ICP-AES Determination of Germanium in GdSiGe Series Alloys as Magnetic Refrigeration Material

The ICP-AES method for the determination of Ge in GdSiGe series alloys was studied.As the three main elements in the alloys,Gd,Si,and Ge differ greatly from each other in chemical properties,it was difficult to pretreat the sample.Two decomposition methods were compared,and a mixture of HNO3＋HF was used to decompose the sample and the effect of the HF amount on the sample decomposition was examined.The adsorption effect of GdF3 on Ge was discussed.Three GdSiGe series alloy samples were analyzed,and the RSDs of this method were in the range of 0.85%～2.66%.

Influence of Al content on machinability of AZ series Mg alloys

Influence of A1 content on the machinability of AZ series cast Mg alloys was investigated. In order to evaluate the machinability of the alloys, measurements of the cutting forces during turning operations and surface roughness were carried out as well as considering the microstructure and tensile properties. The results show that maximum tensile properties are observed with 2% （mass fraction） A1 addition to Mg. As the A1 content of the alloy increases above 2%, the cutting forces tend to reduce along with the ductility owing to the grain boundary precipitation of intermetallic phase （fl-Mgl7All2）. Cutting forces are able to increase as the cutting speed increases for all the alloys studied, and it＇s attributed to flank built up at the tip of the cutting tool during machining.

Combustion synthesis of fine TiFe series alloy powder by magnesothermic reduction of ilmenite

Fine TiFe series alloy powder was fabricated by magnesothermic reduction of ilmenite as main raw material.Adiabatic temperature of the FeTiO_(3)-Mg system was studied through thermodynamic analysis.Meanwhile,the characteristics of TiFe series alloy were described by XRD,SEM and grading analysis.It is shown that combustion synthesis of the FeTiO_(3)-Mg system can carry out due to its strong exothermic reaction through adiabatic temperature calculate.Ultrafine TiFe series alloy powder after leached for 5 h has reasonable phases and morphology with the particle distribution of 0.2 to 1μm.It indicates that in-situ magnesothermic reduction of natural ilmenite is a feasible way to fabricate ultrafine powder with a relatively lower cost.

Strengthening-toughening of 7xxx series high strength aluminum alloys by heat treatment

The effects of stepped solution heat treatments on the dissolution of soluble remnant constituents and mechanical properties of 7055 aluminum alloy were investigated. It was shown that a suitable pretreatment at lower temperature can enable complete dissolution of the constituent particles in 7055 alloy without overheating by subsequent high temperature solution treatment. This in turn increased the tensile strength and fracture toughness of 7055 alloy to 805 MPa and 41.5 MPa·m 1/2 respectively, with approximately 9% tensile elongation. The near solvus pre precipitation following after high temperature solution treatment was also studied on 7055 aluminum alloy. The effect of the pre precipitation on the microstructure, age hardening and stress corrosion cracking of 7055 alloy was investigated. The optical and transimission electron microscopy observation show that the near solvus pre precipitation can be limited to grain boundary and enhance the discontinuity of grain boundary precipitates in the subsequent ageing. The stress corrosion cracking resistance of aged 7055 alloy can be improved via the pre precipitation with non deteriorated strength and plasticity.

Influence of aluminum content on machinability of AS series cast magnesium alloys

The influence of Al content on machinability of AS series cast Mg alloys was studied. The assessment of machinability of Mg alloys was performed by measuring the cutting forces and surface roughness. The microstructure and the tensile properties were also studied. The results reveal that cutting forces are increased with the increase of the Al content. Surface roughness and mechanical properties are the highest for AS91 Mg alloy. It is assumed that the main mechanism, which has an influence on the mechanical properties, is the presence of intermetallic phases(Mg2Si and Mg17Al12). Cutting forces increase with the increase of the cutting speed in machining of all Mg alloys. These measured data are in accordance with the mechanical properties of the machined alloys.

Microstructure and mechanical properties of as-extruded Mg-Sn-Zn-Ca alloy with different extrusion ratios

The effect of extrusion ratio on microstructure and mechanical properties of as-extruded Mg-6Sn-2Zn-1Ca （TZX621）（mass fraction, %） alloy was investigated. It is found that incomplete dynamic recrystallization （DRX） took place in as-extrudedTZX621 alloy. As the extrusion ratio was increased from 6 to 16, both fraction of un-DRXed grains and average size of DRXedgrains in as-extruded TZX621 alloy decreased and the basal texture was weakened. Coarse CaMgSn phase was broken into particlesand fine Mg2Sn phase precipitated from α-Mg matrix during hot extrusion. Yield strength, ultimate tensile strength and elongation ofas-extruded TZX621 alloy with extrusion ratio of 16 reached 226.9 MPa, 295.6 MPa and 18.1%, which were improved by 36.0%,17.7% and 13.5%, respectively, compared to those of as-extruded TZX621 alloy with extrusion ratio of 6.

