Microstructures and mechanical properties of Mg-Al-Sm series heat-resistant magnesium alloys

The microstructures and phase compositions of the as-cast and die-cast Mg-6.02Al-1.03 Sm, Mg-6.05Al-0.98Sm-0.56 Bi and Mg-5.95Al-1.01Sm-0.57 Zn alloys were investigated. Meanwhile, the tensile mechanical and flow properties were tested. The results show that the as-cast microstructure of Mg-6.02Al-1.03 Sm alloy is composed of δ-Mg matrix, discontinuous δ-Mg17Al12 phase and small block Al2 Sm phase with high thermal stability. Rod Mg3Bi2 phase precipitates when Bi is added, while the added metal Zn dissolves into δ-Mg matrix and δ-Mg17Al12 phase. The as-cast alloys exhibit the excellent tensile mechanical property. The tensile strength（δb） and elongation（δ） can reach 205-235 MPa and 8.5%-16.0% at ambient temperature, respectively. Meanwhile, they can also exceed 160 MPa and 14.0% at 423 K, respectively. The die-cast microstructures are refined obviously, and meanwhile the broken second phases distribute dispersedly. The die-cast alloys exhibit better tensile mechanical properties with the values of δb and δ of 240-285 MPa and 8.5%-16.5% at ambient temperature, respectively, and excellent flow property with the flow length of 1870-2420 mm. The die-cast tensile fractures at ambient temperature exhibit a typical character of ductile fracture.

Semisolid die forging process,microstructures and properties of AZ31 magnesium alloy mobile telephone shells

A semisolid slurry of AZ31 magnesium alloy was prepared by vibrating wavelike sloping plate process,and the semisolid die forging process,microstructures,and properties of the magnesium alloy mobile telephone shell were investigated.The semisolid forging process was performed on a YA32-315 four-column universal hydraulic press.The microstructures were observed by optical microscopy,the hardness was analyzed with a model 450SVD Vickers hardometer,the mechanical properties was measured with a CMT5105 tensile test machine,and the fractograph of elongated specimens was observed by scanning electron microscopy （SEM）.The results reveal that with the increase of die forging force,the microstructures of the product become fine and dense.A lower preheating temperature and a longer dwell time are favorable to the formation of fine and dense microstructures.The optimum process conditions of preparing mobile telephone shells with excellent surface quality and microstructures are a die forging force of 2000 kN,a die preheating temperature of 250℃,and a dwell time of 240 s.After solution treatment at 430℃ and aging at 220℃ for 8 h,the Vickers hardness is 61.7 and the ultimate tensile strength of the product is 193MPa.Tensile fractographs show the mixing mechanisms of quasi-cleavage fracture and ductile fracture.

Influence of semisolid forging ratio on the microstructure and mechanical properties of Ti14 alloy

The present work is focused on the microstructure and mechanical properties of Ti14 alloy with different semisolid deformation ratios during forging tests. The results revealed that the forging ratio had a significant effect on the precipitation of the alloy. Fewer plate-shaped Ti2Cu tended to precipitate on grain boundaries with higher forging ratios, and finally the plate-shaped Ti2Cu formed precipitate-free zones along grain boundaries with a forging ratio of 75%. The precipitation on grain boundaries was found to be controlled by a peritectic reaction. Large forging ratios accelerated the extrusion of liquid and resulted in less liquid along the prior grain boundaries, which reduced the peritectic precipitation in this region and formed precipitate-free zones during re-solidification. In addition, increasing the forging ratio could accelerate dynamic recrystallization, which is favorable for improving the semisolid formability. The tensile ductility increased with increasing forging ratio, and a mixed fracture mode, involving both cleavage and dimple fracture, was observed after forging with a forging ratio of 75%, which along grain boundaries during semisolid processing. is attributed to the presence of precipitate-free zones formed

Effect of heat treatment on microstructures and mechanical properties of sand-cast Mg-10Gd-3Y-0.5Zr magnesium alloy

The microstructure, mechanical properties and fracture behavior of sand-cast Mg-10Gd-3Y-0.5Zr alloy （mass fraction,%） under T6 condition （air cooling after solid solution and then aging heat treatment） were investigated. The optimum T6 heat treatments for sand-cast Mg-10Gd-3Y-0.5Zr alloy are （525 ℃, 12 h＋225 ℃, 14 h） and （525 ℃, 12 h＋250 ℃, 12 h） according to age hardening curve and mechanical properties, respectively. The ultimate tensile strength, yield strength and elongation of the Mg-10Gd-3Y-0.5Zr alloy treated by the two optimum T6 processes are 339.9 MPa, 251.6 MPa, 1.5%and 359.6 MPa, 247.3 MPa, 2.7%, respectively. The tensile fracture mode of peak-aged Mg-10Gd-3Y-0.5Zr alloy is transgranular quasi-cleavage fracture.

