Mg和Zn对2099合金时效组织与拉伸性能的影响

通过常规力学性能测试和透射电镜微观组织观察,研究2099合金在不同热处理状态(T6和T8)下的微观组织和拉伸性能,以及2099合金中所含少量Mg和Zn对合金组织与性能的影响。结果表明:2099合金在T6峰时效条件下,主要强化相是δ′相、θ′相和T1相;在T8峰时效下,主要强化相是δ′相、T1相和少量θ′相,预拉伸变形促进T1相的析出,提高合金的时效强化效果;Mg的添加促进GP区和θ′相的析出,Zn的添加有利于T1相生成和弥散分布;而Mg和Zn同时添加显著地促进T1相析出,并抑制δ′相的粗化。     

2A97铝锂合金双级时效研究

通过TEM分析和常规力学性能测试,研究双级时效工艺对2A97铝锂合金组织和性能的影响,以优化合金强度和塑性匹配。结果表明:随预时效温度升高,双级时效基体由形成θ′/θ″相和δ′相为主的组织转变为形成T1相、θ″/θ′和δ′相为主的组织。135℃预时效、双级时效基体形成大量细小的θ′/θ″相和δ′相,T1数量少。晶界和亚晶界T1数量多,尺寸小,晶界和亚晶界θ′/θ″无析出带宽度窄。155℃预时效、双级时效可在基体形成以T1相为主的组织,且数量多,尺寸大,均匀分布,T1相、θ″/θ′和δ′相的联合强化作用使合金具有高的强度。     

Zn/Mg对Al-Zn-Mg合金时效析出惯序的影响

制备了Al6.2Zn2.3Mg和Al5.0Zn3.0Mg两种合金并进行了固溶时效处理,基于EET理论,计算了合金基体固溶体的价电子结构,研究了Zn/Mg对合金时效析出行为的影响。研究认为：Al6.2Zn2.3Mg合金固溶时优先形成的a-Al-Zn-Mg固溶体为η相析出序列GP区的形成提供了条件,合金只启动η相析出序列,故时效硬化行为表现出明显的双峰特征;而Al5.0Zn3.0Mg合金固溶时形成的a-Al-Zn-Mg和a-Al-Mg-Zn-Mg-Al两种固溶体分别为η相和T相析出序列GP区的形成提供了条件,合金时效时同时启动了时效进程不同、强化相析出与转变时间及其强化作用不同的η相和T相两个析出序列,故Al5.0Zn3.0Mg合金时效硬化双峰特征不明显。     

2198铝锂合金对时效温度敏感性及其析出行为

通过拉伸测试和透射电镜分析,研究了不同时效温度下2198铝锂合金组织和性能的变化。结果发现:在峰时效之前的小温度区间内,2198铝锂合金对时效温度非常敏感,经淬火变形后在150~170℃下时效14 h,随温度的升高,强化效果显著增加,延伸率降低;观察到的2198合金的析出相相主要是δ′、θ′、β′/δ′、T1、σ相。不同时效温度下得到的析出相的种类和形貌不同,160℃以下时效,析出相以δ′、θ′、β′/δ′为主,160℃以上,以T1、σ相的为主,多种相复合强化。时效过程中析出相的种类和含量的变化是该合金力学性能对时效温度敏感的本质原因。     

Zn/Mg比对Al-Zn-Mg合金时效析出惯序的影响

采用硬度测试研究了Al6.2Zn2.3Mg和Al5.0Zn3.0Mg合金470℃固溶2 h,再经120℃时效后的时效硬化行为。计算了Al6.2Zn2.3Mg和Al5.0Zn3.0Mg合金基体的价电子结构,研究了固溶及时效初期基体中原子团簇形成的微观机制,进而分析了Zn/Mg比对Al-Zn-Mg合金时效析出惯序的影响。研究表明:Al6.2Zn2.3Mg合金时效硬化行为表现出双峰特征的原因在于时效初期优先形成的a-Al-Zn-Mg固溶体只为η析出序列起始相GP区的形成提供了条件;而Al5.0Zn3.0Mg合金时效硬化行为不具有双峰特征的原因在于时效初期形成的a-Al-Zn-Mg和a-Al-Mg-Zn-Mg-Al 2种固溶体分别为η和T析出序列起始相GP区的形成提供了条件,因而合金时效时同时启动了时效进程、强化相析出及转变时间和强化作用不同的2个析出序列。     