On the improved tensile strength and ductility of Mg-Sn-Zn-Mn alloy processed by aging prior to extrusion

This study investigated the influence of aging prior to extrusion(APE)on the tensile strength and ductility of as-extruded Mg-8.32Sn-1.85Zn-0.17Mn alloy.Results demonstrated that APE treatment dramatically increased the volume fraction of recrystallized grains,thereby decreasing the grain size of the as-extruded alloy.This phenomenon was primarily attributed to the particle-stimulated nucleation and pinning effect induced by large amounts of small Mg 2 Sn precipitates produced by the APE treatment and dynamic precipitation.The tensile yield strength increased from 242.4 MPa to 256.5 MPa after APE treatment.The improved tensile strength can be attributed to the enhanced grain boundary strengthening and precipitation strengthening.The ductility of the as-extruded alloy also markedly increased from 7.1%to 13.5%after the APE treatment.The improved ductility of APE alloy was attributed to the texture randomization,the activity of pyramidal<c+a>slip and the suppressed formation of{10-11}contraction twins and coarse Mg 2 Sn phases.

A systematic investigation of secondary phase dissolution in Mg-Sn alloys

As-cast Mg-Sn alloys(3,6,and 9 wt%Sn)were solution treated at 653,703 and 753 K(380,430 and 480℃)for 1,4,8,12 and 24 h to determine the variation of secondary phase with respect to Sn content,temperature and time.Mg-3 wt%Sn exhibits Mg2Sn dissolution at all solution treatment temperatures whereas Mg-6 and 9 wt%Sn alloy displays Mg2Sn reprecipitation and dissolution depending on the heat treatment temperature.In addition,a combined mathematical model that predicts the secondary phase dissolution and solute redistribution as a function of temperature and time is presented in this work.This model is a significant improvement compared to the previous studies where the dissolution and homogenization processes are considered independently.The effect of grain size and solute mobility upon the dissolution and homogenization kinetics is discussed as well.

Microstructures and tensile properties of as-extruded Mg-Sn binary alloys

The microstructure and mechanical properties of Mg-xSn （x-3, 7 and 14, mass fraction, %） alloys extruded indirectly at 300 ℃ were investigated by means of optical microscopy, scanning electron microscopy and tensile test. The grain size of the a-Mg matrix decreases from 220, 160 and 93 μm after the homogenization treatment to 28, 3 and 16 μm in the three alloys after extrusion, respectively. The results show that the grain refinement is most remarkable in the as-extruded Mg-7Sn alloy. At the same time, the amount of the Mg2Sn particles remarkably increases in the Mg-7Sn alloy with very uniform distribution in the a-Mg matrix. In contrast, the Mg2Sn phase inherited from the solidification with a large size is mainly distributed along grain boundary in the Mg-14Sn alloy. The tensile tests at room temperature show that the ultimate tensile strength of the as-extruded Mg-7Sn alloy is the highest, i.e., 255 MPa, increased by 120% as compared with that of as-cast samples.

第三组元对Mg-Sn合金铸态组织与力学性能的影响

利用光学显微镜、扫描电子显微镜和X射线衍射仪分析Mg-3.52Sn-xM和Mg-6.54Sn-xM(M=Al,Zn,Nd,Gd)合金的铸态组织和相组成,测试其拉伸力学性能。结果表明:在Mg-3.52Sn合金中分别添加0.91%(质量分数,下同)Al和1.03%Zn后,粗大树枝晶有所细化,小块状Mg2Sn相极少;分别添加0.92%Nd和1.10%Gd后,树枝晶明显弱化,出现较多的小块状或细短杆状化合物Mg-Sn-Nd和Mg-Sn-Gd。在Mg-6.54Sn合金分别添加0.93%Al和1.08%Zn后,树枝晶明显细化,原先趋于连续网状分布的Mg2Sn相有所破碎;分别添加0.86%Nd和0.74%Gd后,树枝晶亦明显弱化,Mg2Sn相已完全破碎成小块状并呈弥散分布或出现明显破碎,同样出现较多的小块状或细短杆状化合物Mg-SnNd和Mg-Sn-Gd。在Mg-3.52Sn和Mg-6.54Sn二元合金中添加约1%的Al和Zn能有效提高其室温和高温拉伸力学性能,而分别添加约1%的Nd和Gd则不能有效提高其室温和高温拉伸力学性能,且Nd的弱化效果更明显。

