The effects of 1Zn and/or 2Ag additions on the hot tearing susceptibility (HTS) of Mg-14Gd-0.4Zr (wt%) alloy were studied. The HTS was evaluated by both theoretical predictions using Kou's criterion and experimental observations based on the in situ force-temperature recorded constrained rod casting (ISFTCRC) method. The results show that the order of HTS from high to low is Mg-14Gd-2Ag-1Zn-0.4Zr, Mg-14Gd-2Ag-0.4Zr, Mg-14Gd-1Zn-0.4Zr and Mg-14Gd-0.4Zr. Adding 1Zn and/or 2Ag changes the solidification path and the solidification interval, which affects the hot tearing susceptibility. Alloying elemental 1Zn slightly increases the solidification interval and the temperature range in the square root of the solid phase fraction (f(s)(1/2)) range of 0.949-0.995, resulting in a slight increase in the hot tearing susceptibility. The addition of 2Ag drastically widens both the solidification interval and the temperature range in the f(s)(1/2) range of 0.949-0.995, thus significantly increasing the hot tearing susceptibility. Compared to the addition of 2Ag alone, the broadening degree of both the solidification interval and the temperature range in the f(s)(1/2) range of 0.949-0.995 is greater by adding the composite 2Ag/1Zn, which further promotes the occurrence of hot tearing. A narrower solidification interval and a temperature range in the f(s)(1/2) range of 0.949-0.995 result in a lower hot tearing susceptibility. (c) 2024 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

This research meticulously investigates the effects of varying contents of Nd and Gd, along with various heat treatment conditions, on the microstructure and mechanical characteristics of Mg-4Y-Nd-Gd-0.4Zr (wt.%) alloys within the commercial WE43 series, aiming to enhance mechanical performance while minimizing production costs. Findings reveal that Mg-4Y-1Nd-2Gd-0.4Zr alloy exhibits superior mechanical performances after undergoing a solution treatment at 500 °C for 14 h followed by peak-ageing at 200 °C for 120 h. Specifically, the ultimate tensile strength of 342.1±4.9 MPa for the peak-aged Mg-4Y-1Nd-2Gd-0.4Zr alloy exceeds those of Mg-Y series alloys previously reported. The contribution of grain boundary, solid solution and precipitation strengthening is calculated to be 26.2 %, 17.3 %, and 56.5 % of actual yield strength in the peak-aged Mg-4Y-1Nd-2Gd-0.4Zr alloy, respectively, indicating that the precipitates β' have an ascertainable influence on the yield strength. During deformation the basal slips could be effectively arrested by the prismatic β' precipitates, leading to the augmentation of mechanical performance.

In order to improve the ductility of commercial WE43 alloy and reduce its cost, a Mg-3Y-2Gd-1Nd-0.4Zr alloy with a low amount of rare earths was developed and prepared by sand casting with a differential pressure casting system. Its microstructure, mechanical properties and fracture behaviors in the as-cast, solution-treated and as-aged states were evaluated. It is found that the aged alloy exhibited excellent comprehensive mechanical properties owing to the fine dense plate-shaped β' precipitates formed on prismatic habits during aging at 200 °C for 192 hrs after solution-treated at 500 °C for 24 hrs. Its ultimate tensile strength, yield strength, and elongation at ambient temperature reach to 319 ± 10 MPa, 202 ± 2 MPa and 8.7 ± 0.3% as well as 230 ± 4 MPa, 155 ± 1 MPa and 16.0 ± 0.5% at 250 °C. The fracture mode of as-aged alloy was transferred from cleavage at room temperature to quasi-cleavage and ductile fracture at the test temperature 300 °C. The properties of large-scale components fabricated using the developed Mg-3Y-2Gd-1Nd-0.4Zr alloy are better than those of commercial WE43 alloy, suggesting that the new developed alloy is a good candidate to fabricate the large complex thin-walled components.

In this study, a high-performance Mg-3Nd-3Gd-0.2Zn-0.5Zr alloy is prepared. The precipitate microstructures of the studied alloy during isothermal aging at 225 degrees C are characterized by HAADF-STEM observations, and the corresponding mechanical properties are also investigated. It is noted that the evolution of the precipitate microstructure is mainly divided into three stages: the precipitation and growth of 0 '', the transition from 0 '' to 01, and the ripening of 01. There are apparent differences in the mechanical properties of alloy in these three stages. At the beginning of aging treatment, due to the precipitation and growth of 0 '', the yield strength of alloy in-creases rapidly while the elongation decreases. Afterwards, the transition of precipitates from 0 '' to 01 leads to the simultaneous increment in the yield strength and elongation of the alloy. Finally, as the 01 precipitates ripen, the yield strength of the alloy decreases while its elongation shows a trend of increment owing to the significantly improved dimensions and reduced number density.

