Research progress on semi-continuous casting of magnesium alloys under external field

High-performance magnesium alloys are moving towards a trend of being produced on a large scale and in an integrated manner.The foundational key to their successful production is the high-quality cast ingots.Magnesium alloys produced through the conventional semi-continuous casting process inevitably contain casting defects,which makes it challenging to manufacture high-quality ingots.The integration of external field assisted controlled solidification technology,which combines physical fields such as electromagnetic and ultrasonic fields with traditional semi-continuous casting processes,enables the production of high-quality magnesium alloy ingots characterized by a homogeneous microstructure and absence of cracks.This article mainly summarizes the technical principles of those external field assisted casting process.The focus is on elaborating the refinement mechanism of different types of electromagnetic fields,ultrasonic fields,and combined physical fields during the solidification of magnesium alloys.Finally,the development prospects of producing highquality magnesium alloy ingots through semi-continuous casting under the external field were discussed.

Direct-chill semi-continuous casting process of three-layer composite ingot of 4045/3004/4045 aluminum alloys

Three-layer composite ingot of 4045/3004/4045 aluminum alloys was prepared by direct-chill semi-continuous casting process,the temperature field distribution near the composite interface,macro-morphology,microstructure and composition distribution of the composite interface were investigated.The results show that semi-solid layer with a certain thickness forms near the interface due to the effect of cooling plate,which ensures successful implementation of casting the composite ingot.Two different aluminum alloys are well bonded metallurgically.The mechanical properties of composite interface were measured,the tensile and shearing strengths of composite interface are 105 and 88 MPa,respectively,which proves that the composite interface is a kind of metallurgical bonding.

Effects of casting process on microstructures and flow stress behavior of Mg-9Gd-3Y-1.5Zn-0.8Zr semi-continuous casting billets

Mg-9Gd-3Y-1.5Zn-0.8Zr alloys own high strength,good heat and corrosion resistance.However,it is difficult for the fabrication of large-scale billets,due to the poor deformation ability and strong hot-crack tendency.This work investigated the casting process on the microstructures and flow stress behaviors of the semi-continuous casting billets for the fabrication of large-scale Mg-9Gd-3Y-1.5Zn-0.8Zr billets.The casting process(electromagnetic intensity and casting speed)shows outstanding effects on the microstructures and flow stress behavior of the billets.The billets with the specific casting process(I=68 A,V=65 mm/min)exhibit uniform microstructures and good deformation uniformity.

Effect of high-intensity ultrasonic field on process of semi-continuous casting for AZ80 magnesium alloy billets

Under the high-intensity ultrasonic field,AZ80 magnesium alloy was semi-continuously cast.The effects of ultrasonic intensity on the as-cast microstructures and mechanical properties were investigated.The results show that the microstructures of the alloy cast under high-intensity ultrasonic field are fine and uniform,and the grains are equiaxed,rose-shaped or globular with an average size of 257μm.High-intensity field significantly decreases the grain size,changes the morphologies of theβ-Mg17Al12 phases and reduces their area fraction.It is also shown that a proper increase in ultrasonic intensity is helpful to obtain fine,uniform and equiaxed as-cast microstructures.The optimum ultrasonic parameters are that frequency is 20 kHz and ultrasonic intensity is 1 368 W.The mechanical tests show that the mechanical properties of the as-cast AZ80 magnesium alloy billets cast under ultrasonic field are greatly improved,and with increasing the ultrasonic intensity,the mechanical properties of the entire alloy billets are much higher and more uniform than those of the alloy without ultrasonic field.

Effects of heat treatment on microstructure and mechanical properties of Mg-8Gd-3Y-0.5Zr(wt.%)alloy fabricated by semi-continuous casting

The microstucture, mechanical properties and fracture behaviors of semi-continuous cast Mg-8Gd- 3Y-0.5Zr （wt.%, GW83K） alloy after different heat treatments were investigated. Almost all the eutectic compounds were dissolved into the matrix and there was no evident grain growth after optimum solution treatment at 500 ~C for 4 h. Further ageing at low temperatures led to significant precipitation hardening, which strengthened the alloy. Peak-aged at 200℃, the alloy had the highest ultimate tensile strength （UTS） and lowest elongation at 395 MPa and 2.8%, respectively. When aged at 225℃ for 15 h, the alloy exhibited prominent mechanical performance with UTS and elongation of 363 MPa and 5.8 %, respectively. With regard to microstructure and tensile properties, the processes of 500℃, 4 h ＋ 225℃, 15 h are selected as the optimal heat treatment conditions. The alloy under different conditions shows different fracture behaviors： in the as-cast alloy, a quasi-cleavage pattern is observed; after solution treatment, the alloy exhibits a trans-granular quasi-cleavage fracture; after being peak-aged at 200℃ and 225℃, the fracture mode is a mixed mode of trans-granular and inter-granular fracture, in which the inter-granular mode is dominant in the alloy peak-aged at 200℃.