Effect of trace Ni addition on microstructure,mechanical and corrosion properties of the extruded Mg-Gd-Y-Zr-Ni alloys for dissoluble fracturing tools

Magnesium alloys,a novel functional material for the fabrication of fracturing tools,are being paid more and more attentions recently due to their relatively high mechanical properties and fast dissolubility ability after fracturing.In this study,the novel extruded Mg-10Gd-3Y-0.3Zr-xNi alloys will be reported and their microstructure,mechanical and corrosion behaviors will be also studied.The results show that Ni contents influence phase precipitation behaviors.With adding 0.2 wt%Ni,a large amount of Zr_(7)Ni_(10)phases will be precipitated insidesα-Mg matrix,directly leading to degradation of strength and large corrosion rate.With further increasing Ni contents,the precipitation phases can be changed from Mg_(5)RE to 18R-LPSO structure,resulting in higher mechanical properties and faster corrosion rate.Moreover,adding Ni element also change the texture orientation by influencing the precipitation behavior of the alloys.The alloys invented in this paper have attained the highest compressive and tensile properties among all the reported dissoluble magnesium alloys.This work is beneficial in understanding the role of Ni in the magnesium alloys and provides more materials alternatives for the fabrication of dissoluble fracturing tools.

Effects of Cu addition on microstructureand mechanical properties of as-cast Mg-6Znmagnesium alloy

The application of Mg-Zn binary alloys is restricted due to their developed dendritic microstructure and poor mechanical properties. In this study, an alloying method was used to improve the mechanical properties of Mg-Zn alloy. The Mg-6Zn magnesium alloys microalloyed with varying Cu content(0, 0.8, 1.5, 2.0 and 2.5wt.%) were fabricated by permanent mould casting, and the effects of Cu content on the microstructure and mechanical properties of as-cast Mg-6Zn alloys were studied using OM, SEM, XRD and tensile tests at room temperature. The obtained results show that the addition of Cu not only can refine the grains effectively, but also can modify the eutectic morphology and improve the mechanical properties of the alloys. The main phases of the studied alloys include α-Mg, MgZn_2, Mg_2Cu and CuMgZn. When the content of Cu exceeds 0.8wt.%, Mg_2Cu phase appears. Meanwhile, the eutectic morphology is modified into dendritic shape or lamellar structure, which has an adverse effect on the tensile properties. Furthermore, among the investigated alloys, the alloy containing 0.8% Cu shows an optimalultimate tensile strength of 196 MPa, while the alloy with 1.5wt.% Cu obtains an excellent elongation of 7.22%. The experimental alloys under different Cu contents show distinguishing fracture behaviors: the fracture of the alloy with 0.8wt.% Cu reveals a mixed mode of inter-granular and quasi-cleavage, while in other investigated alloys, the fracture behaviors are dominated by cleavage fracture.

Effect of Zn content on microstructure, mechanical properties and fracture behavior of Mg-Mn alloy

The optical microscope, scanning electron microscope and universal testing machine are used to investigate the effect of Zn content on the microstructure, mechanical properties and fracture behavior of Mg- Mn-Zn alloy. The results indicate that fine （Mg, Mn, AI）-containing phases are distributed uniformly in the Mg-Mn alloy matrix, while small amount of （Mg, Zn）-containing phases are formed in the matrix and the grain boundary becomes coarse when 1wt.% Zn is added. As the Zn content increases, the amount of （Mg, Zn）-containing phases increases, and the grain boundary becomes coarser. When the Zn content is between 3wt.%-5wt.%, slender （Mg, Zn）-containing phases precipitate at the grain boundary. The addition of Zn could reduce the grain size and enhance the mechanical properties of the alloy matrix, and both of the effects can be enhanced by increasing the Zn content further more. When the Zn content is more than 3wt.%, grain size stops decrease, the strength cannot be improved any more and elongation decreases significantly. The fracture behavior of Mg-Mn alloy appears to be cleavage fracture, and transforms into quasi-cleavage fracture as Zn is added. When Zn content exceeded 3wt.%, large amount of （Mg, Zn）-containing phases appear on the fracture face, and act as the crack sources.