建立了可控冷却速率的实验方法、凝固过程测温方案和合金内部温度推算方法,对Mg-6Gd-3Y-0.5Zr(质量分数,％)(GW63K)合金开展可控冷却速率实验,结合X射线断层扫描技术、扫描电子显微镜和X射线能谱分析等实验表征手段,表征可控冷速镁合金的凝固组织形貌并获取定量信息,研究了冷却速率对GW63K合金凝固组织微观形貌、定量信息的影响和变化规律.结果表明:在GW63K合金凝固组织中,共晶呈网络状分布在晶界处,形状不规则的第二相呈岛状分布在共晶组织中;平均冷却速率Rc在0.13～0.33℃/s范围内,随着冷却速率的增加,网状共晶组织更密集、均匀和连续,第二相分布更均匀、尺寸更小,微观溶质偏析减小,第二相和共晶体积分数均呈下降趋势.

This work investigated the effects of different Y additions (0, 1.5, 3.0 and 4.5 wt.%) on the microstructural evolution and mechanical performance of cast Mg-3Nd-0.2Zn-0.5Zr alloy. The results show that as the Y content increases, the key secondary phases in as-cast alloys change from the Mg12Nd type to the Mg24Y5 type. Meanwhile, the number density of Zn-Zr particles in the grains of as-quenched alloys gradually decreases. HAADF-STEM observations of peak-aged samples reveal that element Y is greatly enriched in the globular β′ precipitates, leading to a significantly increased volume fraction and promoted precipitation kinetics of β′ precipitates, resulting in enhanced strength of the alloy. Tensile tests reveal that, with the addition of 4.5 wt.% Y, the yield strength of the base alloy is substantially increased by 88 and 61 MPa after being aged at 200 and 225 °C under peak-aged conditions, respectively.

The microstructure, aging behavior and mechanical properties of cast Mg–3Nd–3Gd–xZn–0.5Zr (x = 0, 0.5, 0.8, 1 wt%) alloys are investigated in this work. Zn–Zr particles with different morphologies form during solution treatment due to the additions of Zn. As the Zn content increases, the number density of Zn–Zr particles also increases. Microstructural comparisons of peak-aged studied alloys indicate that varying Zn additions could profoundly influence the competitive precipitation behavior. In the peak-aged Zn-free alloy, β′′ phases are the key strengthening precipitates. When 0.5 wt% Zn is added, besides β′′ precipitates, additional fine β1 precipitates form. With the addition of 0.8 wt% Zn, the peak-aged 0.8Zn alloy is characterized by predominantly prismatic β1 and scanty basal precipitate distributions. The enhanced precipitation of β1 should be primarily attributable to the presence of increased Zn–Zr dispersoids. When Zn content further increases to 1 wt%, the precipitation of basal precipitates is markedly enhanced. Basal precipitates and β1 phases are the key strengthening precipitates in the peak-aged 1Zn alloy. Tensile tests reveal that the relatively best tensile properties are achieved in the peak-aged alloy with 0.5 wt% Zn addition, whose yield strength, ultimate tensile strength and elongation are 179 MPa, 301 MPa and 5.3%, respectively.

The microstructure, fracture mechanism and their correlation with the mechanical properties of as-cast Mg-NdZn-Zr alloy were studied, in which the effect of cooling rate on the microstructure and the mechanical properties were taken into account. The results showed that the microstructure of the alloy is composed of primary phase (alpha-Mg) and eutectic compounds. With the increase of the cooling rate in the range of 0.4-2.4 degrees C/s, the grain size of the alloy decreases from 66 mu m to 44 mu m, while the volume fraction of the eutectic compounds increases from 3% to 6.1%. The decrease of the grain size tends to improve the yield strength, ultimate tensile strength and elongation of the alloy. The eutectic compounds have complicated effects on the mechanical properties. It is found that the increase of the volume fraction of the eutectic compounds leads to the decrease of the yield strength while the network-like eutectic compounds formed at higher cooling rates decreases the ultimate tensile strength. The fracture pattern of the alloy changes from intergranular to quasi-cleavage fracture and then to a mixed fracture of intergranular and transgranular fracture with the increase of cooling rate.

The heat transfer at the casting-mould interface in resin-bonded sand mould casting of Mg-Gd-Y-Zr alloy was investigated, in which plate-shaped castings with different thicknesses were produced and the temperature variation in the casting and sand mould was recorded. The heat flux and the interfacial heat transfer coefficient (IHTC) were determined by a verified inverse heat conduction model. The results showed that the peak value of the heat flux was about 34~68 kW/m2 and it approximately increased with the decrease of the casting thickness. The averaged heat flux in the solidification process increased from 25.4 kW/m2 to 42.4 kW/m2 when the casting thickness decreased from 35 mm to 10 mm. The IHTC increases rapidly after the liquid metal was poured into the mould, and then decreases for a while, followed by a gentle increase. The averaged IHTC in the solidification process is about 105~183 W/m2K.

