Thermodynamic analysis on tin precipitation behavior in Ti-bearing peritectic steel after magnesium treatment

TiN,which is ubiquitous in Ti-bearing steel,has a critical influence on both the mechanical properties and the welding process of steel,and therefore researche on the precipitation behavior of TiN in molten steel bath is of great significance.In this paper,Ti-bearing peritectic steel was taken as the study object and FactSage was adopted to explore how the precipitation behavior of typical inclusions in steel was affected by the steel composition.Furthermore,microsegregation models were used to analyze the precipitation process of TiN at solidification front,and the calculation results were finally verified by scanning electron microscope(SEM).Research showed that a multitude of dispersed particles of high melting oxide MgAl2O4 or MgO always existed in molten steel after magnesium treatment.In consideration of the segregation and enrichment of solute elements at the solidification front,the Ohnaka microsegregation model was employed to compute the precipitation during solidification.In the event of the solid fraction reaching 0.95 or more,the concentration product of[Ti][N]at the solidification front exceeded the equilibrium concentration product,then TiN began to precipitate.MgO or MgAl2O4 cores were generally found in TiN particles of peritectic steel after the magnesium treatment,which was consistent with the thermodynamic calculation results.Moreover,the average size of TiN particles was reduced by approximately 49%.This demonstrated that Mg-rich high melting inclusions were formed after the magnesium treatment,by which the heterogeneous nucleation of TiN was promoted it;therefore,favorable nucleation sites were provided for further refining the high-temperature ferrite phase.

Formation and evolution behavior of inclusions in Al-killed resulfurized free-cutting steel with magnesium treatment

To reveal the formation and evolution behavior of inclusions during magnesium treatment and resulfurization in Al-killed free-cutting steel, both laboratory experiments and thermodynamic calculations were carried out. The extracted samples were polished and analyzed by scanning electron microscopy and energy-dispersive spectroscopy. The results indicated that MgO formed immediately and then transferred to MgO·Al2O3 with the homogenization of [Mg] in steel in the case of low magnesium addition (w[Mg] < 0.0020%). However, MgO would keep stable in the case of high magnesium addition (w[Mg] ≥ 0.0020%). In the process of resulfurization, the addition of sulfur forced the transformation of MgO to MgO·Al2O3 accompanied with the formation of MgS if the mass fraction of [S] in steel was in the range 0.15%-0.70%. MgS precipi-tated as a solid solution containing a quantity of MnS, and the composition of the sulfide solution was calculated to be (Mg0.85Mn0.15)S when the mass fraction of [Mn] was 1.2%. The formation mechanisms of inclusions after magnesium and sulfur additions were discussed comprehensively, and proper models for the evolution of inclusions were set up.

Research Progress on the Application of Magnesium Hydroxide in the Industrial Wastewater Treatment Filed

The research progress on the application of magnesium compounds (magnesium hydroxide,light calcined magnesia,magnesium chloride,sea water,brine,dry brine,etc.) which were represented by magnesium hydroxide in the wastewater treatment filed was comprehensively commentated.Meanwhile,the prospects of application were discussed.Considering the magnesium resources in China were characterized with rich classes,abundant reserves,vast distribution and high quality,it's important to make great efforts to research and exploit magnesium products,especially the exploitation of their meticulous use way.It had the practical significance for the sustainable development of economy in China.

Microstructure and mechanical properties of AZ91 magnesium alloy subject to deep cryogenic treatments

AZ91 magnesium alloy was subjected to a deep cryogenic treatment. X-ray diffraction （XRD）, scanning electronic microscopy （SEM）, and transmission electronic microscopy （TEM） methods were utilized to characterize the composition and microstructure of the treated samples. The results show that after two cryogenic treatments, the quantity of the precipitate hardening β phase increases, and the sizes of the precipitates are refined from 8-10μm to 2-4μm. This is expected to be due to the decreased solubility of aluminum in the matrix at low temperature and the significant plastic deformation owing to internal differences in thermal contraction between phases and grains. The polycrystalline matrix is also noticeably refined, with the sizes of the subsequent nanocrystalline grains in the range of 50-100 nm. High density dislocations are observed to pile up at the grain boundaries, inducing the dynamic recrystallization of the microstructure, leading to the generation of a nanocrystalline grain structure. After two deep cryogenic treatments, the tensile strength and elongation are found to be substantially increased, rising from 243 MPa and 4.4% of as-cast state to 299 MPa and 5.1%.