Effects of Gd on microstructure and mechanical property of ZK60 magnesium alloy

Microstructures and phase compositions of as-cast and extruded ZK60-xGd （x=0-4） alloys were investigated. Meanwhile, the tensile mechanical property was tested. With increasing the Gd content, as-cast microstructure is refined gradually. Mg-Zn-Gd new phase increases gradually, while MgZn2 phase decreases gradually to disappear. The second phase tends to distribute along grain boundary by continuous network. As-cast tensile mechanical property is reduced slightly at ambient temperature when the Gd content does not exceed 2.98%. After extrusion by extrusion ratio of 40 and extrusion temperature of 593 K, microstructure is refined further with decreasing the average grain size to 2 μm for ZK60-2.98Gd alloy. Broken second phase distributes along the extrusion direction by zonal shape. Extruded tensile mechanical property is enhanced significantly. Tensile strength values at 298 and 473 K increase gradually from 355 and 120 MPa for ZK60 alloy to 380 and 164 MPa for ZK60-2.98Gd alloy, respectively. Extruded tensile fractures exhibit a typical character of ductile fracture.

Age hardening,fracture behavior and mechanical properties of QE22 Mg alloy

The microstructure,mechanical properties and fracture behavior of an as-received QE22 alloy have been investigated under different thermal conditions,including solution treated(ST),under aged(UA),peak aged(PA)and over aged(OA)conditions.A significant increase in hardness of 27%,yield strength of 60%and ultimate tensile strength of 19%was observed in peak aged sample as compared to solution treated sample.The improvements of mechanical strength properties are mainly associated with the metastable λ and β′precipitates.Grain growth was not observed in the ST samples after subjecting to UA and PA treatments due to the presence of eutectic Mg_(12)Nd particles along the grain boundaries.In over aged sample,significant grain growth occurred because of dissolution of eutectic phase particles.Different natures of crack initiation and propagation were observed under different thermal conditions during tensile testing at room temperature.The mode of failure of solution treated sample is transgranular,cleavage and twin boundary fractures.A mixed mode of transgranular,intergranular,cleavage and twin boundary failure is observed in both peak aged and over aged samples.

Microstructure evolution and mechanical properties of rheo-squeeze casting AZ91-Ca alloy during heat treatment

The rheo-squeeze casting(RSC)process is a newly-developed casting process for high-performance components.In order to further improve the mechanical properties of magnesium alloys,AZ91-2wt.%Ca(AZX912)alloy was prepared by the RSC process and then subjected to heat treatment.The microstructure evolution and mechanical properties of AZX912 alloy during heat treatment were investigated.It was found that during solid solution treatment at 410°C,β-Mg_(17)Al_(12) phase with low melting point dissolves intoα-Mg matrix,while the connected network-like Al_2Ca phase with high melting point tends to separate gradually,and the tips of Al_2Ca phase is partially spheroidized.With the increase of solid solution time,the yield strength(YS)of AZX912 alloy decreases gradually while the ultimate tensile strength(UTS)and elongation to failure(E_f)increase continuously.Isothermal ageing at 225°C promotes the precipitation ofβ-Mg_(17)Al_(12) phase in the matrix of AZX912 alloy.The hardness reaches the peak after ageing for 96 h and the increase in hardness is about 24.8%.The precipitation ofβ-Mg_(17)Al_(12) phase during ageing treatment is beneficial to YS but harmful to E_f.The mechanism of microstructure evolution during heat treatment and its effect on mechanical properties are discussed.

Microstructure and property of rheocasting AZ91 slurry produced via ultrasonic vibration process

The microstructure and mechanical properties of rheocasting AZ91 magnesium alloy were investigated. The semisolid slurry of this alloy was prepared by ultrasonic vibration （USV） process and then shaped by high pressure diecasting （HPDC）. The results show that fine and spherical a-Mg particles were obtained by USV at the nucleation stage, which was mainly attributed to the cavitation and acoustic streaming induced by the USV. Extending USV treatment time increased the solid volume fraction and average particle size, the shape factors were nearly the same, about 0.7. Excellent semisolid slurry of AZ91 magnesium alloy could be obtained within 6 rain by USV near its liquidus temperature. The rheo-HPDC samples treated by USV for 6 min had the maximum ultimate tensile strength and elongation, which were 248 MPa and 7.4%, respectively. It was also found that the ductile fracture mode prevailed in the rheocasting AZ91 magnesium alloy.

