Effects of calcium addition on as-cast microstructure and mechanical properties of Mg-5Zn-5Sn alloy

The effects of Ca addition on the as-cast microstructure and mechanical properties of the Mg-5Zn-5Sn (mass fraction,%) alloy were investigated.The results indicate that an addition of 0.5%-1.5% (mass fraction) Ca to the Mg-5Zn-5Sn alloy not only refines the as-cast microstructure of the alloy but also causes the formation of the primary and/or eutectic CaMgSn phases with high thermal stability;an increase in Ca amount from 0.5% to 1.5% (mass fraction) increases the amount and size of the CaMgSn phase.In addition,Ca addition to the Mg-5Zn-5Sn alloy improves not only the tensile properties at room temperature and 150 ℃ but also the creep properties.Among the Ca-containing Mg-5Zn-5Sn alloys,the one added 0.5% (mass fraction) Ca obtains the optimum ultimate tensile strength and elongation at room temperature and 150 ℃,however,the alloy added 1.5% (mass fraction) Ca exhibits the optimum yield strength and creep properties.     

Creep properties and controlled creep mechanism of as-cast Mg-5Zn-2.5Er alloy

The creep behaviors of as-cast Mg-5Zn-2.5Er alloy(mass fraction,%) ,under various applied stresses(50-70 MPa) and creep temperatures(150-200℃) for 100 h,were investigated.The stress exponent n is in the range of 1.5-5.8,and the activation energy Qc is in the range of 28.3-77.1 kJ/mol.With respect to the calculated n and Qc as well as the microstructures after creep,it is suggested that there is a transition region between grain boundary sliding(GBS) dominated creep to dislocation creep mechanism(from n3 to n3) ,arising in the steady-stage creep rate value of 2.89×10-9 s-1.     

Mg-6.3Zn-0.7Zr-0.9Y-0.3Nd镁合金的高温塑性变形行为的热压缩模拟

采用Gleeble-1500热压缩模拟试验机进行压缩实验,研究ZK60(0.9Y+0.3Nd)镁合金在变形温度623～773K、应变速率0.001～1s-1的范围内的变形行为,计算应力指数和变形激活能,并采用Zener-Hollomon参数法构建合金高温塑性变形的本构关系。结果表明:在实验变形条件下,合金的真应力—真应变曲线为动态再结晶型;在实验温度范围内,应力指数随着变形温度的升高而增大,变形激活能随着变形温度和应变速率的增加而增大。对比ZK60合金,ZK60(0.9Y+0.3Nd)合金的变形激活能提高38%。     

Effects of heat treatment on microstructure evolution and mechanical properties of Mg-6Zn-1.4Y-0.6Zr alloy

To investigate the effects of solution temperature and the decomposition of I-phase on the microstructure, phase composition and mechanical properties of as-cast Mg-6Zn-1.4Y-0.6Zr alloy, solution treatment at 440 oC, 460 oC and 480 oC and further aging treatment were conducted on the alloy. The results indicate that the net-like intermetallic compounds(mainly I-phase) dissolve into the α-Mg matrix gradually with the increase of solution temperature from 440 oC to 480 oC. Besides, the I-phase decomposes completely at 480 oC, with the formation of fine W-phase(thermal stable phase) and Mg_7Zn_3 phase. In addition, a great number of fine and dispersive Mg-Zn binary phases precipitate in the α-Mg matrix during the aging treatment. Due to the increase of solute atoms and the precipitation of strengthening phases, such as W-phase and Mg-Zn phases, the optimal strength is obtained after solution treatment at 460 oC for 8 h and aged at 200 oC for 16 h. The yield strength(YS), ultimate tensile strength(UTS) and elongation are 208 MPa, 257 MPa and 3.8%, respectively. Compared with the as-cast alloy, the increments of YS and UTS are 117% and 58%, respectively, while the decrement of elongation is 46%.     

Effects of erbium on microstructure and mechanical properties of as-cast Mg-7Zn-3Al alloy

Mg-7Zn-3Al-xEr(x=0.1,0.4,0.7) magnesium alloys were prepared by permanent mould casting.The effects of rare earth element of erbium on the microstructure and mechanical properties of as-cast Mg-7Zn-3Al alloy at both room temperature and elevated temperatures were investigated with optical microscopy,scanning electron microscopy/energy dispersive X-ray spectroscopy,differential scanning calorimetry,and tensile testing.The results show that the quasi-continuous grain boundary networkedτ(Mg_(32)(Al,Zn)_(49)...     

