SiC_p/2024与2219铝合金电子束焊接

分别采用电子束对中焊、偏束焊技术,研究了Si C颗粒增强铝基复合材料Si Cp/2024与2219铝合金的接头组织及力学性能.结果表明,对中焊时接头易出现Si C增强相的偏聚,同时发生严重的界面反应,生成大量脆性相Al4C3,接头抗拉强度最高为104 MPa.采用偏束焊工艺可以很好地抑制界面反应,通常只在焊缝上部与Si Cp/Al热影响区上部生成少量脆性相Al4C3,接头抗拉强度最高可达131 MPa.试件均断裂在母材界面反应层上,且为明显的脆性断裂.不同工艺下接头横截面硬度分布存在突变区,该区域在Si Cp/2024熔合区附近,该处脆性相Al4C3的生成导致硬度升高.     

SiC_p/2024Al复合材料界面的表征及评价（英文）

采用粉末冶金方法制备体积分数为35%的Si Cp/2024 Al复合材料。利用高分辨透射电镜对复合材料中Si Cp与Al基体、析出相与Al基体之间的界面微结构进行表征,采用拉伸弹性模量和布氏硬度测试对界面状况进行评估。结果表明,所得复合材料中Si C与Al的界面整体状况良好。复合材料中SiC/Al界面分为3种类型:大部分干净界面、少量轻微反应型界面以及极少量的非晶层界面。在干净界面中,Si C和Al的结合机制为紧密原子匹配形成的半共格界面,且Si C和Al无固定或择优的取向关系。在轻微反应型界面中,MgA l2O4尖晶石与Si C和Al均形成半共格界面,作为中间媒介很好地连接Si C和Al。复合材料经510°C固溶2 h再在190°C时效9 h后,许多圆盘状纳米析出相和棒针状纳米析出相弥散分布于基体中,且与基体的界面为错配度较小的半共格界面。此时,复合材料的布氏硬度达到峰值。     

纳米SiC颗粒增强镁基复合材料半固态搅拌法制备工艺优化

采用半固态机械搅拌铸造法,制备了增强体平均粒径50 nm的Si C颗粒增强镁基复合材料(n-Si Cp/Mg9Al),分别对不同质量分数纳米颗粒、不同搅拌时间和不同搅拌温度时,复合材料的微观组织和力学性能进行了研究。结果表明,随着Si C含量的增加,合金基体组织先细化后又出现变粗的现象,适当延长搅拌时间能更有效地细化组织,在较低温度下搅拌可以更明显地细化复合材料的微观组织。合金抗拉强度随着Si C含量的增加先增加后降低,在Si C含量为1.5%时最好,为198 MPa。在含量为2%时又有所降低,但是高于不加Si C时。搅拌时间为15 min时,复合材料的屈服强度、抗拉强度较之基体分别提高了12.8%、22%,断后伸长率由基体合金的2%提升到4%。继续延长搅拌时间到30 min,材料的室温拉伸性能出现明显恶化。不同搅拌温度下Si Cp/Mg9Al纳米复合材料与铸态Mg9Al合金相比其室温拉伸性能有明显提高,搅拌温度为600℃的Si Cp/Mg9Al纳米复合材料的室温拉伸性能最好,其屈服强度、抗拉强度和断后伸长率分别为106 MPa、155 MPa和4%。     

挤压加工对SiCp／Al复合材料组织和性能的影响

开展了挤压加工对 Si Cp/ Al复合材料显微组织和力学性能的实验研究。结果表明 :挤压加工有助于提高 Si C颗粒分布的均匀性 ,挤压棒料中的 Si C颗粒在挤压方向上定向、有序地排列 ,呈现出带状组织的特征 ;挤压加工还可以消除 Si Cp/ Al复合材料毛坯中的显微疏松缺陷 ,改善铝合金基体对 Si C颗粒损伤的容限性能 ,从而大幅度地提高复合材料的强度和塑性     

二次热压变形工艺对粉末冶金SiC_p/Al复合材料组织均匀性的影响

采用粉末冶金法在普通空气加热炉中烧结制备了不同 Si C含量的 Si Cp/ Al复合材料 ,并对其组织的均匀性作了研究。结果表明 ,对 Si Cp/ Al复合材料进行二次热压变形 ,可改善复合材料组织的不均匀性 ,使基体晶粒细化 ,Si C颗粒分布均匀 ,致密度提高。通过对不同热压工艺进行比较 ,发现 40 0℃× 190 k N× 10 min热压变形工艺对改善 Si Cp/ Al复合材料组织的不均匀性效果更好。     