Microstructure and mechanical properties of AZ31 alloy ingot fabricated by semi-continuous casting

The AZ31 alloy ingot with diameter of 110 mm and length of 3500 mm was fabricated successfully. The compositions and microstructure morphologies of the ingot at different locations were performed, which indicated that the chemical composition distributed homogeneously through the whole alloy ingot and the average grain size increased from the surface to the center. The results of the EDS and element face-scanning illustrated that the eutectic compounds mainly consisted of fl-Mg17Al12 and a small amount of fl-Mgl7（AlZn）12. Furthermore, slight improvements of the strength and ductility were observed from the center to the surface along the axial direction of the alloy ingot, while both the strength and elongation to failure of the samples along the radial direction are higher than that along the axial direction. The fine grain strengthening was the main contributors to the strength of the as-casted AZ31 alloy.

Effect of Middle-frequency Electromagnetic Field on the Semi-continuous Casting for ZK60 Billets

The semi-continuous casting of ZK60 magnesium alloy under different middle frequency electromagnetic field conditions was examined.Effects of middle frequency electromagnetic field on microstructure,precipitations and tensile properties are investigated.The results show that the microstructures of ZK60 magnesium alloy are refined and distribution uniformity of precipitations is observed after applying the middle frequency electromagnetic field.And the tensile properties of the billets produced by middle frequency electromagnetic field are increased.

Effect of Cooling Intensity and Position on Solidification in Semi-Continuous Casting of Copper

Cooling heat flux effect in both primary and secondary cooling zone has been studied in semi-continuous casting of copper billet. Sufficient cooling is essential to reduce casting defects and to get high productivity, however low rate of solidification is aimed in order to get coarser grain size and softer metal for less losses in extrusion. A three-dimensional numerical model has been developed including solidification behavior of copper through mushy zone. At steady state and constant casting speed, solid shell thickness is monitored during the reduction of cooling rate at mould region to avoid breaking out. Heat flux intensity at mould plays important role not only in the formation of solid shell thickness. But, pool length and mushy zone thickness can be significantly increased by decreasing primary cooling intensity. Increase intensity of secondary cooling zone for two particular cases of primary cooling is tested. First case is tested at mould inlet water temperature of 38°C, and second case at water temperature of 63°C. Results showed that the combination of increasing secondary cooling intensity and reduction of primary cooling intensity can increase pool length and mushy zone thickness. Also, it is shown that, secondary cooling intensity can be magnified by up to 1.5 times for cooling water temperature of 63°C to get pool length close to that of water temperature of 38°C.

Effects of Ce on microstructure of semi-continuously cast Mg-1.5Zn-0.2Zr magnesium alloy ingots

Mg-1.5Zn-0.2Zr-xCe (x=0, 0.1, 0.3, 0.5, mass fraction, %) alloys were prepared by conventional semi-continuous casting. The effect of rare earth Ce on the microstructure of Mg-1.5Zn-0.2Zr-xCe alloys was studied and the distribution of Ce was analyzed by optical microscopy (OM), X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results indicate that Ce element exists in the form of Mg12Ce phase and has an obvious refining effect on the microstructure of test alloys. As the Ce content increases, the grain size reduces, the grain boundaries turn thinner, and the distribution of Mg12Ce precipitates becomes more and more dispersed. The Mg-1.5Zn-0.2Zr alloy with 0.3%Ce has the best refinement effect. From center to periphery of the ingot, the amount of granular precipitates in the grain reduces. In longitudinal section of the ingot, some relative long columnar grains appear.

