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.

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.

Evaluation of dynamic performance and ballistic behavior of Ti-5Al-5Mo-5V-3Cr-1Zr alloy

Terminal ballistic tests using 7.62 mm armor-piercing incendiary （API） projectiles were performed to evaluate the resistance to penetration of Ti-5Al-5Mo-5V-3Cr-IZr （Ti-55531） alloy. The dynamic properties were determined by a split Hopkinson pressure bar （SHPB） test system. Ti-55531 plates were subjected to two kinds of heat treatments, leading to the formation of high-strength and high-toughness plates. The results of SHPB test exhibit that the maximum impact absorbed energy of the high-strength plate at a strain rate of 2200 s^-1 is 270 MJ/m^3; however, the maximum value for the high-toughness plate at a strain rate of 4900 s^-1 is 710 MJ/m^3. The ballistic limit velocities for the high-strength and high-toughness plates with dimensions of 300 mm×300 mm×8 mm are 330 and 390 m/s, respectively. Excellent dynamic properties of Ti-55531 alloy correspond to good resistance to penetration. The microstructure evolution related to various impact velocities are observed to investigate the failure mechanism.

Zr-1锆锭缺陷形成原因

某Zr-1锆锭在进行无损检测时发现内部存在缺陷。采用宏观观察、化学成分分析、金相检验、硬度测试、扫描电镜及能谱分析等方法,对该缺陷的形成原因进行了分析。结果表明:锆锭缺陷的形成原因是熔炼时使用的电极被污染,引入了外来夹杂物,导致铜元素被引入Zr-1锆锭,未熔化的氧化铜颗粒和熔化的铜形成了锆铜合金,在Zr-1锆锭中形成了硬脆相夹杂物。

冷变形时效处理对Cu-1.0Cr-0.1Zr合金性能的影响

采用拉伸力学性能测试、电导率测量、金相和透射电镜技术研究不同冷变形下时效处理对Cu-1.0Cr-0.1Zr合金性能的影响。结果表明:Cu-1.0Cr-0.1Zr合金在950℃×1h固溶处理+70%冷变形+450℃×4h时效后的综合性能最好,其抗拉强度、屈服强度、伸长率和电导率分别达到543.3MPa、522.3MPa、12.68%和82.6%IACS。从合金的显微组织观察分析中可知,在此工艺下合金基体中析出了大量弥散细小的强化相,第二相析出是合金强化的重要原因。

Effect of Trace Sc and Zr on the Mechanical Properties and Microstructure of A1 Alloy 2618

An experimental 2618(Al-Cu-Mg-Fe-Ni) alloy added with trace Sc and Zr was prepared by ingot metallurgy (IM) method. The aging behavior of the alloy was studied by Vickers hardness measurement at 200℃ and 300℃. and the tensile properties of alloy specimens were measured at 20℃, 200℃, 250℃ and 300℃. The microstructure was observed by using optical microscope, SEM and TEM. It was found that the addition of Sc and Zr to 2618 alloy resulted in a primary Al_3(Sc,Zr) phase which could refine the grain because it acts as nuclei of heterogeneous crystallization in the melt during solidification. The secondary Al_3(Sc,Zr) particles were full coherent with matrix and had obvious precipitation hardening effect. They also made the S' phase precipitate more homogeneous. So the strength of alloy increases at both ambient and elevated temperatures without a decrease of ductility. The ductile fracture of alloy occurs by microvoid nucleation, growth and coalescence, so the microvoid coalescence is the dominant fracture mechanism.