EFFECTS OF TREATMENT TIME ON CORROSION OF DIFFUSION-ALLOYED COATINGS OF PURE MAGNESIUM

The corrosion resistance of pure magnesium with surface alloying layer obtained by a solid diffusion alloying technique has been analyzed. To establish the optimum treatment time, the experiments were performed at 480℃ for different solid diffusion time （8, 16, and 24h）. The diffusion interaction effectiveness between Zn, Al mix powder and the sample surface, depending on the treatment time for diffusion at given temperatures, has an obvious influence on corrosion resistance and corrosion mechanism. Corrosion properties were studied using the constant immersion test （in 3.0% NaCl solution, temperature is （28±1）℃, and time is 96h）. Optical microscopy （OM） and EDS （energy dispersive spectrum） composition analysis were used to examine the cross-sectional microstructural characteristics of alloyed layer of treated samples. It is shown that in comparison with the untreated samples, the treated ones possess a better corrosion resistance. The Al5Mg11Zn4 phase, which formed as a continuous phase due to the diffusion of Al, Zn, and Mg elements and subsequent interaction on the outermost layer of diffusion alloying zones （especially the samples treated for 24h at 480℃）, was inert to the chloride solution compared with pure magnesium and acted as a corrosion barrier, and therefore the best corrosion resistance was obtained. This protective action of Al5Mg11Zn4 phase was found to change with its amount, which was controlled by the diffusion time at given temperature. It was concluded that the continuous Al5Mg11Zn4 phase （WP-zone） of the reacted layer in pure magnesium was beneficial from the point of view of corrosion resistance.

Effect of thermomechanical treatment on microstructure and hardness behavior of AZ63 magnesium alloy

Due to their high specific strength and low density, magnesium alloys are widely used in many weight-saving applications. This research is aimed at investigating the microstructure and hardness of commercial AZ63 alloy specimens subjected to two different thermomechanical treatments （TMTs）. For the first TMT, after solution treated at the temperature of 380 ℃ for 20 h, AZ63 alloy specimens were 5% cold worked by rolling process followed by ageing at the temperatures of 150 ℃and 250 ℃ for 3, 9 and 25 h. In the second TMT, the specimens were solution treated at the temperature of 380 ℃ for 20 h, underwent 2% cold worked and quenched in water of 0 ℃. Half of the specimens were then 2% cold worked whilst the rest were rolled to 8% cold worked. All the specimens were then aged at the temperatures of 150 ℃ and 250 ℃ for 3, 9 and 25 h. Optical microscope was used to analyze the microstructures of the specimens. Hardness test was too conducted to measure the effect of the treatments on the specimens. Results show that two-step aging enhances the hardness of the specimens due to the distribution of fine β-phase （MglTA112） in the alloy matrix. The results also reveal that, the best hardness from the first TMT was produced by specimen that was pre-aged at 150 ℃ whereas, in the second TMT, aging at 250 ℃ exhibited the best hardness values.

Effects of heat treatment on the microstructure and mechanical properties of ZA84 magnesium alloy

The effects of heat treatment on the microstructure and mechanical properties of ZA84 （Mg-8Zn-4Al-0.25Mn） alloy were investigated. The results indicate that the as-cast microstructure of the alloy is mainly composed of α-Mg matrix and two different morphologies of precipitates （continuous and quasi-continuous Mg32（Al,Zn）49 phases and isolated Mg5Al2Zn2 phases）. After solid solution treatment at 345℃, the Mg32（Al,Zn）49 phases change from continuous and quasi-continuous net to disconnected acute angle shape, and parts of second phases sphericize. The optimum heat treatment condition for the alloy is solution treatment at 345℃ for 48 h and water quenching, then aging treatment at 200℃ for 12 h and atmosphere cooling. Under the optimum condition, the ulti- mate tensile strength and yield strength of the alloy can be imoroved, but the elongation is not effected much bv heat treatment.

Effects of solution and aging treatments on microstructures and mechanical properties of AZ61 magnesium alloy welded joints

The effects of solution and aging treatments on the microstructures and mechanical properties of tungsten inert gas arc welded AZ61 magne-sium alloy joints were investigated by microstructural observations,microhardness tests and tensile tests.The results showed that the solution treatment led to the β-Mg17Al12 particles dissolved into the α-Mg grains.Hence,the microhardness of the fusion zone and the ultimate tensile strength of the welded joints were the lowest.With the increase of the aging temperature,the volume fraction of the β-Mg17Al12 particles in the fusion zone increased and this enhanced the microhardness of the fusion zone gradually.Also,the elongation of the welded joints was in-creased slightly with the increase of the volume fraction of the β-Mg17Al12 particles.However,the ultimate tensile strength of the welded joints increased at first and dropped at 190 ?C due to cracks formed at the boundaries of the β-Mg17Al12 particles.