A comparative study on corrosion of Mg-Al-Si alloys

Corrosion behavior of various Mg-Al-Si alloys(AS11,AS21,AS41,AS61and AS91series),cast under the same coolingconditions and controlled alloying composition,was investigated systematically.Optical microscopy and scanning electronmicroscopy were used for microstructural examinations.The corrosion behavior was evaluated by immersion tests andpotentiodynamic polarization measurements in3.5%NaCl solution.The results from both immersion tests and the potentiodynamicpolarization measurements showed that marginal improvement in corrosion resistance was observed with2.0%Al(mass fraction)containing alloy(AS21)whereas Al addition above2.0%(AS41,AS61and AS91)deteriorated the corrosion resistance which wasattributed toβphase,acting as cathode,and the interruption of continuity of the oxide film on the surface of the alloys owing tocoarsenedβand Mg2Si phases.

Comparative study on corrosion behaviors of Mg-Al-Zn alloys

A comparative study on corrosion behaviors of various Mg-Al-Zn alloys(AZ21,AZ41,AZ61 and AZ91 series,cast under same cooling conditions and controlled alloying composition)was carried out.Scanning electron microscopy(SEM)and X-ray diffraction(XRD)were used for microstructural examinations.The corrosion behaviors were evaluated by immersion tests and potentiodynamic polarization measurements in 3.5%NaCl solution.The results showed that the influence of Al addition on corrosion resistance was more pronounced up to 4%(i.e.AZ41)above which its influence was at less extent.The deterioration of the corrosion resistance of the alloys,at higher Al contents,was attributed to the amount and morphology ofβ-Mg17Al12 intermetallics and the interruption of continuity of the oxide film on the surface of the alloys owing to coarsenedβintermetallics.

The Stretch, Limit and Path Forward for Particle Reinforced Metal Matrix Composites of 7075 Al-Alloys

Al-based metal matrix composites [MMCs] have been the research interest of a wide spectrum of material scientists throughout the world for some over two decades now. The present paper has chosen one alloy system namely the 7xxx series and from an extensive literature review concluded that since the beginning of the new millennium nothing note worthy has been added to the knowledge already gained in the last quarter of the last century except confirm the earlier findings that MMCs if properly fabricated by choosing the processing route and with appropriate size and volume fraction of dispersoids can improve most of the mechanical, corrosion and wear resistant properties of the base alloy. The author’s own research activities using this alloy system for making MMCs that include attempts to improve upon the properties by making composites, ageing and also secondary processing have been included. An attempt has been made to establish the stretch to which improvement is possible in the alloy system by making composites and trying all other routes known for meaningful improvement in properties. Further, the way forward for such particulate composites has been drawn to realise the material scientists’ dream of seeing such MMCs as engineering components. For this, the areas which now need research include mass production of composites, focus on its machining, joining, processing as also reduction in the size of dispersoids are some of the areas that have been identified and discussed in the paper.

Effect of microelements on microstructures and properties of Al-1·2Mg-1·3Si-0·6Cu-0·3Mn alloy

The effects of impurity element of Fe and microelements of Zn, Cr and Ti on the constituents, dispersoids, grain size, mechanical properties and formability of Al-1.3Mg-1.2Si-0.6Cu-0.3Mn alloy were investigated in the present work by analyzing microstructures, phase composition, mechanical tests. The results indicated that with the increase of Fe content, the insoluble constituents increased, and the mechanical properties and r15 of alloy sheets debased, which can be recovered by the addition of microelements Zn, Cr and Ti. Al-1.3Mg-1.2Si-0.6Cu-0.3Mn alloy sheets in the T4 temper are difficult to strengthen with paint-bake treatment in automobile factory.

Ordered Sn distribution adjacent to the precipitate-matrix interface in a Mg-9.8wt.%Sn alloy

The major interface betweenβ-Mg_(3)Sn precipitate plate and theα-Mg matrix in a Mg-9.8wt.%alloy has been investigated using aberrationcorrected scanning transmission electron microscopy and first-principles calculations.It is found that Sn atoms orderly distribute in the single layer of theα-Mg matrix immediately adjacent to the broad surface ofβat the early stage of ageing.These Sn atoms substitute Mg atoms located at the centers of equilateral triangles constituted by three Mg columns in the outmost layer ofβ.First-principles calculations suggest that the ordered Sn distribution is energetically favored and it not only decreases the interfacial energy of theβ-matrix interface but also hinders the occurrence of 1/3<01■0>αshear that thickens theβplate.

