Mg-9Gd-4Y-2Zn-0.5Zr合金连续降温压缩扭转组织演变

采用Gleeble-3500热力拟试验机对Mg-9Gd-4Y-2Zn-0.5Zr合金棒材进行了热压缩扭转实验,变形过程中采用连续降温,温度范围为420~480℃,降温速率为10℃·s^(-1)。分析了变形后试样微观组织的演化规律。结果表明,形成了梯度组织;随棒状试样半径的增加,晶粒尺寸、LPSO相尺寸及ED//<0001>织构强度均减小。晶内LPSO相发生了机械破碎和扭折;块状LPSO相发生溶解,形成条纹状结构,部分条纹状结构在外力条件下发生扭折。变形过程中主要发生了连续动态再结晶及LPSO相激发的再结晶。连续降温有利于再结晶形核,产生大量细小的动态再结晶晶粒,抑制了再结晶晶粒长大和ED//<0001>织构强度增加。

第二相体积分数对Mg-13Gd-4Y-2Zn-0.5Zr合金力学性能的影响

采用万能拉伸试验机、SEM、EDS及XRD对固溶处理后的Mg-13Gd-4Y-2Zn-0.5Zr合金力学性能、第二相形态、化学成分进行了分析,并利用Image-Pro-Plus软件对第二相体积分数进行了统计。结果表明:固溶处理后,合金中仍有大量不同形态、成分的第二相,主要是灰色块状LPSO相、灰色棒状LPSO相和白色点状富稀土相。随着固溶时间的增加,Mg-13Gd-4Y-2Zn-0.5Zr合金的抗拉强度与伸长率表现出先降低后升高的变化规律。在510℃固溶16 h,合金的抗拉强度与伸长率达到最小值,分别为196.77 MPa、3.8%。510℃固溶10~16 h,LPSO相体积分数不变,富稀土相体积分数增加,富稀土相质地较脆,受力时容易破碎,成为裂纹萌发和扩展的源头,使合金抗拉强度、伸长率均降低。510℃固溶16~19 h,富稀土相体积分数减少,合金的力学性能增加。

Effect of heat treatment on corrosion behaviors of Mg-6Gd-3Y-0.5Zr alloy

The microstructures and corrosion behaviors of as-cast,T4-treated,and T6-treated Mg-6Gd-3Y-0.5Zr alloys were systematically investigated by SEM,TEM,immersion test,and electrochemical corrosion test.The results show that the microstructure of the as-cast alloy is composed ofα-Mg and Mg_(24)(Gd,Y)_(5)eutectic phase,and in T4-treated alloy,Mg_(24)(Gd,Y)_(5)phase dissolves into theα-Mg matrix,leading to an increase in the(Y,Gd)H_(2)phase.After T6 treatment,nanoscale Mg_(24)(Gd,Y)_(5)phase dispersedly precipitates from theα-Mg matrix,and exhibits a specific orientation relationship with theα-Mg:(332)Mg_((24)(Gd,Y)_(5))//(1011)_(α-Mg),[136]Mg_((24)(Gd,Y)_(5))//[1210]_(α-Mg).The corrosion resistance of the Mg-6Gd-3Y-0.5Zr alloys can be ranked in the following order:T6-treated alloy exhibits the highest corrosion resistance,followed by the T4-treated alloy,and finally,the as-cast alloy.The corrosion products of the alloys are all composed of MgO,Mg(OH)_(2),Gd_(2)O_(3),Y_(2)O_(3),and MgCl_(2).The corrosion behavior of Mg-6Gd-3Y-0.5Zr alloy is closely related to the precipitated phase.By establishing the relationship between corrosion rate,hydrogen evolution rate,and corrosion potential,it is further demonstrated that during the micro galvanic corrosion process,the coarse Mg_(24)(Gd,Y)_(5)phase in the as-cast alloy undergoes extensive dissolution,and(Y,Gd)H_(2)phase promotes the dissolution of theα-Mg matrix in the T4-treated alloy,intensifying the hydrogen evolution reaction.The T6-treated alloy,with dispersive precipitation of nanoscale Mg_(24)(Gd,Y)_(5)phase,exhibits better corrosion resistance performance.