Effect of Post-weld Heat Treatment on Mechanical Characteristics of AZ31 Magnesium Alloy Welded Joints

Tungsten inert gas（TIG） welding was performed on 2.7 mm thick commercial extruded AZ31 B magnesium alloy plates. We investigated the effect of post-weld heat treatment（PWHT） on the microstructure, mechanical properties and precipitated phase of the weld joints. The results showed that during the annealing treatment（200 ℃-1 h, 250 ℃-1 h, 300 ℃-1 h, 350 ℃-1 h, 400 ℃-1 h, and 450 ℃-1 h）, the average grain size in the weld seam was the minimum after annealing at 400 ℃ for 1 hour, and then abnormally grew up after annealing at 450 ℃ for 1 hour. The mechanical properties enhanced when the joints were processed from 200 ℃-1 h to 400 ℃-1 h but sharply decreased with increasing annealing temperature. In contrast to the annealing treatment, solution treatment（250 ℃-10 h, 300 ℃-10 h, 350 ℃-10 h, 400 ℃-10 h, and 450 ℃-10 h） exhibited a better ductility but a slight deterioration in tensile strength. Especially speaking, no eutectic compounds（such as Mg17 Al12） were observed in the weld seam. The supersaturated Al atoms were precipitated in a coarse spherical shape dispersed in the weld seam. The precipitated Al atoms dissolved in the matrix substances at the condition（400 ℃-1 h） or（250 ℃-10 h）. The solution treatment caused grain coarsening and precipitated Al atoms dissolved in the weld seam substantially, which resulted in a drop in micro-hardness at the weld seam compared to the area of the annealed joints.

Improvement of Bonding Strength of AZ31B Magnesium Alloy by Anodizing and Chromium-free Conversion Treatments

The influences of chromium-free chemical conversion treatment and anodizing treatment on bonding strength of AZ31 magnesium alloy were studied by lap-shear test, SEM and electrochemical methods. Both chemical conversion treatment and anodizing can increase the bonding strength. The anodizing treatment gives higher bonding strength and better corrosion resistance than chemical conversion treatment. The increase of bonding strength by the treatmetlts may be attributed to the uneven surface structures with micro-pores, resulting in increased bonding areas and the embedding effect.

Improving the fatigue property of welded joints for AZ31 magnesium alloy by ultrasonic peening treatment

The fatigue property of AZ31 magnesium alloy and its TIG welded joints were investigated. The ultrasonic peening treatment （UPT） was used to improve the fatigue property of the TIG welded joints, which was treated at the weld toe by the UPT process. The test results show that the fatigue strength of the base metal of AZ31 magnesium alloys is 57.8 MPa, and those of the fillet joint and the transverse cross joint are respectively 20. 0 MPa and 17.2 MPa at 2 × 10^6 cycles. The fatigue strengths of two kinds of welded joints treated by the UPT are respectively 30. 3 MPa and 24. 7 MPa, which have been improved by 51.5% and 43.6%, respectively. The fatigue life of the fillet joint specimens is prolonged by about 2. 74 times and the fatigue life of the transverse cross joint specimens is prolonged by about 1.05 times when the stress range is at 40. 0 MPa.

Improved Corrosion Resistance of Magnesium Alloys AZ31 and AZ91HP by High Current Pulsed Electron Beam Treatment

Surface treatment of magnesium alloys AZ31 and AZ91HP by a high current pulsed electron beam (HCPEB) was investigated in the present paper. The corrosion resistance of treated samples was tested in a 5% (wt%) NaCl solution, showing remarkably improvement as manifested by polarization curves. According to EPMA analysis, the intermetallic Mg17Al12 in the surface layer of AZ91HP sample almost disappeared after the treatment of HCPEB, leaving the surface layer in a state of supersaturated solid solution. Both the augmentation of aluminum content and the formation of supersaturated structure in the surface layer are believed to contribute to the improved corrosion resistance of AZ31 and AZ91HP.