镁合金倾斜薄壁电弧熔丝增材制造工艺与力学性能研究

电弧增材制造是一种以金属丝材为填充材料,以电弧作为热源的新型制造技术,易于制造大型复杂零件。通过往复单向路径实验,发现单向路径制造的斜壁有更好的形貌,飞溅少且表面光滑,并在有限元软件中建立了往复、单向制造路径仿真模型并求解,仿真得到单向路径沉积温度267.4℃,沉积热应力357.4 MPa,往复路径沉积温度307.0℃,沉积热应力420.4 MPa,发现单向路径的热积累和热应力更低;以单向制造路径,采用电弧增材制造技术制备AM11,AM12,AM21三种不同斜率的斜壁样件,研究其组织和力学性能。结果表明:AM11,AM12,AM21的晶粒尺寸分别为35,39,42μm;AM21薄壁晶粒中析出相β-Mg17Al12比另外两种样品多且分布均匀、拉伸断口的韧窝更大且更多;AM21与AM11显微硬度在81.5HV左右,均高于AM12的73.1HV;且AM21的斜壁样件的水平、竖直方向抗拉强度为255.7,224.4 MPa,屈服强度为103.8,96.0 MPa,伸长率达到13.1%,8.2%,抗拉强度与伸长率均大于AM11和AM12,但屈服强度接近。AM21斜率薄壁具有更好的强度和塑性,验证了镁合金电弧增材制造的斜壁越接近垂直,其强度、塑性等力学性能越好。

Rheo-diecasting of AZ91D magnesium alloy

A rheo-diecasting process （RDC） was investigated for semisolid processing of an AZ91D magnesium alloy. The results of the RDC samples in as-cast state indicate that the microstructure of primary α-Mg particles has a fine size, nearly spherical morphology, and uniform distribution throughout the components. Due to the advanced microstructure and reduced level of defects, the RDC AZ91D Mg alloy exhibits an apparent improvement in mechanical properties. The quantitative metallographic investigations reveal that increasing the intensity of forced convection during the slurry preparation results in a promoted nucleation and reduced volume fi-acfion of the primary phase solidified in the slurry maker.

Ca微合金化对Mg-8Gd-1Er-1Zn-0.5Zr-xCa合金显微组织和力学性能的影响

本文研究了Ca微合金化对铸态及锻造态Mg-8Gd-1Er-1Zn-0.5Zr-xCa(x=0.1,0.3,0.5,质量分数,%)合金的显微组织和力学性能的影响规律。结果表明:随合金中Ca含量的增加,合金第二相转变过程为:非连续的鱼骨状Mg_(3)Gd相→粗化的Mg_(3)Gd相+Mg_(5)Gd相+Mg_(2)Ca相→少量Mg_(3)Gd相+Mg_(5)Gd相+Mg_(2)Ca相+块状LPSO相,合金晶粒尺寸减小,第二相体积分数增加,力学性能提高。添加0.5%Ca的合金抗拉强度、屈服强度和伸长率最高,分别为241.0 MPa、149.2 MPa和5.7%。固溶处理后,晶界处形成LPSO相,且其体积分数随合金中Ca含量的增加而增加,促进了合金在后续锻造过程中发生动态再结晶,基面织构强度随之增加,基面Schmid因子随之降低。当合金中Ca含量为0.5%时,合金锻后力学性能最佳,其抗拉强度、屈服强度和伸长率分别达到344.6 MPa,274.5 MPa和8.1%。分析认为基面织构增强和晶界强化是锻造态合金力学性能提高的主要原因。

Microstructural and mechanical response of ZK60 magnesium alloy subjected to radial forging

Radial forging(RF)is an economical manufacturing forging process,in which four dies arranged radially around the workpiece simultaneously act on the workpiece with high-frequency radial movement.In this study,a ZK60 magnesium alloy step-shaft bar was processed under different accumulated strains by RF at350℃.The deformation behavior,microstructure evolution,and mechanical responses of this bar were systematically investigated via numerical simulations and experiments.At the early deformation stage of forging,the material undergoes pronounced grain refinement but an inhomogeneous grain structure is formed due to the strain gradient along the radial direction.The grains in different radial parts were gradually refined by increasing the RF pass,resulting in a bimodal grained structure comprising coarse(~14.1μm)and fine(~2.3μm)grains.With the RF pass increased,the initial micro-sizeβ-phases were gradually crushed and dissolved into the matrix mostly,eventually evolving to form a higher area fraction of nano-sized Zn2 Zr spheroidal particles uniformly distributed through the grain interior.The texture changed as the RF strain increased,with the c-axes of most of the deformed grains rotating in the RD.Additionally,excellent mechanical properties including higher values of tensile strengths and ductility were attained after the three RFed passes,compared to the as-received sample.

