等通道角挤压制备细晶ZK60镁合金的组织与力学性能

利用两种等通道角挤压(ECAP)方法(普通单步ECAP和两步ECAP)制备细晶ZK60合金。采用金相显微镜、扫描电镜、透射电镜和X射线衍射仪对合金的组织和织构进行观察,通过拉伸试验研究不同ECAP方法对合金力学性能的影响。结果表明:与单步ECAP变形相比,两步ECAP变形,由于降低了变形温度,晶粒细化效果更好;经过(240℃,4道次)+(180℃,4道次)两步ECAP变形后,合金晶粒细化至约0.8μm;合金的力学性能与材料的织构密切相关,由于存在织构软化效应,与挤压态相比,经单步ECAP变形后合金的强度有所降低,而伸长率明显提高;但经两步ECAP变形后,由于细晶强化和亚结构强化的作用,合金的强度得到提高。     

等通道转角挤压制备超细晶Mg15A1双相合金组织与性能

对高铝双相合金Mg15A1在553K以Bc路线进行了不同道次的等通道挤压（ECAP）,获得了超细晶高铝镁合金。通过OM,SEM,TEM分析了ECAP前后合金的微观组织结构及断口形貌,并测试了不同挤压道次后合金的硬度和室温拉伸性能,分析了ECAP细化晶粒机理及其性能改善原因。结果表明,随挤压道次增加,累计形变增强,网状硬脆相β-Mg17Al12破碎,合金晶粒显著细化,但对单相区和两相混合区细化效果不同。在α、β两相共存区内,4道次ECAP后形成100nm-200nm的细晶粒;在α单相区,4道次ECAP后晶粒为1μm以下,且在初晶α-Mg内析出弥散细小的β相,起到细晶强化和弥散强化作用。8道次ECAP后,晶粒略有长大。ECAP使合金的硬度、抗拉强度和延伸率同时得到提高,尤其是4道次ECAP后,硬度提高了32．04％,抗拉强度σb从150MPa提高到269．3MPa,延伸率δ由0．05％提高到7．4％;8道次ECAP后,硬度、抗拉强度略有下降,延伸率略有上升。SEM断口观察显示ECAP使合金拉伸断口形貌由铸态的解理断裂特征转变为延性韧窝断裂特征。     

双相合金Mg-8Li-1Al的等通道转角挤压Ⅱ.挤压后合金的室温拉伸性能

随着等通道转角挤压(ECAP)次数的增加，Mg-8Li-1Al(质量分数，％)合金的室温拉伸强度和塑性同时增加，对应1，2，3，4次ECAP，合金的屈服强度分别为169，185，196和198MPa，延伸率分别为12％，14％，25％和27％，微观组织分析表明，ECAP方法在细化两相组织、提高合金强度的同时，还改善了α相组织的均匀性和等轴性，并使各晶粒间的取向差逐渐增大，这种处在非平衡状态的、具有较大取向差的晶界结构，在室温拉伸变形过程中可激活晶界滑移或晶粒转动等变形方式，进而使材料的塑性随道次增加而得到提高。     

等径角挤压Al-4%Mg-0.3%Ce合金的拉伸及断裂行为

对Al-4％Mg-0．3％Ce合金进行了不同道次和路径的等径角挤压（ECAP）加工,对其所加工样品在室温下进行了10^-4～10^-1s^-1不同应变速率的拉伸试验及其断口观察,探讨了ECAP合金的室温拉伸及断裂行为,并与常规热挤压进行了对比分析。结果表明,ECAP合金表现出更高的室温屈服强度,经过不同道次和路径ECAP的合金的拉伸断裂方式为切断型,而常规热挤压合金的拉伸断裂方式则为正断型。     

ECAP变形对Mg-4.5Zn-1Ca合金显微组织及腐蚀性能的影响

采用OM、SEM、XRD对铸态和等通道角挤压(ECAP)变形后Mg-4.5Zn-1Ca(wt%)合金的微观组织进行了表征。通过电化学工作站和浸泡法评估了ECAP变形前后合金在模拟体液(SBF)中的腐蚀性能。结果表明,铸态Mg-4.5Zn-1Ca合金显微组织由α-Mg基体及分布在晶界处和晶粒内的Ca2Mg6Zn3相组成,平均晶粒尺寸为86μm。经ECAP变形后,合金的晶粒尺寸得到显著细化,经6道次ECAP变形后的平均晶粒尺寸为5μm。随着ECAP变形道次的增加,第二相在镁基体中的分布更加均匀、弥散。ECAP变形后合金更容易发生腐蚀,挤压道次越多,合金的自腐蚀电位越负,自腐蚀电流越大,即耐蚀性越差。经6道次ECAP变形后合金的自腐蚀电位最负(-1.42 V),自腐蚀电流最大(407.38μA/cm~2),耐蚀性最差。     