Effects of trace Cr on as-cast microstructure and microstructural evolution of semi-solid isothermal heat treatment ZC61 magnesium alloy

The content and kind of trace elements in magnesium alloys have important effects on their ascast and semi-solid microstructures. In this research work, effects of trace Cr on as-cast and semi-solid microstructures of ZC61 magnesium alloy were investigated by metal mold casting and semi-solid isothermal heat treatment. The results show that the addition of Cr can refine the α-Mg phase without generating a new phase, noticeably change the eutectic phase, and decrease the average size of solid particles at the same isothermal heat treatment conditions. Non-dendritic microstructures of all alloys are constituted of α_1-Mg phases, α_2-Mg phases and eutectic phases after water quenching. With isothermal temperature increased or holding time prolonged, the eutectic microstructure(α-Mg+MgZn_2+CuMgZn) at the grain boundaries in as-cast alloy is melted preferentially and then turned into semi-solid non-dendritic microstructure by processes of initial coarsening, microstructure separation, spheroidizing and final coarsening. Especially when the ZC61-0.1 Cr alloy was treated at 585 ℃ for 30 min, the ideal non-dendritic microstructure can be obtained, and the corresponding solid particle size and shape factor were 37.5 μm and 1.33, respectively. The coarsening process of solid α-Mg phase at higher temperature or longer time, which is affected by both combining growth and Ostwald ripening mechanism, is refrained when Cr is added to the ZC61 alloy.

盾构淤泥质废弃黏土氧化镁固化-碳化试验及碳化机制研究

盾构隧道施工产生的废弃土面临堆放、运输及处理等难题,将原材料丰富、生产耗能少、环境友好的MgO用于废弃土固化处理是一个值得探索的方法。通过改变MgO掺量a_(m)、养护龄期T、碳化时间H研究MgO固化-碳化淤泥质废弃黏土界限含水率w、无侧限抗压强度q_(u)、弹性模量E_(50),结合微观形貌及矿物成分变化规律探讨其固化-碳化机制。结果表明:MgO固化-碳化具有明显的加固土体效果,加固效果随a_(m)、T呈先上升后趋于稳定的趋势,随H呈先上升后下降的趋势;不同a_(m)、T下,碳化4h会使土体塑性指数I_(P)降低57%以上,土体可塑性显著下降;不同a_(m)和T的固化-碳化土q_(u)均在H为4h时取得峰值,最高可达1.4MPa,比碳化前强度提升了220%~350%;固化-碳化反应对土体的E_(50)提升受a_(m)影响较大,当a_(m)超过9%时,碳化4h试样的E_(50)增幅在500%左右;MgO固化-碳化过程中水化产物、碳化产物不断生成和发育,形成网状、花朵聚集状的形貌,填充土颗粒间的孔隙,增强了土颗粒间的胶结作用,土体结构更为密实。该研究为长三角地区土压盾构产生的淤泥质废弃黏土的固化-碳化处理与再利用提供了思路。

镁合金表面涂层技术研究与展望

镁合金因其质量轻、比强度高、电磁屏蔽性能良好等优点被广泛应用到各种行业,但是由于镁合金极易发生腐蚀,导致镁合金抗腐蚀性能差,严重缩短了镁合金部件的使用寿命,造成镁合金应用范围变的局限。为了解决镁合金使用范围不广泛和抗腐蚀性差等问题,大批科学家进行了大量的研究。本文从镁合金表面处理技术研究进展出发,概述了近年来镁合金表面涂层制备的主要方法,并对镁合金涂层的研究方向与应用前景进行了展望。

硫酸镁辅助镇痛效果及在无阿片类药物麻醉方案中的应用前景

在疼痛治疗过程中为了减少阿片药物的应用,已经尝试引入辅助镇痛剂。越来越多的数据表明N-甲基-D-天冬氨酸(NMDA)受体拮抗剂可能具有增强阿片样物质的镇痛作用,诸多研究显示硫酸镁的辅助镇痛作用在疼痛治疗和围手术期麻醉方面表现出很好的应用前景。硫酸镁应用于疼痛治疗的药理学机制主要是其具有NMDA偶联通道的生理电压依赖性阻断剂的作用,其抗伤害性作用与镁阻断钙内流,从而抑制中枢敏感化并降低先前存在的痛觉过敏有关。该文综述硫酸镁在围手术期应用的现状,主要介绍硫酸镁静脉给药、鞘内给药、局部给药的辅助镇痛效果和减少阿片类药物消耗作用,以及在无阿片类药物麻醉方案中的作用及应用前景。

Ce变质铸造汽车用AZ61镁合金的组织与力学性能

对AZ61镁合金进行了不同Ce添加量的变质铸造试验,通过OM、硬度测试、拉伸试验等手段研究了Ce变质处理对AZ61镁合金组织与力学性能的影响。结果表明:未变质的AZ61镁合金铸态组织由α-Mg相和粗大网状β-Mg17Al12相组成。随着Ce加入量的增加,AZ61镁合金中β-Mg17Al12相析出量逐渐减少,稀土相逐渐增多,β-Mg17Al12相由连续粗大网状逐渐转变为颗粒状,Ce添加量1.0wt%的AZ61镁合金中β-Mg17Al12相最为细小。与未变质的AZ61镁合金相比,经Ce变质的AZ61镁合金的硬度、抗拉强度和伸长率均有了明显提高。随着Ce加入量的增加,AZ61镁合金的硬度、抗拉强度和伸长率均先升高后降低,Ce添加量1.0wt%的AZ61镁合金的力学性能最佳。