双相多尺度镀镍碳纤维和碳化锆颗粒增强铝基复合材料制备及力学性能研究

采用放电等离子体烧结制备了双相多尺度镀镍碳纤维和碳化锆颗粒增强铝基复合材料(Cf(Ni)-Zr C/2024Al)。为了提高碳纤维和基体的界面结合强度,对碳纤维进行了化学镀镍,研究了烧结工艺对复合材料的密度、显微硬度和拉伸强度的影响。结果表明,在烧结温度为480℃,烧结压力为30 MPa,保温时间为10 min时,可以得到结构致密,性能优异的铝基复合材料。复合材料的密度仅为2.71 g/m~3,显微硬度、拉伸强度和伸长率分别为105.6 HV、330 MPa和10.2%,力学性能均高于2024Al合金。力学性能的提高归因于表面化学镀碳纤维和基体良好的界面结合、ZrC的网状分布结构、以及增强相和基体热膨胀系数不匹配导致的位错增强。     

机械搅拌制备SiC_p/AlSi7Mg2复合材料性能研究

采用机械搅拌制备SiC_p/Al Si7Mg2复合材料,对比不同体积分数(3.5vol.%、10vol.%、20vol.%和25vol.%)的Si C颗粒对复合材料力学性能的影响,当α-Si C颗粒的粒径为20μm时,20vol.%SiC_p/Al Si7Mg2复合材料铸态力学性能较高,其硬度达到HB 76.3。将20vol.%SiC_p/Al Si7Mg2复合材料做538℃/10 h+160℃/6 h热处理以后进行拉伸试验,复合材料抗拉强度311 MPa,屈服强度290 MPa,硬度HB 142,弹性模量90 GPa。进一步研究复合材料可重熔性,20vol.%SiC_p/Al Si7Mg2复合材料经过一次重熔后相比原铸态复合材料屈服强度提高了14.6%,硬度提高了8.8%,继续对熔体进行不同时间的静置和二次重熔,复合材料力学性能下降。     

SiC体积分数和热处理对SiC/2024Al复合材料性能的影响

采用直接电热粉末半固态触变成形法制备Si C不同体积分数(10vol%、20vol%、30vol%、40vol%)的Si C/2024Al复合材料。利用扫描电镜观察复合材料的微观组织,通过检测其物理性能和力学性能,获得Si C体积含量和热处理对Si C/2024Al复合材料组织与性能的影响规律。结果显示:随着Si C体积含量的增大,复合材料的组织出现了程度不一的Si C颗粒团聚,使材料的致密度下降;经过T6热处理后,Si C/2024Al复合材料抗拉强度在20vol%时达到最大值(505 MPa),比完全退火态提高了68.3%;布氏硬度在40vol%达到最大值(244 HB),比完全退火态提高了41.0%。     

钛合金与铝基复合材料钎焊接头组织及力学性能

通过一种超声辅助钎焊连接方法,采用Zn基钎料对TC4钛合金和55%Si Cp/Al复合材料进行了钎焊连接。通过扫描电镜、能谱议及电子万能试验机对钎焊接头的微观组织、界面成分及接头的剪切强度进行了分析研究。结果表明,超声辅助钎焊连接方法可以有效实现钛合金与55%Si Cp/Al复合材料的冶金连接。接头中复合材料侧界面氧化膜完全消失,并且基体中的小尺寸Si C颗粒向钎缝中大量迁移。而在钛合金侧界面处只生成了一种金属间化合物Ti Al3,平均厚度为2~4μm。在420℃焊接时接头的最高剪切强度可达到167 MPa,其试样接头断裂于金属间化合物Ti Al3和55%Si Cp/Al复合材料的界面区附近。     

真空热压法制备2024Al/Gr/SiC复合材料的显微组织和力学性能（英文）

采用真空热压法制备了2024Al/Gr/SiC复合材料,其中SiC颗粒和鳞片状石墨(Gr)的体积分数分别为5%~10%和3%~6%。采用光学显微镜、扫描电镜、硬度和拉伸性能测试研究SiC颗粒和石墨对分别经160、175和190°C时效处理后复合材料显微组织和力学性能的影响。结果表明:加入SiC颗粒和石墨能明显加速第二相时效析出,但SiC颗粒对时效行为的影响比石墨大。复合材料的拉伸强度和伸长率随着SiC颗粒和石墨含量的增加而降低,石墨对伸长率的影响比SiC颗粒更大。2024Al/3Gr/10SiC复合材料在165°C时效8 h时的抗拉强度、屈服强度和伸长率分别为387 MPa,280.3 MPa和5.7%。2024Al/Gr/SiC复合材料的断裂机制为基体韧性断裂和复合相颗粒与基体间撕裂断裂。     

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.     

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.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

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.