with coarse β-phase particles. These results demonstrate that an intermediate Al content provides an optimal balance between strength and ductility in extruded SEN alloy sheets by promoting a fully recrystallized, homogeneous microstructure while avoiding coarse, undissolved secondary phases.

This study utilizes the CINEMA severe-accident analysis code, which is developed domestically, to analyze a multifailure accident scenario and verify the cooling performance of a PCCS for an i-SMR. Results show that stable cooling is maintained using the PCCS even under conditions of TLOFW combined with multiple failures. The cooling performances of the PCCS and for a scenario where the reactor vessel height is flooded up to 86% are compared. The results indicate that the PCCS offers superior cooling performance and higher heat-removal efficiency compared with the flooding method. Whereas this study utilizes assumed values based on the i-SMR concept, future analyses based on actual design values can provide a more precise verification of the cooling performance.

CAISER (CANDU Advanced Integrated SEveRe accident analysis) is the recently developed the system code to evaluate the severe accident of CANDU plant and models the CANDU reactor core, incorporating 380 fuel channels and 37 fuel pins within a Cartesian-coordinate node system. It enables detailed assessments of mass and temperature distributions inside fuel channels including core degradation and relocation. CAISER code is coupled with the reactor thermal-hydraulic module (MARS-KS), the ex-vessel containment module (CONTAIN) and source term module (SIRIUS) using dynamic linked libraries. Present study evaluated the reference scenario of severe accident from IAEA-CRP (TECDOC-1727), benchmarking severe accident simulation tools for CANDU applications. Calculated results by CAISER are compared with that of IAEA-CRP and MAAP-ISAAC v4.03 and are discussed from the in-calandria to the ex-calandria phenomena.

This study evaluates the corrosion behavior of high-pressure die-casting AZXW alloys, focusing on the influence of Al content (6, 9, 11, and 13 wt.%). The Al effect on corrosion resistance is characterized by a dual effect. The corrosion rates initially increase as Al content reaches 9 wt.%, which is attributed to a higher fraction of isolated β phases acting as micro-galvanic cathodes. Conversely, further increasing the Al content to 13 wt.% promotes the development of continuous network β phases, which serve as an efficient physical barrier that stops corrosion propagation. Furthermore, the Volta potential difference (VPD) between the α-Mg and β-phase decreases with rising Al concentrations, alleviating galvanic corrosion, further lowering the corrosion rate.

This study systematically investigates the effects of Al content on the microstructure, tensile properties, and high-cycle fatigue behavior of extruded Mg–xAl–Zn–Ca–Y (SENx) alloys. The results reveal that all extruded alloys exhibit fully recrystallized microstructures with undissolved second-phase particles enriched with Ca and Y. The average grain size varies non-monotonically with Al content due to the competing effects of recrystallization kinetics, solute drag, and particle band distribution. As Al content increases, tensile strength increases, while ductility decreases. Notably, despite its relatively coarse grain structure, the SEN9 alloy exhibits significantly higher yield strength than the SEN6 alloy. This improvement is mainly attributed to additional precipitation strengthening from fine Mg17Al12 discontinuous precipitates formed along grain boundaries. Meanwhile, the reduced elongation observed in the SEN9 and SEN11 alloys is attributed to premature fracture at coarse Mg17(Al,Zn,Ca)12 particle bands aligned along the extrusion direction. From the SEN1 to SEN9 alloys, the fatigue strength (FS) increases approximately linearly with ultimate tensile strength (UTS), reaching 170 MPa. However, this FS–UTS proportionality fails in the SEN11 alloy, where FS falls to 120 MPa despite the highest UTS. This deviation from the FS–UTS correlation that is observed for the lower-Al-content alloys is attributed to the clustered distribution of coarse Mg17(Al,Zn,Ca)12 particles in the SEN11 alloy, which promotes early crack initiation under cyclic loading. These findings emphasize the importance of controlled Al addition in enhancing both strength and fatigue resistance while also highlighting the adverse effects of excessive Al content owing to microstructural embrittlement.