ECAP变形对Mg-Y-Nd-Zr合金组织和性能的影响

利用等通道角变形(ECAP)方法,沿Bc路径在400℃温度下对稀土Mg-2Y-0.6Nd-0.6Zr合金进行不同道次的塑性变形,采用光学显微镜,X射线衍射仪和电子背散射衍射(EBSD)技术等分析了不同道次挤压之后合金的微观组织、晶粒尺寸、物相和织构的变化,采用硬度试验和拉伸试验研究了ECAP不同道次对合金力学性能的影响。结果表明:ECAP之后Mg-2Y-0.6Nd-0.6Zr合金晶粒得到明显细化,并且在4道次之后晶粒细化效果最佳,大部分晶粒已细化至0.45μm;在ECAP变形6道次后再结晶的晶粒开始长大,但晶粒组织在6道次的时候均匀性最好;Mg-2Y-0.6Nd-0.6Zr合金第二相体积分数较小,ECAP变形后有大量的第二相粒子Mg_2Y相从过饱和的基体中析出且多分布于晶界处,ECAP变形4道次后各相数量趋于稳定;Mg-2Y-0.6Nd-0.6Zr合金随着挤压道次的增加,小角度晶界所占比例减少,大角度晶界有所增加;同时,进行ECAP变形后,Mg-2Y-0.6Nd-0.6Zr合金织构的强度和取向都有所变化,织构强度在4道次时最弱,在随后的ECAP变形中又开始增强,在6道次时由倾斜织构转变成强基面织构,Schmind因子趋于0,力学性能结果表明晶粒的细化作用大于织构的软化作用和强化作用,随着ECAP道次的增加,Mg-2Y-0.6Nd-0.6Zr合金的力学性能有所提高,但是在ECAP变形4道次后提高幅度较小,抗拉强度由150 MPa提高到183 MPa,硬度也从54.8 HV0.1提高到了63.7 HV0.1,屈服强度也较ECAP变形之前提高了56%,基本上符合Hall-Petch关系;并且在6道次后,由于晶粒细化且均匀分布,室温伸长率提高到了26.7%。     

扩展路径低温ECAP及时效热处理对Cu0.6Cr合金的组织和性能影响

采用光学显微镜和X射线衍射仪对Cu0.6Cr合金经低温扩展路径等通道转角挤压（ECAP）后的组织演变规律进行了研究。采用扫描电子显微镜和能谱仪研究了Cu0.6Cr合金经不同时效热处理条件后的晶粒大小、析出相分布规律和断裂特征。并且分别测试了合金经低温ECAP和低温ECAP+时效热处理后的抗拉伸强度、硬度和导电率。结果表明,Cu0.6Cr合金经低温ECAP变形后形成明显细化且相互交割的纤维组织,并且合金在变形中始终保持（111）面的择优取向。时效热处理的合金变形量越大,析出相的数目和尺寸就越大,第二相析出速率也越快。5道次合金经450 ℃时效2 h后的抗拉伸强度为568.1 MPa,维氏硬度为1624.8 MPa,导电率为82%IACS。     

等通道转角挤压对Mg-6Zn合金显微组织和力学性能的影响

利用等通道转角挤压(ECAP)技术,在200℃对Mg-6Zn合金进行了不同道次的挤压。结果表明,经ECAP挤压后合金显微组织明显细化、均匀化,平均晶粒尺寸由15μm减小到3μm;ECAP过程中粗大的块状共晶相变形破碎、细化,并在周围诱发新相析出。通过XRD分析发现析出相主要是Mg_4Zn_7和MgZn_2。经过2道次ECAP挤压后,Mg-6Zn合金的抗拉强度可达275 MPa,屈服强度达到245 MPa,伸长率为24%。当ECAP道次增加到4道次和6道次后,强度反而下降。     

Al-Zn-Mg-Cu铝合金ECAP变形后的组织和性能

通过对退火态的Al-Zn-Mg-Cu系铝合金在523 K加热进行不同道次等径通道挤压(ECAP),采用120°模具在Bc路径下经10次ECAP变形后等效真应变达到6.2.试验结果表明,退火态合金试样ECAP挤压后晶粒明显细化,8道次之后晶粒细化趋于缓和,10道次后获得晶粒尺寸为0.8 μm左右的等轴状组织.性能测试结果表明:合金的显微硬度、抗拉强度及伸长率随着ECAP变形道次的增加而增大,ECAP提高了合金的综合力学性能,显著地改善了合金的塑性.     

ECAP对连铸Cu-Ag合金断口形态及力学性能的影响

采用连续铸造和等径角挤压变形(ECAP)加工集成技术制备Cu-Ag合金,研究其力学性能和相应的拉伸断口形态。研究发现,Cu-Ag合金的强度随着ECAP加工道次和Ag含量的增加而增加,而延伸率却下降。连续铸造和ECAP加工的合金与传统浇铸和ECAP加工的合金相比,缩颈前静态韧性有所提高。同时发现,只有连铸的Cu-Ag合金在断裂前表现出缩颈现象,而经ECAP挤压后试样的断裂变为剪切模式,随着ECAP道次的增加出现不同的剪切断裂角。基于实验结果,讨论了经ECAP挤压后连铸Cu-Ag合金的拉伸断裂机制。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.