Inhomogeneity of microstructure and mechanical properties of a 500 mm diameter heavy section semi-continuous cast AZ61 magnesium alloy ingot

For the large magnesium alloy ingot, there is a considerable difference in cooling rate of different parts in the ingot, which leads to non-uniform distribution of the secondary phases, solute segregation and tensile properties. In the present research, an heavy AZ61 alloy ingot with a diameter of 500 mm was made by semi-continuous casting. The microstructure and mechanical properties at different positions along the radial direction of the large ingot were investigated by using an optical microscope(OM), a scanning electron microscope(SEM), an energy dispersive spectroscope(EDS), and a micro-hardness tester. The results indicate that the microstructure of the AZ61 ingot is non-uniform in different locations. It changes from equiaxed to columnar grains from the center to the edge; the average grain size gradually reduces from 1,005 μm to 763 μm, the secondary dendrite arm spacing reduces from 78 μm to 50 μm, and the Mg17(Al,Zn)12 phase is also refined. The micro-hardness value increases from 55.4 HV at the center to 72.5 HV at the edge of the ingot due to the microstructure differences, and the distribution of micro-hardness at the edge of the ingot is more uniform than that in the center. The tensile properties at room temperature show little difference from the center to the edge of the ingot except that the elongation at the edge is only 3.5%, much lower than that at other areas. The fracture mechanism is ductile fracture at the center and cleavage fracture at the edge of the ingot, and at the 1/2 radius of the ingot, a mixture of ductile and cleavage fracture is present.

Effect of ultrasonic power and casting speed on solidification structure of 7050 aluminum alloy ingot in ultrasonic field

With the experiment and finite element simulation, the influences of power ultrasonic on the solidification structure of 7050 aluminum alloy ingot in semi-continuous casting were researched, and the effects of casting speed on solidification structure in ultrasonic field were also analyzed. The experiment and simulation results show that the solidification structure of the ingot is homogeneously distributed, and its grain size is obviously refined at ultrasonic power of 240 W. The average grain sizes, which can be seen from the Leica microscope, are less than 100 μm. When the casting speed is 45-50 mm/min, the best grain refinement is obtained.

As-cast structure of DC casting 7075 aluminum alloy obtained under dual-frequency electromagnetic field

We have experimentally determined the as-cast structures of semi-continuous casting 7075 aluminum alloy obtained in the pres-ence of dual-frequency electromagnetic field. Results suggest that the use of dual-frequency electromagnetic field during the semi-continuous casting process of 7075 aluminum alloy ingots reduces the thickness of the surface segregation layer, increases the height of the melt menis-cus, enhances the surface quality of the ingot, and changes the surface morphology of the melt pool. Moreover, low-frequency electromag-netic field was found to show the most obvious influence on improving the as-cast structure because of its high permeability in conductors.

Microstructure and mechanical properties of large-scale Mg-Gd-Y-Zn-Mn alloys prepared through semi-continuous casting

Large-scale Mg-8Gd-4Y-1Zn-Mn(wt.%)alloy ingot with a diameter of 315 mm and a length of 2410 mm was prepared through semi-continuous casting.Chemical composition,microstructure and mechanical properties at different locations of the samples with as-cast,T4 and T6 heat-treated states,respectively,were investigated.No obvious macro segregation has been detected in the high-quality alloy ingot.The main eutectic structures at all different locations are composed ofα-Mg,Mg3RE-type,Mg5RE-type and LPSO phases.At the edge of ingot,the unusual casting twins including 10-12 extension twins and 10-11 compression twins were observed due to the intensive internal stress.In T4 heat-treated alloy,the micro segregation was eliminated.The remained phases wereα-Mg and LPSO phase.Combined with the remarkable age-hardening response,T6 samples exhibits improved mechanical properties at ambient temperature,which derives from the dense prismaticβ'precipitates and profuse basalγ'precipitates.

CAST-深床反硝化滤池工艺处理城市污水效果研究

水解酸化-CAST工艺在城市污水处理中广泛使用,但存在着脱氮除磷效果差,出水总磷偏高的问题。本文通过工程实例,采用水解酸化-CAST-深床反硝化滤池工艺,在不增加运行成本前提下,弥补了水解酸化-CAST工艺的不足,改善了出水水质。该工艺正常运行后,出水达到现行GB18918-2002(一级A)标准,而且更节能、更安全。通过实施新的工艺流程,达到节能、减排、减污、增效的目的。

Deep lingual arterial chemoembolization of tongue carcinoma with microcapsuled anticancer drug

Objective: Microcapsule chemoembolism is a promising treatment of tumors. We describe a deep lingual arterial embolization of tongue carcinoma with microcapsuled carboplatinum. Methods: Lingual artery cast specimens from cadavers were microscopically examined, and 78 patients with tongue cancer were recruited and treated with the deep lingual arterial embolization therapy. Results: Microcapsule embolism occurred approximately at the fifth or sixth level of the deep lingual artery branches. The five-year survival rate was 88.5% (69 out of 78), and the ten-year survival rate 52.6% (41 out of 78). Conclusion: The deep lingual arterial embolization of tongue carcinoma with microcapsuled carboplatinum is an effective therapy to treat carcinoma in mid-margin or mid-body of the tongue.