均匀化退火处理对Mg-10Gd-4Y-1Zn-0.5Zr合金微观组织的影响

均匀化退火处理对Mg-Gd-Y-Zn-Zr合金的微观组织具有重要影响,特别是LPSO结构的演变对于稀土镁合金的推广应用具有重要的作用。为研究均匀化退火处理对Mg-Gd-Y-Zn-Zr合金组织演变的影响,采用氩气保护真空电阻炉熔铸Mg-10Gd-4Y-1Zn-0.5Zr(质量分数,%)铸棒,随后进行均匀化退火处理,并采用光学、扫描电子及透射电子显微镜对铸态和均匀化退火态试样进行显微组织分析。结果显示,铸造态试样由少量随机散布的孤岛状Mg5.05(Gd,Y,Zn)微粒相、粗大块状Mg10(Gd,Y)Zn共晶相、少量Mg-RE微粒相及大量粗壮基体α-Mg组成,平均晶粒尺寸为91.2μm;均匀化退火态合金由基体α-Mg和Mg12(Gd,Y)Zn及Mg-RE等第二相组成,平均晶粒尺寸为142.1μm。相较铸态,均匀化退火态晶粒发生显著生长,晶界处粗大的块状Mg5(Gd,Y,Zn)共晶相和18R-LPSO结构转变为晶粒内部细小层片状14H-LPSO结构,基体中的LPSO结构数量增多,形貌由粗大块状演变为密集细小的层片状,且未有高密度位错和第二相,表明均匀化退火过程有效促进了合金的软化,对后续塑性加工的进行有重要作用。

挤压比对Mg-9Gd-4Y-2Zn-0.5Zr合金组织和力学性能影响

对Mg-9Gd-4Y-2Zn-0.5Zr合金进行了不同挤压比的挤压试验,采用光学显微镜(OM)、扫描电子显微镜(SEM)、拉伸试验研究了不同挤压比对合金组织与力学性能的影响。结果表明:均匀化态试验合金组织主要由α-Mg基体、层状LPSO相及少量块状LPSO相构成。随着挤压比的增加,合金再结晶程度越来越高,层状LPSO相逐渐减少。与均匀化态试验合金相比,挤压态合金的强度及伸长率均有明显提高。随着挤压比的增加,试验合金的强度有小幅提升,伸长率显著提高。挤压比为42的Mg-9Gd-4Y-2Zn-0.5Z合金的抗拉强度、屈服强度及伸长率均达到最大值,分别为407、332MPa和12.2%。

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 ageing time on corrosion behavior of Mg-10Gd-4.8Y-0.6Zr extruded-alloy

The corrosion behaviors of Mg-10Gd-4.8Y-0.6Zr extruded-alloys with various ageing time were investigated by immersion test and electrochemical measurements.The results show that the corrosion rate of the experimental alloy decreases with the increase of ageing time from 0 to 108 h.The corrosion resistance of the experimental alloy was found to increase with the increase of the size of the precipitate phases.The open circuit potential of the experimental alloy increases with the increase of the ageing time.The potentiodynamic polarization curves show that the cathodic over-potential increases with the increase of ageing time,leading to a decrease in the current density of anodic current plateau with the increase of ageing time.

挤压态Mg-Gd-Y-Zn-Zr合金摩擦磨损行为研究

镁合金是目前工程应用中最轻的结构金属,广泛应用于航空航天与国防军工等制造领域,铸造镁合金由于性能劣势难以应用于重要结构件,塑性变形可以显著细化镁合金晶粒,提高合金综合力学性能。研究发现通过变形调控合金第二相体积分数/尺寸/分布规律、再结晶比例以及晶粒尺寸,可以在提高合金拉伸性能的同时提升合金的耐磨性,这为拓宽镁合金的应用提供了新途径。实验研究了Mg-9Gd-4Y-2Zn-0.5Zr合金经过正挤压-双向转角挤压后的不同位置组织演变特征,并分析了变形合金在不同载荷(10、20、30 N)下的摩擦磨损行为,结果表明:随着载荷增大,变形合金的平均摩擦系数降低;施加载荷相同时,合金的平均摩擦系数值与再结晶程度成正比,磨损量随再结晶比率增大而减少;在摩擦磨损实验中,所有样品均发生氧化磨损和磨料磨损,低载荷下发生轻微的划痕和磨损痕迹,随着载荷增加,出现明显的表面剥落和脱落现象;实验中由于载荷和摩擦力的作用,长周期堆垛有序相(LPSO)颗粒与镁基体间发生相对滑动或剪切,这种相互作用导致LPSO相颗粒剥离和表面颗粒脱落。