Micro-alloying is an effective approach for improving the corrosion resistance of cast AZ91. However, the effect of micro-alloyed elements on corrosion resistance can be varied depending on the solidification rate influencing the diffusion and precipitation behavior of micro-alloying elements. This study investigated the effects of the cooling rate on the microstructure and corrosion behavior of micro-Ca and -Y alloyed cast AZ91 alloy (i.e., AZXW9100). To achieve various cooling rates, the alloys were prepared using three methods: steel mold casting (SMC), copper step mold casting (CSMC), and high-pressure die casting (HPDC). The corrosion behavior was analyzed through weight loss measurements, electrochemical impedance spectroscopy, and corrosion morphology observations. The results showed that the key microstructural factors influencing corrosion resistance differed between short- and long-term corrosion. As the cooling rate increased, the short-term corrosion rate was lowered from 0.91 mm/y (SMC) to 0.38 mm/y (HPDC), which was attributed to the decrease in the total area fractions of the eutectic α and β phases acting as galvanic corrosion sources. The long-term corrosion rate was reduced from 17.20 mm/y (SMC) to 0.71 mm/y (HPDC), which was revealed to be due to the enhanced connectivity of the β phase acting as corrosion barriers. Meanwhile, the increase in the cooling rate led to a modification of the Zn molar ratio in the β phase, reducing the Volta potential of the β phase from 101.8 mV to 66.9 mV. This reduction in the Volta potential of the main galvanic source also contributed to improved corrosion resistance. The HPDC AZXW9100 alloy produced in this study exhibited the lowest corrosion rate compared to other alloys. These findings suggest that controlling the cooling rate is a promising strategy for enhancing the corrosion resistance of AZXW9100 alloys.

Molecular dynamics simulations are performed to provide a detailed atomic-level understanding of the deformation and twinning behavior of single-crystal Mg nanopillars under [0001] and [011¯0] compressions. To that end, a new interatomic potential based on the second nearest-neighbor modified embedded-atom method is developed to improve the reproducibility of overall physical properties, particularly in relation to plastic deformation. Further nanopillar compression analysis reveals that the simulation based on the developed potential satisfactorily reproduces the experimentally observed slip and twinning phenomena, consistent with theoretical interpretations. The present simulation results provide visual evidence for differentiated deformation characteristics of single-crystal Mg in different loading orientations and for the detailed nucleation and growth mechanisms of the recently discovered unconventional twins known as “axial weak twins” that exhibit 90° and 62° orientation relationships with the parent matrix. Our investigation reveals that the formation of both weak twins is commonly associated with atomic shuffling in the high-stress state, and the nucleation of the 62° weak twin is facilitated by pyramidal I dislocations.

SBLOCA (Small Break Loss-of-Coolant Accident) severe accident scenario (RIH 2.5% break) with the moderator cooling system has been simulated. In addition to analyzing the thermal–hydraulic and core heat-up processes, we assessed the hydrogen generation from different parts within the core. Specifically, we evaluated the hydrogen generation resulting from the oxidation reaction in the feeder pipes using an Fe-steam oxidation reaction model. The high temperatures in the unbroken loop of the feeder pipes, caused by the convective heat transfer from hot steam within the fuel channels, facilitated the Fe-steam oxidation reaction. We analyzed the hydrogen generation rates and accumulated hydrogen mass for both the broken and unbroken loops. Furthermore, we observed that the Zr-steam oxidation reaction in the fuel channels and the Fe-steam oxidation reaction in the feeder pipes resulted in steam shortages within the feeder pipes. We accounted for this steam shortage by considering the partial pressure of steam, which influenced the oxidation reaction rate. The consideration of steam starvation reduces the total hydrogen generation mass from feeder pipes to about 40% compared to the results without accounting for steam starvation. Since the radiation view factor among the feeder pipes is uncertain due to their complex geometric configuration, we examined how changes in the radiation view factor affected hydrogen generation from the feeder pipes. An increase in the radiation view factor resulted in a more uniform temperature distribution among the feeder pipes, leading to an increased generation of hydrogen. Several crucial factors for future research were identified, including the consideration of end fittings and the potential for creep failure in the feeder pipes.