A new composite material produced by semi-continuous casting

A new composite material consisting of lxxx aluminum alloy and 7xxx aluminum alloy was produced by semi-continuous casting. Macrostructure, microstructure, composition distribution and hardness distribution of composite interface were analyzed. Macrostructure shows that composite interface is planar and clean with little evidence of porosity; microstructure shows that composite interface is a kind of metallurgical bonding; composition and hardness distributions have a good corresponding relationship. At the same time, the mechanical property of composite interface was measured, the tensile strength is 71 MPa, the shearing strength is 62 MPa and the bending strength is 142.5 MPa, which can also show that composite interface is a kind of metallurgical bonding. Temperature distribution of composite interface was obtained by measuring temperatures near composite interface in lxxx aluminum alloy.

铸瓷粘结桥修复深覆[牙合]伴单颗前牙缺失的临床效果

目的探讨铸瓷粘接桥修复深覆[牙合]伴单颗前牙缺失患者的临床疗效。方法选取2023年1月—2023年6月安徽医专附属口腔医院就诊的30例深覆[牙合]伴前牙单颗缺失的患者作为研究对象,唇侧制作铸瓷粘接桥,术后1周和6个月分别检查修复体脱落、修复体折裂、边缘密合性、继发龋、边缘着色、牙周健康状况等。结果术后1周修复效果较好,无修复体脱落及折断,边缘密合性好、无着色,牙周健康。术后6个月检查见2例修复体脱落,重新粘结后继续使用,1例探针可探及边缘,牙龈轻度炎症,其余27例未见异常,未见修复体脱落和折断,边缘密合性好,基牙无龋坏,牙周健康。结论铸瓷粘接桥修深覆[牙合]伴单颗前牙缺失患者短期临床效果较好。

基于双向加权特征融合网络的铸件内部缺陷检测方法

针对X射线无损探伤过程中铸件内部缺陷小、对比度弱、人工识别效率低等问题,提出了一种基于双向加权特征融合网络的铸件内部缺陷检测方法。在YOLOv5网络模型基础上引入改进的坐标注意力模块(NCA),以提高网络对不规则缺陷和小缺陷的学习能力;引入双向特征金字塔网络(BiFPN)代替原有路径聚合网络(PANet),以实现缺陷特征多尺度高效融合,并使用EIoU Loss回归损失函数提高缺陷边界框定位的精度。试验结果表明,本文所提方法对铸件内部小目标、弱对比度缺陷具有良好的检测性能。

基于改进DCGAN的铸件表面缺陷生成方法

为解决传统数据增强仅通过改变和翻转图像无法生成新的铸件表面缺陷图像且泛化能力较差等问题,通过修改网络结构并将注意力机制嵌入深度卷积生成对抗网络DCGAN模型中,实现更丰富的特征聚合,加强关键信息的交互,同时用MetaAconc激活函数替代ReLU激活函数,提升网络的自适应激活能力,增强模型训练的稳定性,并提出AMDCGAN模型。实验结果表明,相比DCGAN模型,AMDCGAN模型生成图像的FID值从19.07降至8.06,能更有效地完成铸件表面缺陷图像的生成任务。

优化医学影像三维渲染可视化效果:技术综述

医学成像学是医学领域的一个重要分支,目前最常见的医学成像方式主要包括:磁共振成像、计算机断层扫描、超声成像、X射线、正电子发射断层扫描等。医学影像是通过各种成像技术获取信息实体,医学影像三维渲染是医学成像领域使用的一种可视化技术,对于可视化解剖结构、精准诊疗、手术规划等具有重要意义。分析医学影像三维渲染技术在可视化效果优化的研究现状,首先介绍了2种基础的三维渲染技术,然后从优化技术和框架两方面入手,介绍当前三维渲染可视化的优化研究,比较不同技术的特点、使用环境以及优缺点,为相关研究人员选择不同的技术提供参考,最后从主观和客观两方面介绍如何评价三维渲染的可视化效果。讨论了在技术发展过程中,存在引入的算法复杂度高、渲染效率降低、算法实时性差的问题,并思考解决这些问题的方法,探讨优化三维渲染可视化效果的未来发展方向。