Shear localization behavior in hat-shaped specimen of near-αTi−6Al−2Zr−1Mo−1V titanium alloy loaded at high strain rate

The microstructure characteristics in early stage shear localization of near-αTi−6Al−2Zr−1Mo−1V titanium alloy were investigated by split Hopkinson pressure bar(SHPB)tests using hat-shaped specimens.The microstructural evolution and deformation mechanisms of hat-shaped specimens were revealed by electron backscattered diffraction(EBSD)method.It is found that the nucleation and expansion of adiabatic shear band(ASB)are affected by both geometric and structural factors.The increase of dislocation density,structure fragment and temperature rise in the deformation-affected regions provide basic microstructural conditions.In addition to the dislocation slips,the extension twins detected in shear region also play a critical role in microstructural fragmentation due to twin-boundaries effect.Interestingly,the sandwich structure imposes a crucial influence on ASB,which finally becomes a mature wide ASB in the dynamic deformation.However,due to much larger width,the sandwich structure in the middle of shear region is also possible to serve as favorable nucleation sites for crack initiation.

Experiment and modeling of TiB_(2)/TiB boride layer of Ti−6Al−2Zr−1Mo−1V alloy

The influence of the boriding conditions on the boride layers was examined by boriding Ti−6Al−2Zr−1Mo−1V alloy in the temperature range of 920−1120℃.The experimental results show that the boride layers were composed of a continuous thin outer layer of TiB_(2) and a thick inner layer of TiB with whiskers or needle-like morphologies that extended into the substrate.Thick and compact boride layers were obtained when the boriding temperatures were 1000−1080℃,and the treatment time exceeded 8 h.The boride layer depth increased with the boriding temperature and time,and the growth kinetics of the boride layers was characterized by a parabolic curve.The growth kinetics of the boride layers,including both TiB_(2) and TiB layers,were predicted by establishing a diffusion model,which presented satisfactory consistency with the experimental data.As a result,the activation energies of boron in the TiB_(2) and TiB layers were estimated to be 223.1 and 246.9 kJ/mol,respectively.

Characteristics of Faigue Crack Initiation in Ti-5Al-4Sn-2Zr-1Mo-0.7Nd-0.25Si Alloy

The characteristics of fatigue crack initiation in Ti-5AI-4Sn-2Zr1Mo-O.7Nd-O.25Si alloy wereStudied. Two modes Of fatigue crack initiation were found. The Nd-rich phase particles displaybetter resistance to fatigue crack initiation than the matrix at lower stress.

复合Zr盐对Mg-1%Y合金凝固组织的影响

研究了复合Zr盐添加温度及保温时间对Mg-1%Y合金凝固组织的影响。结果表明:760℃添加0.31%Zr保温20 min后实验合金的细化效果最好,其平均晶粒尺寸可由原来的4100μm降至105μm。研究还表明:Zr盐的加入也在镁熔体中引入了一些Zr的氧化物,这是降低Zr收得率的原因,同时也增加了熔体净化的难度。

变形热处理对Zr1．0Nb合金耐腐蚀性能的影响

为了探究显微组织对Zr-1.0Nb合金耐腐蚀性能的影响,将Zr-1.0Nb合金样品分别进行680℃/500℃、680℃/560℃、800℃/500℃、800℃/560℃和1000℃/560℃五种变形热处理,然后在350℃、16.8 MPa、0.01mol.L-1的L iOH水溶液中腐蚀,并用透射电镜(TEM)研究其显微组织.其中800℃-1 h/冷轧/500℃-30 h处理样品的耐腐蚀性能最好,基体αZr中Nb元素固溶含量最低.通过变形热处理降低基体αZr中Nb元素固溶含量是提高Zr-1.0Nb合金耐腐蚀性能的一个关键因素.

