Microstructure and mechanical properties of Mg-4.0Zn-0.5Ca alloy

A new kind of Mg-4.0 wt.%Zn-0.5 wt.%Ca alloy is fabricated by casting and hot extrusion for used as a high performance structure material as well as a biomaterial. In the as-cast alloy, the average grain size of the α-Mg is 120-150 µm and the precipitated second phases are distributed uniformly in α-Mg grains. The as-cast Mg-4.0 wt.%Zn-0.5 wt.%Ca alloy shows a good balance between the tensile strength (211 MPa) and ductility (17% in elongation). After hot extrusion at 593 K, the second phase is greatly refined and the average grain size of the α-Mg is reduced to 8-12 μm which is resulted from dynamic re-crystallization during hot extrusion. In this case, it exhibits a high tensile strength (273 MPa) and a high ductility (34% in elongation) at room temperature.     

RE对Mg-8Zn-4Al-0.3Mn镁合金阻尼性能的影响

研究了 RE对Mg-8Zn-4Al-0.3Mn镁合金阻尼性能的影响.研究表明,加入RE后降低了合金低温下的阻尼性能,但明显提高了其在高温下(≥120℃)的阻尼性能.高温下,加入1.0%RE的合金表现出了最高的阻尼性能.由于高温下合金中相界面的软化及粘性滑动,四种合金在高温下均存在一个温度内耗峰,只是出现的温度不同.RE的加入推迟了温度内耗峰出现的温度.分析认为,加入RE后合金的阻尼机制主要是位错机制和界面机制.可动位错密度越高,晶粒越细,晶界和相界越多,阻尼性能越好.     

铸造Mg-3Zn-0.5Cu-0.6Zr镁合金的时效析出行为研究

利用金相显微镜、显微硬度计、X射线衍射仪、扫描和透射电镜研究了铸造Mg-3Zn-0.5Cu-0.6Zr镁合金铸态和固溶时效后的显微组织,初步确定了时效Mg-3Zn-0.5Cu-0.6Zr镁合金中主要合金相的种类和形态.合金铸态组织主要由初晶Mg基体和(Mg+Mg2Cu,CuMgZn)共晶组成.固溶后,晶界处大部分非平衡共晶组织溶解;180℃/20h时效后达到合金时效硬度峰值,此时晶内析出相主要有三类:(1)轴线垂直于(0001)Mg,板条状或棱柱状β2’-MgZn2,长度50nm～200nm,该相是合金的主要时效硬化相;(2)较粗大的、其轴线仍与基面垂直的六棱柱状β2’-MgZn2;(3)轴线平行于(0001)Mg,板条状或针状β-MgZn,长度50nm～150nm.     

Heat-treatable Mg-9Al-6Sn-3Zn extrusion alloy

Mg-9Al-6Sn-3Zn (wt%) alloy was extruded and heat treated in T5 and T6 conditions, and its mechanical properties and microstructures were investigated. The extruded product can be slightly strengthened by the T5 treatment as a result of sparse and heterogeneous precipitation. Significant increase in strength is achieved by the T6 treatment, and this is mostly attributed to the formation of lamellar discontinuous Mg₁₇Al₁₂ precipitates. The segregation of Al and Zn at grain boundaries is responsible for the discontinuous Mg₁₇Al₁₂ nucleation. The T6-treated alloy exhibits a tensile yield strength of 341 MPa and an ultimate tensile strength of 409 MPa, together with an elongation to fracture of 4%.     

Effects of samarium on microstructures and tensile properties of Mg-5Al-0.3Mn alloy

Microstructures and tensile properties of Mg-5Al-0.3Mn-xSm (x = 0, 1, 2 and 3 wt.%) alloys prepared by metal mould casting method were investigated. It was demonstrated that Mg-5Al-0.3Mn alloy was mainly composed of α-Mg and β-Mg₁₇Al₁₂ phases. However, the other two precipitates (Al₁₁Sm₃ and Al₂Sm) were observed along grain boundaries in the alloys containing Sm. The amount of Al₁₁Sm₃ and Al₂Sm precipitates was increased with the increment of Sm content. Meanwhile, volume fraction of β-Mg₁₇Al₁₂ phase was decreased. Moreover, the morphology of β-Mg₁₇Al₁₂ was altered from bulk bone-like shape to spherical one. Tensile results showed that Mg-5Al-0.3Mn-2Sm alloy exhibited the highest tensile properties both at room temperature and 150 °C. Compared with ultimate tensile strength (UTS), yield strength (YS) and elongation (?) of Mg-5Al-0.3Mn alloy, UTS, YS and ? of Mg-5Al-0.3Mn-2Sm alloy were enhanced by 30%, 45% and 35% at room temperature, and by 17%, 48% and 96% at 150 °C, respectively. The improvement of tensile properties was attributed to the decreased amount of β-Mg₁₇Al₁₂ and its refined morphology, and high thermal stable Al₁₁Sm₃ and Al₂Sm precipitates which effectively prohibited dislocation movement and grain boundary sliding during deformation process.     