AZ31B镁合金钒/硅烷复合转化膜的制备与表征

目的改善钒酸盐转化膜表面形貌,提高单一钒酸盐转化膜的耐蚀性能。方法使用偏钒酸盐和硅烷通过两步法在镁合金表面制备钒/硅烷复合转化膜,比较不同硅烷制备的复合膜的耐蚀性能,从而确定使用硅烷的种类,采用扫描电子显微镜(SEM)、X射线能谱(EDS)、X射线光电子能谱(XPS)和傅里叶红外光谱(FT-IR)观察转化膜的微观形貌并分析转化膜的组成和结构,通过交流阻抗测试(EIS)、Tafel极化曲线测试和全浸腐蚀实验评价转化膜的耐蚀性能,并采用划格实验和接触角测试评价转化膜的结合力和疏水性。结果确定使用BTEPST(双-[3-(三乙氧基硅)丙基]-四硫化物)作为成膜组分,使用偏钒酸钠和BTESPT在镁合金表面成功制备钒/BTESPT复合膜,复合膜表面均匀平整,致密无裂纹,与基体结合力好,具有疏水性,该复合膜的组成元素为Mg、V、C、O、Si和S,且元素分布较均匀,膜层是包含Si—O—S、Si—O—Mg、Si—O—V等共价键的交联结构。交流阻抗测试结果显示,钒/BTESPT复合转化膜的膜层电阻为1.17×10^(5)Ω·cm^(2),电荷转移电阻为1.076×10^(5)Ω·cm^(2)。极化曲线测试结果表明,复合膜的腐蚀电位为-1.4570V,腐蚀电流密度为1.4980×10^(-7)A·cm^(-2),腐蚀电流密度相较于基体降低约2个数量级,对镁合金的保护效率达到99.6%。复合转化膜在3.5%(质量分数)NaCl溶液中长期浸泡10d未发生明显腐蚀,全浸实验浸泡14d腐蚀速率为0.0580 g/(m^(2)·h),未处理的镁合金腐蚀速率则为0.5186 g/(m^(2)·h)。结论钒/BTESPT复合膜能进一步提高钒酸盐转化膜对AZ31B镁合金的保护性能。

镁处理对TiN液析行为的影响

为研究镁处理对钛微合金钢在凝固过程中TiN液析行为的影响,采用真空感应炉冶炼了试验钢.利用SEM-EDS结合图像处理软件,分析铸坯径向不同位置处镁处理钢对比非镁处理钢中夹杂物的成分和尺寸变化,并用FactSage软件对夹杂物的形成和析出进行了计算.结果表明:钢中TiN夹杂均在凝固前沿的液相中生成.氮含量增加,凝固过程中TiN的析出温度升高和析出量增加,并对后续Ti4C2S2和MnS的析出产生影响.非镁处理条件下,铸坯1/4处和中心处TiN夹杂的平均粒径分别为2.48和2.11μm,镁处理后,尺寸分别降为1.50,1.45μm和1.48,1.38μm,数密度也有所增大.添加微量Mg,MgO·Al_(2)O_(3)即可稳定存在于钢中并在钢液降温过程中成为TiN的凝固核心,促使TiN夹杂分布弥散,减少了大尺寸TiN的生成.

基于镁处理的含硫齿轮钢硫化物形态控制

为考察镁变质夹杂物对含硫齿轮钢中硫化物形态的控制效果,对加硫40Cr钢进行镁处理,结合热力学分析,解析了冶炼和轧制过程夹杂物的演变行为。研究结果表明,金属镁添加到钢液中后,可将钢中Al_(2)O_(3)夹杂变质为弥散分布的MgAl_(2)O_(4)夹杂;在凝固过程中,变质后的MgAl_(2)O_(4)夹杂可以作为硫化锰的析出核心形成复相夹杂;在轧制过程中,核心的MgAl_(2)O_(4)可进一步发挥骨架作用而抑制周边硫化锰的延展,有效降低了硫化锰的长径比,预期有利于齿轮钢切削性能和机械性能的改善。研究结果还表明,欲充分发挥MgAl_(2)O_(4)的骨架作用,需要保证钢中具有足够高的溶解镁含量使Al_(2)O_(3)充分变质,并促使MgAl_(2)O_(4)具有合适的粒度和数量,以成为控制硫化锰析出与变形的有效核心。