(Ti_(0.7)Zr_(0.2)V_(0.1))Ni贮氢合金的电化学性能及氢致相变研究

研究了（Ｔｉ０．７Ｚｒ０．２Ｖ０．１）Ｎｉ合金的相结构和电化学性能。结果表明：在比较快的冷却条件下（真空电弧炉熔化，水冷铜坩埚凝固），合金铸态组织为具有Ｂ２结构（ＣｓＣｌ型）的单一奥氏体相；充氢使Ｂ２结构的奥氏体相转变为单斜结构的马氏体相；反复电化学充放氢使Ｔｉ２Ｎｉ和Ｚｒ９Ｎｉ１１相逐渐从母相中析出。在５０ｍＡ／ｇ放电倍率下，（Ｔｉ０．７Ｚｒ０．２Ｖ０．１）Ｎｉ合金的电化学容量可达３８０ｍＡｈ／ｇ，是ＴｉＮｉ二元合金的两倍。但经１０次充放电循环后合金容量迅速衰退至２００ｍＡｈ／ｇ。研究表明，（Ｔｉ０．７Ｚｒ０．２Ｖ０．１）Ｎｉ合金具有较高电化学容量主要是由于在ＴｉＮｉ相的催化作用下，具有高贮氢量的Ｔｉ２Ｎｉ相和Ｚｒ９Ｎｉ１１相能可逆地吸放氢所致，而其较快的容量衰退则主要与Ｔｉ２Ｎｉ相的氧化有关。

核级Zr-1Nb铸锭中Nb元素均匀性控制

针对Zr-1Nb铸锭中Nb元素含量范围窄（0．9％～1．1％），对成分均匀性要求高，且易形成Nb高密度夹杂（HDI）等技术难题，研究了铌元素的添加方式以及真空自耗电弧熔炼工艺参数对Nb成分均匀性的影响。结果表明，以ZrNb中间合金为配料，采用合理的熔炼工艺，可获得无偏析、无HDI冶金缺陷、成分均匀性优良的合金铸锭。

稀土La对Cu-1Cr-0.1Zr合金铸态组织的影响

采用真空感应熔炼得到Cu-1Cr-0.1Zr和Cu-1Cr-0.1Zr-0.14La合金铸锭,采用金相显微镜(OM)观察了铸锭宏观晶粒组织,采用扫描电镜(SEM)、透射电镜(TEM)观察了基体中第二相种类、形貌及分布规律。结果表明:稀土La的添加能够明显细化铸锭晶粒,促进柱状晶向等轴晶转变。稀土La添加后,网状共晶Cr相变细、变短,分布更弥散,枝晶偏析现象减轻。TEM表征发现,铸态Cu-1Cr-0.1Zr合金中Zr在Cr相表面富集,抑制Cr相长大,使Cr相呈现球状;而添加稀土La后,La与Zr结合,减弱了Zr对Cr相的球化作用,导致Cr相沿着基体<110>方向生长并呈现棒状。铸态Cu-1Cr-0.1Zr合金主要存在的相有:网状共晶Cr相、球形Cr相和椭球形Cu_(5)Zr相,而添加0.14%La后,主要存在网状共晶Cr相,棒状Cr相、棒状CuCrZr三元相和富La相。

Effects of conform continuous extrusion and heat treatment on the microstructure and mechanical properties of Al–13Si–7.5Cu–1Mg alloy

The effects of conform continuous extrusion and subsequent heat treatment on the mechanical and wear-resistance properties of high-alloying Al–13Si–7.5Cu–1Mg alloy were investigated.The microstructures of alloys before and after conform processing and aging were compared by transmission electron microscopy and scanning electron microscopy,respectively.The results reveal that the primary phases were broken and refined by intense shear deformation during conform processing.After the conform-prepared Al–13Si–7.5Cu–1Mg alloy was subjected to solid-solution treatment at 494℃for 1.5 h and aging at 180℃for 4 h,its hardness improved from HBS 115.8 to HBS 152.5 and its ultimate tensile strength increased from 112.6 to 486.8 MPa.Its wear resistance was also enhanced.The factors leading to the enhanced strength,hardness,and wear resistance of the alloy were discussed in detail.