Low temperature mechanical properties of as-extruded Mg-10Gd-3Y-0.5Zr magnesium alloy

Influence of multi-cycle cryogenic treatment and tensile temperature on microstructure, mechanical properties and fracture mechanism of as-extruded Mg-10Gd-3Y-0.5Zr magnesium alloy was investigated. The results show that there have no significant changes in tensile properties of the tested alloy after 10 d in liquid nitrogen immersion or 10 cycles of high-low temperature treatment at all test temperatures. The room temperature ultimate tensile strength increases from 398 MPa to 417 MPa after 20 cycles of high-low temperature treatments. Compared with the room temperature, the tested alloys exhibit higher tensile properties at low temperatures. At -196 °C, the yield strength and ultimate tensile strength of the as-extruded-T5 Mg-10Gd-3Y-0.5Zr alloy are 349 MPa and 506 MPa, respectively, increasing by about 18% and 27%, respectively. The transgranular cleavage fracture mechanism is observed at room temperature, while at low temperatures both ductile fracture and cleavage fracture behaviors coexist.

Mg-10Gd-4.8Y-0.6Zr镁合金热变形行为与加工图

在Gleeble-1500热/力模拟机上,对Mg-10Gd-4.8Y-0.6Zr镁合金进行高温压缩试验,压缩时设定应变速率范围为0.001～1 s-1,温度范围为623～773 K,最大真应变为1.3;研究该合金高温变形时流变应力与应变速率、变形温度之间的关系及变形过程中的微观组织演化;计算塑性变形表观激活能及相应的应力指数;建立该合金的加工图。结果表明:在该合金的加工图中,功率耗散系数η随应变速率的降低及温度的升高而不断增加,失稳区域随应变量的增加而扩大;综合得出该合金的最佳实际变形工艺为温度723～773 K、应变速率0.1～1 s-1。

Microstructure and mechanical property of a high-strength Mg-10Gd-6Y-1.5Zn-0.5Zr alloy prepared by multi-pass equal channel angular pressing

In this work,a high-strength Mg–10Gd–6Y–1.5Zn–0.5Zr(wt.%)alloy was fabricated by successive multi-pass equal channel angular pressing(ECAP).The microstructure and mechanical property of as-cast and ECAP alloys were systematically researched by X-ray diffractometer,scanning electron microscopy,transmission electron microscopy and compression test.The results show that the microstructure of as-cast alloy consists ofα-Mg grains,Mg24Y5 networks,18R blocks,fine 14H lamellas,and fewY-rich particles.After 8 passes ECAP,dynamic recrystallization ofα-Mg is developed and their average grain size decreases to about 1μm.The network Mg_(24)Y_(5) phase at grain boundaries is broken into small particles with average diameter lower than 0.5μm.Moreover,18R blocks are kinked and delaminated,or broken into small particles and blended with Mg24Y5 particles.14H lamellas grow gradually or are dynamically precipitated within certainα-Mg grains.Compression tests indicate that 8p ECAP alloy exhibits excellent mechanical property with compressive strength of 537 MPa and fracture strain of 17.0%.The significant improvement for both strength and ductility of deformed alloy could be ascribed to DRX grains,refined Mg24Y5 particles,18R kinking and dynamical precipitation of 14H.

Microstructure evolution of semi-solid Mg-10Gd-3Y-0.5Zr alloy during isothermal heat treatment

In this study,the microstructure evolution of semi-solid Mg-10Gd-3Y-0.5Zr alloy during isothermal heat treatment has been investigated.The results show that primary particles coarsen continuously during the holding.Coarsening rate decreases with the increase of isothermal temperature.When isothermal temperature increases from 600℃ to 620℃,the dominant mechanism for coarsening changes from particle coalescence to Ostwald ripening.Equiaxed as-cast microstructure is beneficial to the semi-solid microstructure after isothermal heat treatment,which brings about the refinement and spheroidization of primary particles,and shortening of holding time.Significant modification of second phases can also be achieved after isothermal heat treatment,due to its unique solidification process.The optimum processing parameters for Mg-10Gd-3Y-0.5Zr alloy in isothermal heat treatment are isothermal temperature of 610℃-620℃ and holding time of 20-40 min.