生物可降解Mg-3Zn-0.8Zr-xMn合金的组织与性能

开发具有良好生物相容性、耐蚀性及综合力学性能的镁合金是当前可降解金属研究领域的重要方向,本文选取具有良好生物相容性的Zn、Zr、Mn合金元素,通过真空熔炼法制备了新型的Mg-3.0%Zn-0.8%Zr-x%Mn(质量分数,x=0,0.1,0.5,1.0,1.5)系列合金。研究了Mn含量变化对该类合金组织、力学性能及腐蚀降解行为的影响。结果表明:Mn的添加可以细化挤压态Mg-Zn-Zr合金的晶粒尺寸;合金的抗拉强度和屈服强度随着Mn含量的增加先升高后降低,在Mn含量为1.0%时,抗拉强度达到255 MPa,电化学及浸泡测试结果表明Mn的添加使合金的自腐蚀电位增加,耐蚀性能升高,当Mn含量为1.0%时,合金耐蚀性能最好;本研究成分范围内Mg-3Zn-0.8Zr-1Mn合金有最佳的综合力学及耐蚀性能。     

Microstructure and mechanical properties of Mg-5.6Li-3.37Al-1.68Zn- 1.14Ce alloy

Mg-5.6Li-3.37Al-1.68Zn-1.14Ce alloy was prepared using vacuum induction melting furnace. The microstructure and phases compostion of as-cast and as-extruded alloys were investigated by optical microscopy, energy dispersive X-ray spectroscopy, scanning electron mocroscopy and X-ray diffraction. The mechanical properties of these alloys were measured with tensile tester. The results indicate that the as-cast alloy is composed of a（Mg） phase and rod-like Al2Ce compound. Al2Ce has the refining effect on the microstructure of alloy. During the extrusion at 523 K, dynamic recrystallization happens in the alloy. The dynamic recrystallization refines the grain size of alloy obviously. The phases are refined clearly after extrusion deformation, and the strength and ductility of the alloy are increased accordingly.     

Mg-5.6Zn-0.7Zr-0.8Nd合金高温塑性变形的热/力模拟研究

采用Gleebe-1500热／力模拟机研究了Mg-5．6Zn-0．7Zr-0．8Nd合金在应变速率为0．1,0．01和0．002s^-^3、变形温度为373—673K,最大变形程度60％条件下的高温塑性变形行为．分析了合金流变应力与应变速率、变形温度之间的关系,计算了高温变形时变形激活能和应力指数,并观察了合金变形过程中显微组织变化情况．结果表明：Mg-5．6Zn-0．7Zr-0．8Nd合金在热变形过程中不同温度下流变应力呈现不同形式,分析可知加工硬化、动态回复和动态再结晶在不同温度和不同应变速率下各自起到了重要的作用,合金变形激活能随应变速率增加而升高．在473K温度以上变形,合金发生明显动态再结晶且动态再结晶晶粒非常细小,晶粒尺寸为5—10μm,从而可明显提高合金的塑性．     

退火处理对预变形Mg-5.3Nd合金压缩强度的影响

通过OM、XRD、SEM、EDS以及室温压缩试验等方法对Mg-5.3Nd合金的金相组织、退火强化行为以及压缩变形机制等进行了研究。结果表明:550℃/8 h固溶处理后,铸态Mg-5.3Nd合金的第二相Mg_(12)Nd基本消除。经预压缩-卸载-再压缩试验,固溶Mg-5.3Nd合金的压缩强度没有明显变化,而预压缩-卸载-退火处理-再压缩试验后,合金的压缩强度明显提高,并获得最佳强化效果的退火工艺为180℃/4 h。原位金相分析发现,未退火试样的再压缩变形机制表现为预变形孪晶的明显长大。而预变形试样退火后,由于钕元素对预变形孪晶的钉扎作用,其再压缩变形机制以新变形孪晶的形成为主。     

Si含量对Mg-8Zn-4Al-0.3Mn镁合金时效过程的影响

采用光学显微镜、扫描电镜(附EDAX能量分散光谱系统)和差示扫描量热仪(DSC)等分析手段研究了不同Si含量(0～1.61wt%)对Mg-8Zn-4Al-0.3Mn(ZA84)合金时效过程的影响。结果表明,合金经固溶处理后显微硬度较铸态下提高了8%左右,其Mg2Si、τ(Mg32(Al,Zn)49)等相基本未溶入基体中。随着ZA84合金中加入Si量的增加,合金的析出相形成激活能呈增加趋势,峰值时效时间由ZA84合金的2h左右推迟至8h左右,析出相粗化时间较ZA84合金推迟4h以上。合金中加入不同含量Si后其峰值时效显微硬度提高幅度为4%～12%。     