This review article provides overall understanding of stainless, environment-friendly, and nonflammable Mg alloys (SEN alloys) recently developed at the Korea Institute of Materials Science. SEN alloys are produced by adding small amounts of Ca and Y (each <1 wt%) into commercial Mg–Al based alloys, resulting in exceptional ignition and corrosion resistances and impressive mechanical properties. Their main advantages of SEN alloys are as follows. (1) A dense multi-oxide layer of SEN alloys comprising MgO, CaO, and Y2O3 impedes the outward dispersion of Mg vapor and the inward penetration of O2 during oxidation, thereby enhancing the oxidation and ignition resistances. (2) The presence of Ca- and Y-based second-phase particles in SEN alloys can enhance their corrosion resistance because Ca-containing particles prevent the spread of corrosion, and the replacement of Al-containing particles with less noble ones containing Y (e.g., Al–Mn–Y or Al–Y particles) retards corrosion. (3) The addition of minor amounts of Ca and Y renders excellent mechanical properties due to improved strengthening effects. These enhanced properties are attributed to more pronounced dynamic recrystallization and grain refining behaviors caused by the second-phase particles during extrusion. (4) Despite the presence of various types of second-phase particles, the fatigue properties of SEN9 alloys are similar to those of commercial AZ91 alloys. (5) Simultaneous introduction of Ca and Y suppresses the formation of Mg17Al12 discontinuous precipitates during aging, leading to the enhanced elongation of aged SEN alloys. (6) Adding mischmetal into the SEN9 alloy leads to a six-fold enhancement in extrudability. Consequently, the studies conducted on SEN alloys demonstrate their excellent ignition and corrosion resistances and mechanical properties, which broaden the industrial applications of Mg alloys by addressing their inherent weaknesses.

This study investigates the influence of extrusion conditions on the microstructure and tensile properties of Mg–6Al–0.3Mn–0.3Ca–0.2Y (SEN6) alloy, which is processed at various extrusion temperatures and ratios. An increase in both the extrusion temperature and ratio facilitates dynamic recrystallization during hot extrusion by enhancing thermal and strain energies, increasing the area fraction of recrystallized grains within the extruded material. As either the extrusion temperature or ratio increases, lattice rotation within the recrystallized grains intensifies, resulting in a stronger basal texture in the extruded material. During extrusion, the undissolved Al2Y, Al8Mn4Y, and Al2Ca particles within the billets are partially fragmented and realigned along the extrusion direction. However, the quantity, size, and dispersion of these particles are largely unaffected by variations in extrusion temperature and ratio. The tensile yield strength of the extruded material shows a positive correlation with increasing extrusion temperature and ratio, predominantly due to enhanced texture hardening. Specifically, the tensile yield strength of the material extruded at 400 °C with an extrusion ratio of 25 is 23.2 MPa higher than that of the material extruded at 300 °C with an extrusion ratio of 10. Despite the presence of non-recrystallized grains in materials extruded at the lower extrusion ratio of 10, compression and double twins form uniformly throughout the material during tension, as the widths of non-recrystallized grains are similar to those of recrystallized grains. Consequently, all extruded materials exhibit high tensile elongations, exceeding 20%.

The extrudability, microstructural characteristics, and tensile properties of the Mg-5Bi-3Al (BA53) alloy are investigated herein by comparing them with those of a commercial Mg-8Al-0.5 Zn (AZ80) alloy. When AZ80 is extruded at 400 degrees C, severe hot cracking occurs at exit speeds of 4.5 m/min or more. In contrast, BA53 is successfully extruded without any surface cracking at 400 degrees C and at high exit speeds of 21-40 m/min. When extruded at 3 m/min (AZ80-3) and 40 m/min (BA53-40), both AZ80 and BA53 exhibited completely recrystallized microstructures with a < 10-10 > basal texture. However, BA53-40 has a coarser grain structure owing to grain growth promoted by the high temperature in the deformation zone. AZ80-3 contains a continuous network of Mg17Al12 particles along the grain boundaries, which form via static precipitation during natural air-cooling after the material exits the extrusion die. BA53-40 contains coarse Mg3Bi2 particles aligned parallel to the extrusion direction along with numerous uniformly distributed fine Mg3Bi2 particles. AZ80-3 has higher tensile strength than BA53-40 because the relatively finer grains and larger number of solute atoms in AZ80-3 result in stronger grain-boundary and solid-solution hardening effects, respectively. Although BA53 is extruded at a high temperature and extrusion speed of 400 degrees C and 40 m/min, respectively, the extruded material has a high tensile yield strength of 188 MPa. This can be primarily attributed to the large particle hardening effect resulting from the numerous fine Mg3Bi2 particles. (c) 2021 Chongqing University. Publishing services provided by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Peer review under responsibility of Chongqing University