双级时效对Al-7.02Zn-2.6Mg-0.35Mn合金组织及性能的影响

以真空熔炼制备的Al-7.02Zn-2.6Mg-0.35Mn合金为研究对象,进行均匀化、固溶处理和双级时效处理.测试合金硬度,观察合金组织,研究合金腐蚀性能.结果表明,在终时效160℃×8 h下,Al-7.02Zn-2.6Mg-0.35Mn合金时效硬化曲线呈现出两个硬度峰值,在预时效4 h观察到第一个硬度峰值(峰值Ⅰ)...     

Microstructure and mechanical properties of as-cast Mg-4Zn-0.5Zr-0.2Cu-0.2Ce alloy

In this study, an approach is proposed to improve the microstructure and mechanical properties of Mg-4Zn-0.5Zr alloy by combining trace Cu and rare earth Ce addition. The results showed that Cu and Ce additions led to obvious grain refinement and the formation of Mg-Zn-Cu and Mg-Zn-Ce phases. The Mg-Zn-Ce phase was identified to have an orthorhombic structure. The length of the [0001]_α rods in the Cu-containing alloys remarkably decreased. The yield strength increased slightly after Cu and Ce co-addition, which was attributed to grain refinement and precipitation strengthening. The coarse Mg-Zn-Ce phase distributed at the grain boundaries would reduce the ductility by promoting crack propagation during tensile processes.     

Mg-9Gd-4Y-2Zn-0.5Zr镁合金的微观组织与性能研究

目的 研究挤压比对热挤压制备的Mg-9Gd-4Y-2Zn-0.5Zr(VW94)镁合金微观组织、拉伸性能和抗腐蚀性的影响,并揭示挤压比对组织和性能演变的影响机制。方法 用挤压比为16和35的热挤压工艺制备了Mg-9Gd-4Y-2Zn-0.5Zr(VW94)镁合金,通过光镜（OM）、X射线衍射仪（XRD）、扫描电子显微镜（SEM）等手段表征并分析了不同挤压比下的微观组织,进一步通过拉伸测试和电化学测试评估合金的力学性能和腐蚀速率,并通过SEM表征断口形貌和腐蚀形貌,分析其断裂方式和腐蚀机制。结果 挤压比的大小并不会影响镁合金的相成分,镁合金主要由α-Mg基体及晶界处的LPSO相组成。当挤压比为16时,第二相数量更多,平均晶粒尺寸更小;当挤压比增大到35时,合金的再结晶程度更高,其晶粒尺寸分布更加均匀。性能表征结果发现,挤压比为16的VW94合金的力学性能更优,其抗拉强度及伸长率分别达到376.3MPa和13.3%,但是挤压比为35的VW94合金的耐腐蚀性能更好。结论 挤压比虽然不会影响相的种类,但是会影响第二相的含量和晶粒尺寸,从而进一步影响拉伸性能和腐蚀速率,因此可以通过优化挤压比协同...     

Sb对Mg-3Sn-1.5Al-1Zn-1.2Si合金组织性能的影响

在熔炼过程中以单质形式加入Sb,研究了0~1.8%(质量分数,下同)范围内不同含量的Sb对Mg-3Sn-1.5Al-1Zn-1.2Si合金显微组织和力学性能的影响。结果表明,Sb能与Mg基体优先生成Mg3Sb2相,加入1.0%的Sb对Mg2Si相的汉字状结构变质作用显著,Mg2Si中的Si能与Sn发生取代反应,生成富Sn的Mg2(Si,Sn)。随着Sb的增加,铸态合金和挤压态合金的延伸率逐渐减小,而抗拉强度呈现先增加后降低的趋势,塑性和强度的最佳配合点约为1.0%,Sb含量的增加有利于改善Mg-3Sn-1.5Al-1Zn-1.2Si合金的耐热性能。     