7000系高强铝合金微观组织结构对应力腐蚀行为和机制影响的研究进展

7000系(Al-Zn-Mg-Cu)高强铝合金是铝合金中强度最高的系列之一,应力腐蚀开裂(SCC)是影响其服役安全稳定性的关键因素。综述了应力腐蚀开裂的阳极溶解机制和氢致开裂(HIC)机制,总结了7000系铝合金中的组织结构对合金SCC行为及机制的影响;从合金化学成分、热处理、预应变、表面处理等方面对SCC敏感性的影响出发,论述了不同组织结构对SCC行为的影响。提出了降低7000系高强铝合金SCC敏感性的重点研究方向:通过优化合金元素、使用新型的热处理工艺和表面处理技术等方法合理调控合金的微观组织结构,进而延长合金的使用寿命,使材料受到更好地保护。

CoCrMo和CoCrMoW合金的组织结构、力学性能及在小牛血清溶液中的腐蚀摩擦学性能研究

为了明确CoCrMo和CoCrMoW合金在小牛血清溶液中的腐蚀摩擦行为和耐腐蚀磨损机制,使用真空熔炼技术制备CoCrMo和CoCrMoW合金,采用SEM-EDS、TEM、XRD、压缩力学性能试验和腐蚀磨损试验研究2种合金的组织结构、力学和腐蚀摩擦学性能。结果表明:2种合金均由γ-Co和ε-Co组成,且微观组织以等轴晶为主。CoCrMo合金展现出优异的压缩力学性能,且其在小牛血清溶液中具有良好的耐腐蚀性,而CoCrMoW合金出现点蚀。2种合金在小牛血清溶液中具有较好的腐蚀摩擦学性能,其摩擦系数和磨损率分别为0.11~0.21和1.01×10^(-6)~2.46×10^(-6)mm^(3)/(N·m)。随着载荷和频率的增加,2种合金的摩擦系数降低,实时摩擦系数稳定性提高。在低载荷条件下,合金的耐腐蚀磨损性能随频率的增大而增强,其磨损机制以磨粒磨损为主;在高载荷条件下,合金的磨损率随频率的增加而增大,磨粒磨损和腐蚀磨损并存。总体而言,CoCrMo合金的耐腐蚀磨损性能优于CoCrMoW合金,这主要是因为CoCrMo合金具有较好的压缩力学性能和耐腐蚀性能。

敏化处理对AA5083铝合金的腐蚀和应力腐蚀开裂行为的影响

铝镁系合金被广泛用于船舶建造和海洋结构,但是在服役过程中会在晶界析出低腐蚀电位的富镁相,引起环境断裂问题。研究了175℃/100 h敏化处理对铝合金AA5083的Al-Mg相析出行为、晶间腐蚀、电化学行为和应力腐蚀开裂性能的影响,并采用慢应变速率拉伸试验研究敏化前后的应力腐蚀开裂敏感性。结果表明,原始态材料不发生晶间腐蚀和应力腐蚀开裂,而经过敏化处理后,100 nm厚的β'-Al_(3)Mg_(2)或β-Al_(3)Mg_(2)相在晶界析出,导致材料发生严重的晶间腐蚀、电化学腐蚀以及应力腐蚀开裂。铝合金的应力腐蚀开裂行为是在裂纹尖端析出相的阳极溶解以及溶液酸化引发氢脆的协同作用下发生的。

7xxx系铝合金焊接技术研究进展

7xxx系铝合金作为所有系列铝合金强度最高的金属材料,具有优良的综合性能,被广泛应用于各领域中。本文从7xxx系铝合金焊接质量和焊接效率出发,综述了几种常见的7xxx系铝合金焊接技术的发展现状,重点介绍了熔化极惰性气体保护焊(MIG焊)、冷金属过渡焊(CMT)、钨极惰性气体保护焊(TIG焊)等传统电弧焊以及激光焊、电子束焊、搅拌摩擦焊等新型焊接技术的技术特点与应用前景,总结了不同焊接技术相应的优势与不足以及目前各焊接技术急待解决的问题,最后对7xxx系铝合金焊接技术发展前景进行了总结。

高强度7xxx系铝合金热处理调控残余应力研究进展

随着航天装备的不断大型化和轻量化,7xxx系铝合金构件普遍呈尺寸规格大、形状复杂、薄壁弱刚性等结构特点,在加工和使用中易产生强烈的残余应力效应;残余应力的产生会影响加工质量,甚至导致失效。因此,如何有效调控制造过程中的残余应力成为亟待解决的关键难题。总结了航天领域高强度7xxx系铝合金构件残余应力热处理控制技术的研究现状,详细介绍了淬火、冷热循环处理、深冷处理、时效去应力对残余应力的调控效果及作用机制,提出了目前航天高强度7xxx系铝合金残余应力热处理调控的主要问题及发展方向。