For load-bearing applications, biodegradable Mg alloys require high strength and slow degradation rates to support bone regeneration. This study proposes a design guide of Mg-Zn-Mn-Sr-Ca (ZMJX) alloys for load-bearing Mg implants using machine learning. To this end, it quantitatively investigates the correlation between 4 alloying elements with content of 0–3 wt%, ultimate compressive strength (UCS) and in vitro corrosion rate (CR) in ZMJX alloys. Cascade-forward neural networks predict UCS and CR with high accuracy of over 0.95 for a total of 840 data points. Random forest regression identifies Zn as a major determinant of UCS and CR. Based on this, three chemical compositions are recommended with improved compressive strength and in vitro corrosion resistance by well-verified neural network models. The proposed Mg alloys have UCS of 244–305 MPa and CR of 0.31–0.83 mm/y according to the change of the Zn content. These results can not only provide deep insights into ZMJX alloys, but also recommend a compositional window for load-bearing Mg implants.

As an integrated computer code development for severe accident sequence analysis in Korea, CINEMA has been developing from an initiation event to a containment failure. The CINEMA computer code is composed of CSPACE, SACAP, and SIRIUS, which are capable of simulating core melt progression with thermal hydraulic analysis of the RCS (reactor coolant system), severe accident analysis of the containment, and fission product analysis in the vessel and the containment, respectively. The severe accident progression in TMI unit 2 has been analyzed as a part of a validation of the CINEMA computer code. This analysis has been performed to validate CINEMA models on the core melt progression, in particular, RCS thermal hydraulic behavior during core melt progression, fuel cladding oxidation with hydrogen generation, and fuel melting with relocation to the lower part of the core. The CINEMA results on main parameters, such as RCS pressure and an integrated hydrogen generation mass are compared with the TMI-2 data. The CINEMA results have shown that the RCS pressure is very similar to the TMI-2 data. The CINEMA results and measured total hydrogen production are very similar, which were approximately 465 kg and 460 kg, respectively.

The commercial AZ91 alloy and nonflammable SEN9 (AZ91-0.3Ca-0.2Y, wt%) alloy are extruded at 300 degrees C and 400 degrees C. Their microstructure, tensile and compressive properties, and low-cycle fatigue (LCF) properties are investigated, with particular focus on the influence of the extrusion temperature. In the AZ91 and SEN9 materials extruded at 300 degrees C (300-materials), numerous fine Mg 17 Al 12 particles are inhomogeneously distributed owing to localized dynamic precipitation during extrusion, unlike those extruded at 400 degrees C (400-materials). These fine particles suppress the coarsening of recrystallized grains, decreasing the average grain size of 300-materials. Although the four extruded materials have considerably different microstructures, the difference in their tensile yield strengths is insignificant because strong grain-boundary hardening and precipitation hardening effects in 300-materials are offset almost completely by a strong texture hardening effect in 400-materials. However, owing to their finer grains and weaker texture, 300-materials have higher compressive yield strengths than 400-materials. During the LCF tests, {10-12} twinning is activated at lower stresses in 400-materials than in 300-materials. Because the fatigue damage accumulated per cycle is smaller in 400-materials, they have longer fatigue lives than those of 300-materials. A fatigue life prediction model for the investigated materials is established on the basis of the relationship between the total strain energy density ( 6.W t ) and the number of cycles to fatigue failure ( N f ), and it is expressed through a simple equation ( 6.W t = 10 center dot N f -0.59 ). This model enables fatigue life prediction of both the investigated alloys regardless of the extrusion temperature and strain amplitude. (c) 2022 Chongqing University. Publishing services provided by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ) Peer review under responsibility of Chongqing University