热处理对SCR成形Al-1.5Mg-0.3Sc合金线材性能的影响

采用单辊搅拌冷却技术（Shearing—Cooling-Rolling，简称SCR）和在线固溶处理方法制备了Al-1．5Mg-0．3Sc（wt％）合金线材，研究了不同在线固溶温度条件下时效处理对合金线材的微观组织和拉伸性能的影响．结果表明：SCR技术对合金线材具有剪切细化功能，在铝基体内产生大量位错，时效析出大量Al3Sc强化相粒子，与位错交互作用．随着在线固溶温度下降，合金线材时效析出沉淀相Al3Sc的弥散度增加，合金线材的抗拉强度和延伸率提高；随着过时效时间的延长，合金线材的抗拉强度下降，线材的延伸率提高，时效8h，延伸率达峰值．     

时效Mg-8.14Zn-1.44Y-0.5Zr合金高温摩擦磨损性能研究

镁合金在航空航天、汽车及通讯领域有着广泛的应用, 为进一步改善镁合金的耐磨性,在不同温度下对Mg-8.14Zn-1.44Y-0.5Zr合金进行了时效处理,并测试了铸态和时效态合金的硬度及高温条件下摩擦磨损行为.采用扫描电子显微镜对不同载荷及环境温度条件下合金的摩擦磨损表面进行观察,并分析了其磨损机制.结果表明：在240 ℃时,随着时效时间的增加,合金的硬度值呈现先增加而后降低的趋势,当时效温度为240 ℃,时间为12 h时,Mg-8.14Zn-1.44Y-0.5Zr合金具有最高的硬度值; 铸态合金的磨损体积损失明显高于时效态合金,两种合金的磨损体积损失均随载荷和环境温度增加而增大,且时效态合金发生严重磨损时对应的转变温度滞后于铸态合金; 环境温度低于250 ℃时,合金的磨损机制主要为磨粒磨损和氧化磨损,环境温度为300 ℃时,磨损机制变为剥层磨损和黏着磨损.时效处理可显著提高Mg-8.14Zn-1.44Y-0.5Zr合金的硬度及耐磨性.     

Mg-4Zn-3Y合金高温阻燃特性

为了改善镁合金在熔铸及加工过程中抗氧化燃烧性能,用合金化阻燃方法在Mg-4Zn合金中添加适宜的Y元素制备了阻燃效果优异的Mg-4Zn-3Y合金.采用俄歇电子能谱仪、X射线衍射仪和扫描电镜(SEM+EDS)研究了氧化膜的显微形貌、合金元素分布及其物相组成.结果表明,Mg-4Zn-3Y合金在高温下暴露于大气中时,燃点提高250℃,合金表面生成一层以Y2O3为主的氧化膜,改善镁合金氧化膜的粘附性,提高高温抗氧化和燃烧能力.基于高温氧化热力学分析,建立了Mg-4Zn-3Y合金在高温下的氧化物理模型.Mg-4Zn-3Y合金能在1065K时于大气中保温30min而不燃烧,实现了低Y元素含量镁合金在大气条件下的无保护熔炼.     

Effect of trace HA on microstructure,mechanical properties and corrosion behavior of Mg-2Zn-0.5Sr alloy

Effect of the addition of trace HA particles into Mg-2Zn-0.5Sr on microstructure, mechanical properties, and bio-corrosion behavior was investigated in comparison with pure Mg. Microstructures of the Mg-2Zn-0.5Sr-xHA composites(x = 0, 0.1 and 0.3 wt%) were characterized by optical microscopy(OM),scanning electron microscopy(SEM) equipped with energy dispersion spectroscopy(EDS) and X-ray diffraction(XRD). Results of tensile tests at room temperature show that yield strength(YS) of Mg-2Zn-0.5Sr/HA composites increases significantly, but the ultimate tensile strength(UTS) and elongation decrease with the addition of HA particles from 0 up to 0.3 wt%. Bio-corrosion behavior was investigated by immersion tests and electrochemical tests. Electrochemical tests show that corrosion potential(Ecorr)of Mg-2Zn-0.5Sr/HA composites significantly shifts toward nobler direction from-1724 to-1660 m VSCE and the corrosion current density decreases from 479.8 to 280.8 μA cm~(-2) with the addition of HA particles. Immersion tests show that average corrosion rate of Mg-2Zn-0.5Sr/HA composites decreases from11.7 to 9.1 mm/year with the addition of HA particles from 0 wt% up to 0.3 wt%. Both microstructure and mechanical properties can be attributed to grain refinement and mechanical bonding of HA particles with second phases and α-Mg matrix. Bio-corrosion behavior can be attributed to grain refinement and the formation of a stable and dense CaHPO_4 protective film due to the adsorption of Ca~(2+)on HA particles. Our analysis shows that the Mg-2Zn-0.5Sr/0.3HA with good strength and corrosion resistance can be a good material candidate for biomedical applications.     