Effects of Sm addition on microstructural evolution of Mg-6Zn-0.4Zr alloy during semi-solid isothermal heat treatment

The application of segmental semi-solid thixoforming of magnesium alloys is confined due to the dimensional distinction existing in solid particles of the alloy billet from edge to center zones. In the present study, the effects of Sm addition on the microstructural evolution of Mg-6Zn-0.4Zr and Mg-6Zn-4Sm-0.4Zr alloys by semi-solid isothermal heat treatment were investigated, to obtain optimum semi-solid microstructures for the subsequently thixoforming. The results indicate that the grains of the Sm-bearing alloy are evidently refined and gradually evolve from dendritic to globular and elliptic particles. In addition, the distinctly dimensional effect of the Mg-6Zn-0.4Zr alloy is eliminated with 4% Sm addition; the particle sizes in all zones from center to the edge of the billet are almost identical. With the increment of isothermal heat treatment temperature, the dendritic microstructures completely disappear, and meanwhile, the irregular and globular particles gradually form. The size, morphology and the distribution of solid particles mainly depend on the formation and permeation of the liquid phase in the process of isothermal heat treatment. As the isothermal temperature increases from 570 °C to 610 °C, the average size and shape factor of solid particles of both the alloys with and without Sm addition gradually decrease while the liquid fraction gradually increases.     

Effect of Cu addition on microstructure and properties of Mg-10Zn-5Al-0.1Sb high zinc magnesium alloy

To improve the strength,hardness and heat resistance of Mg-Zn based alloys,the effects of Cu addition on the as-cast microstructure and mechanical properties of Mg-10Zn-5Al-0.1Sb high zinc magnesium alloy were investigated by means of Brinell hardness measurement,scanning electron microscopy (SEM),energy dispersive spectroscopy (EDS),XRD and tensile tests at room and elevated temperatures.The results show that the microstructure of as-cast Mg-10Zn-5Al-0.1Sb alloy is composed of α-Mg,t-Mg32(Al,Zn)49,φ-Al2Mg5Zn2 and Mg3Sb2 phases.The morphologies of these phases in the Cu-containing alloys change from semi-continuous long strip to black herringbone as well as particle-like shapes with increasing Cu content.When the addition of Cu is over 1.0wt.%,the formation of a new thermally-stable Mg2Cu phase can be observed.The Brinell hardness,room temperature and elevated temperature strengths firstly increase and then decrease as the Cu content increases.Among the Cu-containing alloys,the alloy with the addition of 2.0wt.% Cu exhibits the optimum mechanical properties.Its hardness and strengths at room and elevated temperatures are 79.35 HB,190MPa and 160MPa,which are increased by 9.65%,21.1% and 14.3%,respectively compared with those of the Cu-free one.After T6 heat treatment,the strengths at room and elevated temperatures are improved by 20% and 10%,respectively compared with those of the as-cast alloy.This research results provide a new way for strengthening of magnesium alloys at room and elevated temperatures,and a method of producing thermally-stable Mg-10Zn-5Al based high zinc magnesium alloys.     

Mg-5Zn-3Al-0.2Mn铸造合金的组织和室温力学性能

研究了砂型铸造Mg-5Zn-3Al-0．2Mn合金的显微组织，发现其主要相组成为δ-Mg基体相和τ（Mg12（Al，Zn）49）化合物相，τ相以半连续网状骨骼形态沿δ相的晶界分布。实验合金中加入少量Sr，Ti，B元素后，合金组织细化，τ相形态转变为断续的短条状或粒状，并且分布更加均匀。在本实验条件下，当炉前加入0．06％Ti、0．012％B、0．1％Sr时，合金的组织形态得到显著改善，合金的室温力学性能最佳。不同温度下对Mg-5Zn-3Al-0．2Mn合金进行的固溶处理实验发现，在335℃固溶17h淬火后，合金的室温抗拉强度和塑性得到了大幅度提高；在343℃固溶17h淬火后，合金组织完全转变为单相固溶体，合金的室温力学性能较好，巩为245MPa，δ为12％。     

Mg-1.5Zn-0.2Ce合金热轧退火后的微观组织及成形性能

通过金相、宏观织构、力学性能和埃里克森杯突实验研究了经450 ℃热轧并在350 ℃退火1 h的Mg-1.5Zn-0.2Ce合金板材的微观组织及成形性能。结果表明：轧制变形能够大大细化晶粒,随着总变形量从80%增加到90%,平均晶粒尺寸由38 μm减小到16 μm,轧向（RD）、斜向（45°）、横向（TD）三个方向的抗拉强度和屈服强度增大,基面织构强度最大值由2.46减小到2.05,r值由0.96减小到0.8,平面各项异性系数Δr由0.19减小到0.01,埃里克森杯突值由5.14增加到5.46。在相同的热处理条件下,总热轧变形量为90% 的Mg-1.5Zn-0.2Ce合金板材具有更为优异的成形性能。同时也表明,在Mg-1.5Zn中添加0.2%的Ce元素后,IE值由2.60增加至5.46。     