Mg–Al-based alloys with small amounts of Ca and Y, referred to as stainless, environment-friendly, nonflammable (SEN) alloys, exhibit significantly improved resistance to corrosion and ignition compared to commercial Mg alloys. This study investigates the microstructural characteristics and bending properties of extruded sheets of Mg–(9, 11)Al–1Zn–0.3Mn–0.3Ca–0.2Y alloys (SEN9 and SEN11). These sheets contain particles containing Ca or Y, such as Al2Y, Al2Ca, Al8Mn4Y, and Al–Ca–Zn phases, along with dynamically precipitated Mg17Al12 particles. In the SEN9 sheet, Mg17Al12 particles are distributed in a band-like pattern along the extrusion direction, whereas in the SEN11 sheet, a more uniform distribution of abundant Mg17Al12 particles is observed. In both sheets, a macrocrack initiates on the bottom surface of a specimen and propagates into the specimen at an angle of approximately 35° during three-point bending tests. The SEN11 sheet exhibits a higher bending yield strength (by 27%) than the SEN9 sheet, primarily due to the stronger grain-boundary and particle hardening effects in the former, resulting from finer grains and a greater number of particles. In the SEN9 sheet, sharp deformation twins and subsequent cracks along these twins are formed during bending. Meanwhile, in the SEN11 sheet, the numerous Mg17Al12 particles induce stress concentration during bending, ultimately leading to premature bending failure before the formation of twins. As a result, the SEN11 sheet exhibits a 59% lower bending formability compared to the SEN9 sheet.

This study investigates the microstructural characteristics, tensile properties, and high-cycle fatigue properties of a die-cast Mg–6Al–0.1Mn–0.1Zn–0.3Ca–0.2Y (SEN6) alloy with high corrosion and ignition resistances. The average grain size of an hourglass-shaped die-cast specimen of the SEN6 alloy is smaller at the surface region ( 7 μm) compared to the center region (12–15 μm) due to the higher cooling rate at the surface region. Four types of pores with different sizes and roundness features, namely, gas pores, island-shrinkage pores, gas-shrinkage pores, and net-shrinkage pores, are distributed throughout the specimen. The presence of small amounts of Ca and Y in the SEN6 alloy results in the formation of Al2Ca, Al8Mn4Y, and Al2Y particles. Coarse Mg17Al12 and Al2Ca particles are present along the grain boundaries, and relatively fine Al8Mn4Y and Al2Y particles are distributed inside the grains. The die-cast SEN6 alloy exhibits a tensile yield strength of 121.4 MPa, ultimate tensile strength (UTS) of 172.5 MPa, elongation of 5.1

In this study, the mechanical properties of as-extruded Mg-Al-Zn-Mn-Ca-Y alloys were quantitatively investigated with respect to alloying elements, extrusion temperature, microstructure and texture through interpretable machine learning (IML). To overcome the lack of data, two methods were devised to augment the existing dataset by 39 times using the mean and standard deviation of the measured data. Artificial neural networks predicted room-temperature tensile properties with an accuracy ranging from 0.842 to 0.997 based on R2 using 12 predictors for a total of 1179 data points. Shapley additive explanation identified that Al and Mn are the key determinants for strength and elongation, respectively. Partial dependence plots investigated the interaction of all features to understand the quantitative correlation between features. This IML approach revealed that texture, solid solution and secondary particles are related to the main strengthening mechanism of as-extruded Mg alloys. These results can provide insights into the utilization of IML approach to predict material properties and describe key variables for designing lightweight structural metals.

Effects of Al addition to a Mg–Bi binary alloy on its microstructural characteristics and tensile properties after extrusion are investigated via extrusion of Mg–3Bi–xAl (x = 0, 1, and 2 wt%) billets and analysis of the extruded materials. The Al addition negligibly affects the second-phase particles of the extruded alloy; however, an increase in the Al content causes significant decreases in the average grain size and maximum texture intensity of the extruded material owing to an increase in the area fraction of dynamically recrystallized (DRXed) grains. The Al addition improves the strength of the extruded alloy; this improvement is attributed to the enhanced grain-boundary hardening and solid-solution hardening effects induced by grain refinement and Al solute atoms, respectively. As the Al content increases from 0 wt% to 1 wt% and 2 wt%, the tensile elongation increases substantially from 2.8% to 9.4% and 16.9%, respectively. The reduction in the number and size of unDRXed grains with increasing Al content suppresses the formation and coalescence of cracks in the unDRXed grains during tension, which results in a significant improvement in the tensile ductility of the extruded material. During tensile deformation, large undesirable twins that act as crack initiation sites are locally formed in the unDRXed grains of the Mg–3Bi alloy, whereas relatively smaller twins are uniformly formed in both the DRXed and the unDRXed grains of the Mg–3Bi–2Al alloy. Consequently, the extruded Mg–3Bi–2Al alloy has a substantially higher tensile yield strength–elongation product (2924 MPa%) than the extruded Al-free B3 alloy (381 MPa%).