室温强塑性变形下回溶和再析出的机理研究

为了研究室温强塑性变形下回溶和再析出的机理,利用透射电镜、硬度测量等手段,采用压缩变形方法对Al-Zn-Mg-Cu铝合金在强塑性变形下第二相的回溶和再时效过程进行了观察.研究结果表明:强塑性变形过程中存在第二相回溶和再析出的交替过程;由强变形产生的过饱和固溶体再时效时,在高密度的缠结位错区或者等轴超细晶粒的边界上直接析出平衡相η.     

Ca对Mg-8Zn-3.2Al-0.9Si-0.3Mn合金显微组织及性能的影响

采用光学显微镜(OM)、X射线衍射仪(XRD)、带能谱分析(EDS)的扫描电子显微镜(SEM)等分析手段研究了元素Ca对Mg-8Zn-3.2Al-0.9Si-0.3Mn合金基体及Mg2Si相的细化效果及其细化机制。结果表明:Ca的加入能够使Mg2Si初生相由粗大的汉字状变为细小、弥散分布的颗粒状,并使合金基体组织显著细化。Ca对Mg2Si相的变质是以CaSi2作为Mg2Si相的异质形核核心和Ca作为表面活性元素影响其生长两种机制共同作用的结果。由于显微组织的改善,使得合金的室温和高温力学性能均得到提高。     

Mg-11Li-3Al-0.5RE合金在碱性NaCl溶液中的腐蚀特性

用静态失重法、动电位极化曲线和电化学交流阻抗谱等方法研究了Mg-11Li-3Al-0.55RE合金在碱性NaCl溶液中的腐蚀行为,结果表明:在碱性NaCl溶液中,随着Cl<'-浓度的升高,合金的平均腐蚀速率增大,腐蚀电流增大,体系中Rsol、Rt、Rf减小,腐蚀严重;当溶液的碱性增强时,合金的点蚀电位正移,表面膜钝化作用增强,Rf提高,同时Rt和Rsol增大,减缓了腐蚀的进行;在合金表面生成的腐蚀产物主要成分为Mg(OH)2、Al2O3和Li2O2;Mg-11Li-3Al-0.5RE合金的腐蚀以点蚀为主,逐渐向基体内部和四周扩大,形成较深的蚀坑.     

Mg-3Al-2Zn-2Y合金的动态力学性能研究

在不同应变率压缩与拉伸下,研究了Mg-3Al-2Zn-2Y合金的力学性能,发现2种条件下合金力学性能变化规律不同。压缩情况下,随应变率增大,极限强度与屈服强度先增大后减小,高应变率下(1300～4800s-1)的流变应力大于中低应变率(0.001～1s-1);在0.001～1450s-1拉伸下,随应变率增大,合金的流变应力呈增大趋势,极限强度、屈服强度增大,破坏应变先减小后增大。压缩情况下合金流变应力的应变率敏感性高于拉伸情况。     

均匀化处理对Mg-13Gd-3.5Y-2Zn-0.5Zr镁合金组织和力学性能的影响

对Mg-13Gd-3.5Y-2Zn-0.5Zr镁合金铸锭进行均匀化处理,温度为505～525℃,时间为4～24h,并采用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)和万能材料试验机等检测手段分析均匀化处理前后合金微观组织和力学性能的变化。结果表明:均匀化处理后,原始组织中网状分布共晶化合物转化成晶界处不连续分布的块状LPSO相,离散分布的方块状富稀土相溶解。力学性能测试显示,铸态镁合金的抗拉强度为172.9MPa,伸长率为1.8%,经过均匀化处理后合金的力学性能得到提高,在515℃/16h均匀化制度下,合金室温抗拉强度为212.3MPa,伸长率为3.1%;在200℃下抗拉强度为237.2MPa,伸长率为9.7%,性能达到最佳。断口扫描显示,铸态合金是以撕裂棱与解理台阶为主的解理脆性断裂,均匀化处理后的合金中出现小而浅的韧窝,但仍然是以解理台阶为主的准解理断裂,塑性提高有限,长程有序相可成为裂纹的萌生源。