电弧增材制造AZ31镁合金组织与力学性能分析

针对镁合金在轻量化结构件领域的应用前景,采用基于MIG焊的电弧增材制造工艺开展了两组不同路径的AZ31镁合金增材实验,并对其微观组织和力学性能进行了分析。结果表明:增材构件相较于原始焊丝的化学成分无较大变化;单道次多层往复堆积路径相较于多道次多层堆积路径,更易制得表面更为平整,内部更为致密的构件,其屈服强度为77.3 MPa,抗拉强度为235 MPa,达到原始焊丝75%的力学性能水平,平均显微硬度为52.7HV,断后伸长率最高达到了27%;增材构件拉伸断裂方式为韧性断裂,并在多道次多层往复堆积构件断口处发现其内部存在气孔。验证了电弧增材制造AZ31镁合金工艺的可行性。

多向锻造工艺对AZ80镁合金显微组织和力学性能的影响

通过多向锻造工艺制备出了组织均匀、晶粒尺寸为1-2 μm的AZ80镁合金锻坯．经7个道次锻压,材料硬度、屈服强度和抗拉强度达到最大,分别为87．3 HB,258．78 MPa和345．04 MPa,是锻前试样硬度的1．43倍、强度的2倍;伸长率在6个道次达到最大,为7．85％,是锻前的2．45倍．多向锻造工艺下,材料内部易形成交错变形带,有利于组织细化．形变诱导晶粒细化是主要的晶粒细化机制．晶粒细化过程存在一临界应变量εc(2≤εc≤2．4),当实际应变量εx超过临界应变量εc 时,材料基本为动态再结晶细晶组织,进一步细化变得困难．铸态试样室温拉伸断口为准解理断裂加少量剪切断裂,锻后试样断口出现大量细小韧窝．随应变量的增加,韧窝数目增多,分布趋向均匀,材料延性增大,

多向锻造ZK60镁合金组织和性能的均匀性

采用空气锤对ZK60镁合金进行多向锻造变形,研究锻坯的组织演变以及组织和性能均匀性。结果表明,锻锤与锻坯之间摩擦力的作用造成不均匀变形,使锻坯芯部的实际变形量大于边部的。累积应变∑Δε=3.3时,锻坯芯部组织为蜂窝状粗大再结晶组织和岛状细小再结晶组织,而边部组织则由蜂窝状粗大再结晶组织和呈岛状分布的孪晶组成;其抗拉强度从边部到芯部逐渐降低,而伸长率则由边部向芯部逐渐升高。锻坯力学性能存在一定的各向异性,但锻坯各方向抗拉强度在310.6-323.9 MPa之间,伸长率在21.9%-29.7%之间,表明该工艺可以有效地避免强烈的各向异性,是制备高性能变形镁合金的理想工艺。

AZ61镁合金挤锻复合成形组织与力学性能

采用铸坯挤压制备具有最终试样二维几何特征的AZ61镁合金预成形坯材,经过一次纵向模压制备了近终成形的拉伸试样,对试样进行了组织和拉伸性能检测。实验结果表明：在挤锻复合成形工艺过程中,材料组织经过变形与再结晶,晶粒尺寸从铸态的121μm细化为挤压态的8-15μm,锻压后进一步细化到2-5μm。经历了挤锻复合成形后,材料的室温抗拉强度、屈服强度、伸长率和硬度分别达到315.2MPa2、27.4MPa和20.5%,比铸态分别提高了42.4%、76%和71%;拉伸失效断口也从铸态的准解理断裂过渡为模压后以韧性断裂为主的特征。

镁合金锻造研究综述

讨论了镁合金锻造研究的现状与进展,介绍了常用锻造镁合金种类、镁合金锻造特点、影响镁合金锻造的因素以及锻造过程中组织演变和力学行为,最后展望了锻造镁合金的发展方向及应用前景。