A phase-field model of ternary Mg-Gd-Y magnesium alloy was developed by coupling with the thermodynamics of Mg-Gd-Y system and considering cooling rate for the first time. It was applied to simulate the solidification microstructure and concentration distribution of GW103 (Mg-1.69mol%Gd-1.32mol%Y) alloy at different cooling rates both in one-grain and multigrain simulation cases. Then GW103 alloys were prepared by gravity casting method and characterized to verify the model. Results give new understanding that the GW103 alloy exhibits thick six fold primary dendrite, a few protuberance-like secondary arms and even no higher-order arms, instead of developed dendrite. The ascending cooling rate results in refinement of microstructure of GW103, which exhibits smaller grain size, slimmer primary dendrite and less secondary arms in multigrain simulation case. Besides, higher cooling rate aggravates the solute enrichment and inhomogeneous distribution of Gd and Y in interdendritic area. The simulation and the experimental results are matched well.

The effects of Ce-rich RE on the microstructure and mechanical properties of as-cast Mg-8Li-3Al-2Zn-0.5Nd-x RE（x = 0, 1, 2, 3 wt%） alloys were investigated. The results indicated that the as-cast Mg-8Li-3Al-2Zn-0.5Nd alloy mainly consisted of α-Mg, β-Li, AlLi, MgLi2 Al and Al2 Nd phases. With the addition of Ce-rich RE in the alloy,Al3 RE and Al2 RE phases generated and gradually grew into net-like or block-like structure. With the addition of RE, Al-RE phases generated by consuming Al element and, thus, less Al element was dissolved in the matrix and less AlLi phase formed. Furthermore, less AlLi phase means that more Li element released to cause the increase ofβ-Li phase and refine the α-Mg phase. Under the influence of these factors, adding more RE led to higher elongation and lower tensile strength and hardness. With the addition of Ce-rich RE, the yield strength and ultimate tensile strength of the as-cast Mg-8Li-3Al-2Zn-0.5Nd alloy gradually decreased from 180 to 152 MPa and from 215 to 193 MPa, respectively, while the elongation was remarkably improved from 21.1% to 40.2%.

The three-dimensional morphology and microstructure of the eutectics in as-cast Mg-Gd-Y-Zr alloy were investigated by using X-ray tomography technique, in which the phase constitution of the eutectics was studied by using SEM and EDS. The primary phase (α), supersaturated Mg phase (α′) and secondary phase (β) were characterized, based on which the boundaries of primary phase/eutectics and α'/β were clearly identified, and the quantification of the eutectics in the Mg-Gd-Y-Zr alloys was investigated, such as the volume fraction of the eutectics, the fraction of β phase in the eutectics (fβ/eu) and the ratio between the fraction of β and that of α’ phases (fβ/a′). Furthermore, the relationship between the microstructure and quantification of eutectics in the magnesium alloys solidified at different cooling rates were discussed. It is revealed that the eutectics of the studied alloys present complex network topology structure in the three-dimensional space, and the networks of eutectics become denser with the increase of cooling rate. Besides, the study shows that the microstructure of the eutectics, the lamellar or rod-like geometry, in the studied alloys is closely related to fβ/eu and fβ/a′ of the eutectics.

To explore the technological characteristics in fiber laser cutting of medium-thickness aluminum alloy sheets, the fiber laser cutting of an 8 mm thick AZ2219 Al alloy is carried out. The effects of process parameters such as laser power, cutting speed, defocusing distance and assistant gas pressure on the kerf quality arc systematically investigated. The kcrf quality is assessed by the dross height and the fraction of oblique striation zone of the lower part of kcrf. The experimental results show that the kcrf quality is mainly determined by laser power and assistant gas pressure. The dross height of the kcrf is reduced to minimum when laser power increases to 5.1 kW and the range of gas pressure increases to 1100-1500 kPa. Moreover, in order to further improve the kerf quality of medium-thickness aluminum alloys, a simple Laval nozzle is designed and made by the hydrodynamics simulation based on the aerodynamics theory. The experiment with this nozzle discloses shows that the fraction of oblique striation zone is reduced from 0.5 to 0.14, while the dross height does not nearly change.

对LY12铝合金蒙皮骨架结构进行碟片激光填丝焊接试验研究.结果 表明:通过激光填丝焊,铝合金可以获得焊缝表面成形良好的接头.激光功率、光丝间距、离焦量是影响焊缝成形的主要因素,激光功率3500～4000W、光丝间距0mm、离焦量+5 mm、焊接速度1.5 m/min时焊缝成形最佳.保护气流量为15L/min时,接头的抗拉强度为325MPa,达到母材强度的77％,拉伸试样断裂在热影响区靠近熔合线的位置.