Effect of heat treatment on microstructures and mechanical properties of sand-cast Mg-4Y-2Nd-1Gd-0.4Zr magnesium alloy

Influence of heat treatment on the microstructures and mechanical properties of sand-cast Mg-4Y-2Nd-1Gd-0.4Zr magnesium alloy was investigated,and the tensile fracture mechanisms of the studied alloys under different conditions were also discussed.The results show that the optimum T4 and T6 heat treatment conditions for the as-cast Mg-4Y-2Nd-1Gd-0.4Zr alloy are 525°C,8 h and（525°C,8 h）＋（225°C,16 h）,respectively,with regard to the microstructure observation,DSC heating curve and mechanical properties.The hardness,yield strength,ultimate tensile strength and elongation of the Mg-4Y-2Nd-1Gd-0.4Zr alloy treated by optimum T6 heat treatment are HV91,180 MPa,297 MPa and 7.4%,respectively.Moreover,the Mg-4Y-2Nd-1Gd-0.4Zr alloys under different heat treatment conditions exhibit different tensile fracture modes.

Mg-12Gd-4Y-1Zn-0.5Zr合金的显微组织和力学性能

研究了铸态、热挤压态和热挤压加时效处理的Mg-12Gd-4Y-1Zn-0.5Zr合金的显微组织特征和室温拉伸性能.结合SEM-EDS和TEM-EDS重点分析了热挤压态的合金的相组成.结果表明:合金的铸态组织主要由αVMg基体和沿晶界分布的片层状的第二相组成,经过370℃热挤压变形后,合金中第二相的分布和形貌均发生变化,200℃,70 h时效处理后第二相分布变得不规则.并发现了两种非平衡相,即片状的Mg(GdZn)5和块状的Mg3(Gd0.5Y0.5)相.热挤压变形加时效处理后合金室温抗拉强度显著提高的同时,且具有良好的延伸率.

Comparative study on corrosion behavior of as-cast and extruded Mg-5Y-7Gd-1Nd-0.5Zr alloy in 5% NaCl aqueous solution

The corrosion behaviours of Mg-5Y-7Gd-1Nd-0.5Zr magnesium alloys prepared by as-casting and extrusion were investigated in 5% NaCl aqueous solution by immersion and electrochemical tests. The microstructure indicates the mean grain size of 15 μm for the extruded and 100 μm for the as-cast Mg-5Y-7Gd-1Nd-0.5Zr magnesium alloys. The corrosion morphology of as-cast sample shows pitting corrosion and little filiform corrosion, but that of the extruded sample shows pitting corrosion at the initial stage. The corrosion rate of extruded sample is higher than that of as-cast Mg-5Y-7Gd-1Nd-0.5Zr alloy according to the immersion test. The second phases containing RE acting as cathodes improve the corrosion properties. The corrosion potentials of as-cast and extruded Mg-5Y-7Gd-1Nd-0.5Zr alloys are -1.658 V and -1.591 V, respectively. The origins of the distinctive corrosion behavior of as-cast and extruded Mg-5Y-7Gd-1Nd-0.5Zr Mg alloys were discussed.

Effect of heat treatment on corrosion behavior of low pressure sand cast Mg-10Gd-3Y-0.5Zr alloys

The corrosion behaviors of low-pressure sand cast Mg-10Gd-3Y-0.5Zr(wt.%)alloys in as-cast,solution treated(T4)and aged(T6)conditions were studied by means of immersion test and electrochemical measurements in 5wt.%NaCl solution saturated with Mg(OH)_(2).It was observed that the corrosion rate in the T4 condition was lower than that of the as-cast and T6 conditions by both sand casting and permanent mold casting with the same order of as-cast>T6>T4;while the corrosion resistance of the permanent mold casting is superior to the sand casting.The morphologies of the corrosion products are similar porous structures consisting of tiny erect flakes perpendicular to the corroded surface of the alloy,irrespective of the heat treatment conditions.Especially,the corrosion film in T4 condition is more compact than that in the other two conditions.In addition,the severer corrosion happening to the as-cast condition is correlated with the galvanic corrosion between the matrix and the eutectic compounds;while improved corrosion resistance for the T4 and T6 conditions is ascribed to the dissolution of the secondary eutectic compounds.The measured corrosion current densities of Mg-10Gd-3Y-0.5Zr alloys in as-cast,T4,and T6 conditions are 36μA·cm^(-2),10μA·cm^(-2),and 33μA·cm^(-2),respectively.The proposed equivalent circuit[Rs(CPE_(1)R_(t)R_(f)CPE_(2))]by Zview software matches well with the tested electrochemical impedance spectra(EIS)data.