Microstructure characteristics and liquation behavior of fiber laser welded joints of Mg-5Zn-1Mn-0.6Sn alloy sheets

Fine-grained Mg-5Zn-1Mn-0.6Sn alloy sheets of 2 mm in thickness were welded by fiber laser welding. The appearance and microstructures of the welding joints and liquation behaviors in the partially melted zone (PMZ) were investigated. The results show that, with the lower welding power and higher welding speed, the width and depth of the joints decrease. Moreover, some pores are detected at a very high welding speed. There are two kinds of liquation phenomena in the PMZ. One is the liquation network along grain boundaries associated with the liquation of substrate and segregation-induced liquation, the other is the molten pool involved with the liquation of the residual second phases at the boundaries. However, the liquation of substrate and the segregation-induced liquation are the main liquation mechanism in the PMZ.     

Microstructure evolution of casting Mg alloy AM60B subjected to compression deformation

In order to research the microstructure evolution of casting Mg alloy AM60B after compression,the isothermally compressive deformation of different compression ratios followed by metallographic observation was performed.The influence of grain boundaries and second phases on the deformation and recrystallization behavior of the alloy was investigated with optical microscopy,followed by transmission electron microscopy(TEM) to gain an insight into the interplay between the dislocations and microstructure f...     

Mg-5Sn-1Zn-0.5Zr合金的显微组织与时效硬化行为

研究了Mg-5Sn-1Zn-0.5Zr(SZK510)合金经固溶处理(480 ℃×10 h)和175、200、225 ℃,1～100 h时效处理后的时效硬化行为和显微组织特征,并推导出该合金的时效动力学方程.结果表明,固溶时效处理后显微组织由α-Mg和Mg_2Sn,以及少量的MgZn相和α-Zr组成;试验合金具有明显的时效硬化特征:在3个不同的时效温度下,硬化曲线都呈抛物线形状,但在175 ℃时效时,曲线出现两个峰值,并且在保温时间为3.98 h有最大的显微硬度值;试验合金的时效动力学方程符合f=1-exp(-kt~m)关系,随着时效温度提高,k值减小m值增大.     

喷射成形Mg-9Al-xZn合金的微观组织演变

利用喷射成形技术制备AZ91、AZ92和AZ93镁合金沉积柱坯,并对其微观组织演变进行观察.结果表明:铸态普通凝固AZ91合金的晶粒粗大,脆性β-Mg17Al12相连续分布成网状结构;而喷射成形AZ91、AZ92和AZ93合金的组织均匀,晶粒被充分细化,β-Mg17Al12相的网状结构被打破;喷射沉积快速凝固条件下高的冷却速率促进了过饱和α-Mg固溶体组织的形成,使得偏析相减少,形态改善;Zn含量的增加降低了Al在Mg中的溶解极限,促进了β-Mg17Al12相在晶界的析出及α-Mg+β-Mg17Al12离异共晶组织的形成;Zn元素的偏析倾向为激活成分过冷区内的形核质点提供了驱动力,从而阻碍了晶粒长大.     

Effect of high pressure on microstructure of cast Mg-8Zn-0.5Zr-0.5Gd alloy

Mg-8Zn-0.5Zr-0.5Gd alloy was prepared by high pressure solidification. Effect of high pressure on microstructure, micro-hardness and corrosion behavior in Hank's solution of the Mg-8Zn-0.5Zr-0.5Gd alloy were investigated by means of optical microscopy(OM), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), and X-ray diffractometer(XRD). The results showed that, compared with the conventional solidification, high pressure solidification obviously refined the grain size of Mg-8Zn-0.5Zr-0.5Gd alloy. The grain size was refined from 200-300 μm to 100-200 μm and the secondary dendrite arm spacing reduced from 30-50 μm to 10-30 μm. Moreover, the solubility of Zn in the alloy increased and the amount and size of Mg-Zn-Gd phases significantly decreased. The micro-hardness of the alloy solidified under high pressure was improved significantly from 56.17 HV to 63.14 HV. The polarization resistance(Rp) of the alloy had a substantial increase in simulated body fl uid, thus the corrosion rate was significantly reduced from 4.0 to 2.7 mm·year-1.