The as-cast Mg-8Li-xZn-yGd (x=1, 2, 3, 4; y=1, 2; wt.%) alloys were prepared in a vacuum induction furnace and their microstructure and mechanical properties were investigated. The results show that the increase of Zn content results in the volume fraction of W-phase (Mg 3 Zn 3 Gd 2 ) increasing while that of Mg 3 Gd phase decreasing. The strength of Mg-8Li-xZn-1Gd alloys is improved with the increase of Zn content, which is ascribed to the second phase strengthening of fine strip-like W-phase and the solid solution strengthening of Zn element. For Mg-8Li-4Zn-yGd alloys, the increase of Gd content leads to the appearance of coarse and discontinuous net-like W-phase, which decreases the strength. The Mg-8Li-4Zn-1Gd alloy exhibits an optimum comprehensive performance with the yield strength, ultimate tensile strength and elongation of 154.7 MPa, 197.0 MPa and 12.4%, respectively. In addition, the aging behavior of the typical alloys was also investigated.

梳理了高强耐热镁合金的研究历程及现状.Mg-Gd(Y)-Ag和Mg-Gd(Y)-Zn系合金是目前强度最高的镁合金体系,铸造Mg-9.8Gd-2.7Y-2.0Ag-0.4Zr合金最优常温力学性能如下:抗拉强度(UTS),410 MPa;屈服强度(YS),300 MPa;延伸率(EL),2.3％.高强耐热稀土镁合金的大尺寸构件铸造工艺性亟需重点研究.总结了“固溶强化增塑”的合金设计、“高、低稀土镁合金”强韧性的设计与开发、“低稀土总量、多元合金”耦合强化设计、集成计算材料工程(ICME)等理念,对新型高强耐热铸造镁稀土合金的开发具有指导意义.

The solidification microstructure of Mg–Gd–Y–Zr alloy was investigated via an experimental study and cellular automaton (CA) simulation. In this study, step-shaped castings were produced, and the temperature variation inside the casting was recorded using thermocouples during the solidification process. The effects of the cooling rate and Zr content on the grain size of the Mg–Gd–Y–Zr alloy were studied. The results showed that the grain size decreased with an increase in the cooling rate and Zr content. Based on the experimental data, a quantitative model for calculating the heterogeneous nucleation rate was developed, and the model parameters were determined. The evolution of the solidification microstructure was simulated using the CA method, where the quantitative nucleation model was used and a solute partition coefficient was introduced to deal with the solute trapping in front of the solid–liquid (S/L) interface. The simulation results of the grain size were in good agreement with the experimental data. The simulation also showed that the fraction of the eutectics decreased with an increasing cooling rate in the range of 2.6–11.0 °C·s−1, which was verified indirectly by the experimental data.

镁合金是实际应用中最轻的金属结构材料,在航天航空、轨道交通、汽车、3C(computer,communication,consumer electronics)产品等领域具有广阔的应用前景.但镁合金材料强度偏低,尤其是高温强度,其抗蠕变性较差;镁合金铸件容易形成缩松和热裂纹,成品率低,镁合金变形件塑性加工条件控制困难,导致组织与力学性能不稳定.介绍了高性能镁合金材料(非稀土镁合金、含稀土镁合金、镁锂合金)及其成形技术(重力铸造、低压铸造、压铸、挤压铸造、半固态成形、塑性成形)的开发现状,综述了其在航天航空领域的应用状况,并展望了今后的发展趋势.

基于Mg-Gd-Y-Zr合金凝固组织与工艺条件的关系,模拟了典型航天构件组织特征参数的分布.浇铸了阶梯形铸件,并采用热电偶测量了阶梯形铸件不同厚度处在凝固过程中的温度变化.通过观察凝固组织,并与冷却条件比对,获得了凝固组织中晶粒尺寸和第二相体积分数与冷却速率的定量关系.采用ProCAST@软件模拟了典型航天构件的凝固过程,获得了凝固过程中构件不同部位的冷却速率.利用实验获得的定量关系,模拟得到了典型航天构件上晶粒尺寸和第二相体积分数的分布.

The advantages of multi-point warm press forming Corian sheet are fewly studied. In this study, the principle of multi-point warm press forming process and the geometrical relationship between multi-point punch elements and objective surface were firstly illustrated. The multi-point CAD/CAM software was used for punch height calculation and punch location adjustment. The effects of elastic cushion, forming temperature and forming force on the forming accuracy, were studied through multi-point warm press forming experiments. Then, the Corian sheets for spherical and saddle-shaped parts based on suitable forming parameters were formed through multi-point warm press forming process, and the shape errors between experimental parts and objective ones were compared. The high surface quality and shape accuracy of both spherical and saddle-shaped parts were obtained at 165 °C with the forming force of 100 kN. It confirms that the multi-point warm press forming process is feasible for manufacturing Corian sheets.