成形温度对Mg-13Gd-4Y-2Zn-0.5Zr合金旋转反挤压变形组织和性能的影响

为达到晶粒细化和提高力学性能的目的,采用旋转反挤压变形工艺对高强耐热Mg-13Gd-4Y-2Zn-0. 5Zr合金进行剧烈塑性变形。利用Gleeble-3500热模拟试验机研究了Mg-13Gd-4Y-2Zn-0. 5Zr合金杯形件成形过程中成形温度对材料组织和性能的影响规律。结果表明:在变形过程中,合金基面滑移困难,产生了不连续的动态再结晶,随温度的升高,再结晶晶粒长大,在长大的再结晶晶界与原始晶界处产生二次再结晶。变形区域内的晶粒为随机取向,随温度的变化发生旋转,在450℃下晶粒的基面平行于挤压方向,织构强度弱化。变形区域内各区域硬度值相差不大,在轴心附近的硬度值相对较低,且在450℃下硬度值最低。

铸态Mg-9Gd-4Y-xZn-0.5Zr合金组织和力学性能

采用X射线衍射仪、光学显微镜、扫描电镜、能谱分析仪以及拉伸试验机,研究了Zn对铸态Mg-9Gd-4Y-xZn-0.5Zr（x=0,0.5 1.0,1.5,2.0）合金组织和力学性能的影响。结果表明：铸态Mg-9Gd-4Y-0.5Zr合金显微组织由基体α-Mg和共晶相Mg5（Gd,Y）组成。加入Zn元素后,合金组织中出现Mg5（Gd,Y,Zn）相和Mg12Zn（Gd,Y）相,分布于晶界或晶内。当Zn含量为1%时,合金组织得到明显细化,第二相分布均匀,力学性能显著提升。此时,合金抗拉强度和屈服强度到达最大值,分别为209.72 MPa和172.69 MPa。随着Zn含量进一步增加,合金组织粗化,第二相含量迅速增加且沿晶界逐渐呈网状分布并逐渐向晶内深入,合金强度也明显降低。

Mg-9Gd-4Y-1Zn-0.5Zr合金的高温蠕变行为

采用光学显微镜和蠕变实验机研究Mg-9Gd-4Y-1Zn-0.5Zr合金在不同温度和应力下的高温蠕变行为。结果表明：在应力为70～130 MPa范围内,200℃时Mg-9Gd-4Y-1Zn-0.5Zr合金的蠕变应力指数n=1.63,蠕变机制为晶界滑动,250℃时蠕变应力指数n=2.63,蠕变机制为位错滑移;在蠕变温度为200～250℃范围内,应力分别为70、90、110和130 MPa时,合金的蠕变激活能Qc分别为108.5、118.9、127.6和134.3 k J/mol;随着温度和应力的增加,合金晶粒长大,合金的蠕变机制由晶界滑动控制转变为位错滑移控制。

Mg-13Gd-4Y-2Zn-0.5Zr镁合金减振性能的研究

采用TA Q800 DMA对Mg-13Gd-4Y-2Zn-0.5Zr镁合金进行阻尼性能测试,并通过阻尼-应变、应力-应变曲线的拟合公式计算出减振系数。结果表明：不同热处理工艺对合金的减振性能有一定的影响。热变形、热处理对合金内的析出相有调控作用,进而影响合金的阻尼性能。高应变区域,变形＋T6态合金内的析出相最小,数量最多,其阻尼性能最差。合金的屈服强度对减振系数有较大影响,变形＋T6态合金的减振系数较高,变形态次之,铸态合金的最小。