微量氧环境下热处理温度对Zr-1%Nb合金力学性能的影响

采用扫描电镜、X射线衍射仪及万能试验机等研究了微量氧环境下400、800和1200℃不同温度保温300 s对Zr-1%Nb合金力学性能的影响。结果表明:与未热处理的合金相比,400℃热处理后Zr-1%Nb合金的力学性能未发生明显变化;800℃热处理后,合金的塑性降低,压缩时外表面产生大量微裂纹;1200℃热处理后,压缩时合金出现了脆性断裂。热处理后合金样品的表面发生了氧化,氧化产物主要为ZrO2相。随着热处理温度的升高,Zr-1%Nb合金的氧化程度逐步加深,并且1200℃热处理后试样氧化层的厚度显著增加,内部出现大量裂纹。

预变形对Al-Cu-Li-Mn-Zr合金的第二相析出及力学性能的影响

采用维氏硬度、常温拉伸及透射电子显微镜等测试手段,研究了不同预变形状态对Al-Cu-Li-Mn-Zr合金中第二相析出行为及力学性能的影响。结果表明,未经预变形的峰值时效态Al-Cu-Li-Mn-Zr合金的析出相有T_1(Al_2CuLi)相、θ′(Al_2Cu)相,且存在极少量的χ(Al_5Cu_6Li_2)相。预变形的引入使T_1相的析出量显著增加,同时抑制了θ′相的形成,但对χ相的析出量的影响却较小。由此可知,经预变形的合金在峰值时效态的析出相以细小弥散的T_1相为主。经定量统计可知,预变形量越大,作为主要析出相的盘片状T_1相的直径越小,但厚度及体积分数几乎保持不变。此外,随着预变形量的增大,峰值时效态合金的屈服强度和抗拉强度升高,塑性降低。

Microstructure and mechanical properties of Al-5.8Mg-Mn-Sc-Zr alloy after annealing treatment

An A1-5.8Mg-0.4Mn-0.35（Sc＋Zr） （mass fraction, %） alloy sheet was prepared using water chilling copper mould ingot metallurgy processing which was protected by active flux. The influence of stabilizing annealing on mechanical properties and microstructure of the cold rolling sheet was studied. The results show that the strength and hardness of the alloy decrease, while the elongation increases with increasing the stabilizing annealing temperature. With the increase of stabilizing annealing time, the strength and hardness of the alloy drop slightly but its ductility exhibits no change. Partial recovery and recrystallization orderly occur with the increase of annealing temperature during stabilizing treatment. Only different degrees of recovery occur in the alloys annealed below 400 ℃ for 1 h. Partial recrystallization occurs after annealed at 450 ℃ for 1 h. By annealing at 300 ℃ for 1 h, the alloy can obtain the optimum application values of δb, δ0.2 and δ, which are 436 MPa, 327 MPa and 16.7%, respectively.

工艺处理对Cu-0.8Cr-0.1Zr合金组织及性能的影响

研究了不同加工工艺及热处理工艺对Cu-0.8Cr-0.1Zr合金组织和性能的影响,通过组织和性能的对比得出了最佳的处理工艺。试验结果表明,Cu-0.8Cr-0.1Zr合金经过热挤变形后,在980℃保温40min后水冷,再经460℃时效3h,Cu-0.8Cr-0.1Zr合金的电导率和硬度(HV0.2)分别达49.01MS/m、131。

高锆含量Cu-1%Zr-0.15%Ce合金热变形行为研究

利用Gleeble-1500D热模拟机,在温度为550,650,750,850,900℃,应变速率为0.001,0.01,0.1,1,10 s^(-1)的条件下,对Cu-1%Zr-0.15%Ce合金的高温变形过程中的流变应力进行研究,分析了动态再结晶的演变机制。结果表明:变形温度和应变速率对合金的流变应力有显著的影响,在550~750℃之间具有典型的动态回复特征,850~900℃具有动态再结晶热变形特征。通过流变应力、应变速率和变形温度之间的关系,建立高温热变形流变应力本构方程,得到合金的热激活能为430.51 k J·mol^(-1),与纯铜热压缩变形过程相比,高Zr含量Cu-1%Zr-0.15%Ce合金热激活能提高了105%。