微合金化对Al-Cu-Li-Zr合金拉伸性能和微观组织的影响

通过拉伸测试和TEM观察研究了Mg、Zn、Mn微合金化对Al-Cu-Li-Zr合金力学性能和微观组织的影响。结果表明:与基础合金相比,Mg、Zn、Mn微合金化的Al-3.1Cu-2.1Li-0.1Zr合金T6时效时的强度较高,峰值强度提高约40 MPa,且在低温T8时效时的时效响应速率明显加快,同时具有较低的各向异性。Al-Cu-Li-Zr合金的析出相为大量δ'相、T1相和少量θ'相。T6时效时,微合金元素的添加显著增大δ'相、T1相和θ'相的析出密度,且出现少量S'相。低温T8时效时,微合金元素的添加有效促进δ'相和T1相细小弥散地析出。     

Zn添加对预时效态Al-Mg-Si-Cu合金自然时效和烘烤硬化性的影响

以含Zn和不含Zn的2种Al-Mg-Si-Cu合金为研究对象,研究了Zn添加(0.64%,质量分数)对预时效态Al-Mg-Si-Cu合金的自然时效行为和烘烤硬化响应的影响,并利用三维原子探针(3DAP)技术揭示了相关微观机理。结果表明,含Zn合金在80℃下预时效15 min后的自然时效过程中原子团簇的Zn含量增加,原子团簇的稳定性改变,与不含Zn合金相比,含Zn合金原子团簇生长得更快。含Zn和不含Zn合金在预时效后的自然时效过程中屈服强度增加,含Zn合金因为具有更小的原子团簇间距和更大的原子团簇剪切模量,其屈服强度始终高于不含Zn合金。预时效后自然时效不同时间后在170℃下进行30 min模拟烤漆处理,原子团簇向GP区和β"相的转变随着自然时效时间的延长而减弱,因此含Zn和不含Zn合金的烘烤屈服强度降低。Al基体中的Zn具有促进析出相转变的作用,因此含Zn合金的烘烤屈服强度始终高于不含Zn合金。     

锌镁比对7085铝合金时效组织演变的影响

通过硬度和电导率测试,结合金相显微分析、透射电镜微观组织观察和DSC分析,研究了Zn/Mg比对7085铝合金120℃单级时效的影响.结果表明,120℃时效时,不同Zn/Mg比值的7085铝合金分别在4h和26 h到达GP区和(n)相强化的2个峰值,但Zn/Mg=7.27的合金两个时效峰值时间较Zn/Mg=5.84的合金略微提前.微观组织观察表明,时效4h后Zn/Mg=7.27的合金晶内已经有较多粗大的沉淀相(5～10 nm)析出,衍射斑点显示这些较大沉淀相为 η’相,而在Zn/Mg=5.84的合金内则较少发现.细小的GP区的减少以及较大 η’相的析出,降低了第二相粒子对合金的强化效果.DSC结果也表明,Zn/Mg=7.27的合金的GP区和η′相的析出温度都较Zn/Mg=5.84稍微降低.     

Ge在Al-3.5Cu合金中的微合金化作用

通过显微硬度测试、常规拉伸性能测试、透射电镜观察等研究了微量Ge(0.21%)在Al-3.5Cu(质量分数,%)合金中的微合金化作用。结果表明:175℃时效时,由于Ge与空位间有很强的相互作用,Ge的添加抑制了GP区的形成,也使随后析出的θ′′和θ′的密度减少,含Ge合金时效响应速率减小,峰值硬度和强度降低。200℃时效时,由于时效温度很高,有利于空位扩散,从而释放了Ge对空位的钉扎,使含Ge合金中总的可动空位数量增多,有利于过饱和固溶体的分解,因此含Ge合金时效响应速率反而有所加快,硬化、强化效果增大。     

Al-Zn-Mg-Cu合金时效沉淀相应变场研究

利用高分辨透射电子显微镜研究喷射成形Al12Zn2.4Mg1.1Cu合金不同时效时间析出的GPⅡ区和η′亚稳沉淀相,并结合几何相位分析软件计算了GPⅡ区和η′亚稳沉淀相的应变场。研究表明:该合金的时效硬度变化和主要析出相的变化密切相关。GPⅡ区大量弥散析出是造成合金硬度迅速上升的主要原因。η′是峰值时效状态下的主要析出强化相。析出相从GPⅡ区到η′的转变,是应变峰值较小的分散半共格应变场取代了应变峰值较大的集中共格应变场的过程。并对GPⅡ区和η′亚稳沉淀相的演变过程及强化机制进行了讨论。     

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.