焊接热输入对纯铜焊缝组织及其力学性能的影响

在纯铜(T2)钨极氩弧自动焊(TIG)条件下,研究了不同焊接热输入对焊缝成形、焊缝显微组织及力学性能的影响。结果表明:焊接热输入过大,焊缝正面出现咬边,焊缝反面过宽、余高过高,而焊接热输入过小焊缝未焊透,轧制时易出现根部裂纹;随着焊接热输入的增大,焊缝区以及热影响区晶粒尺寸都增大,接头塑性降低;焊后未轧制时,焊接热输入越大,接头强度越低,而轧制后,焊缝的抗拉强度没有明显的变化,焊接热输入小时的屈服强度明显高于焊接热输入大时的屈服强度,并且接头断裂均发生在焊缝熔合线区,说明熔合线区是整个焊接接头最为薄弱的环节。     

不锈钢薄板大间隙接头激光-MIG电弧复合高速焊接工艺

采用填充ER316焊丝的光纤激光-MIG电弧复合焊方法,焊接间隙为0.5 mm、厚度为1 mm的SUS444铁素体不锈钢薄板对接接头和搭接接头,研究了获得成形良好的对接接头和搭接接头的工艺参数窗口和极限焊接速度,并对焊缝进行了着色渗透检验和拉伸试验. 结果表明,合理匹配焊接速度和焊接电流,是获得成形良好的大间隙接头的关键;当焊接速度过小或焊接电流过大时,较大的热输入导致焊缝过度熔透,焊缝成形不良;当焊接速度过大或焊接电流过小时,较小的热输入导致焊缝未熔透. 对接接头焊缝成形质量良好且熔透的极限焊接速度可达12 m/min,而搭接接头的极限焊接速度为5 m/min. 成形良好的焊缝均未发现表面裂纹. 拉伸试验表明,对接接头断裂在母材上;搭接接头绝大部分断裂在熔合线附近,极限焊接速度下获得的搭接接头的抗拉强度是母材的84.2%.     

Si_p/Al复合材料激光钎焊特性与组织形态

采用激光填丝钎焊方法进行1.5 mm厚65%(体积分数)Sip/4032Al复合材料对接接头的连接,研究不同工艺参数下的钎料润湿铺展行为和焊缝成形特性,以及焊缝中共晶硅的形态变化规律。结果表明:接头开V型坡口非常有利于焊缝的背面成形;光斑直径为20 mm、激光功率高于1 500 W时焊缝成形容易控制;与激光熔焊相比,激光钎焊方法更适合于连接高比分Sip/4032Al复合材料。焊接热输入对Si元素的溶解、扩散行为影响很大,因此,不同激光功率下,焊缝中硅元素可以板状、多角状、瓣状初生硅、板条状共晶硅等多种形态出现。焊缝中心由于冷却速度较慢,还形成了共晶团组织,共晶团内部为均匀分布的短棒状共晶硅。     

超细晶粒钢低热输入背面辅助成形焊接工艺研究

对400 MPa级超细晶粒钢进行STT焊接电源下的CO2气体保护焊,采用低热输入窄坡口自制焊剂垫背面辅助成形工艺得到焊缝成形美观、根部和侧壁熔合良好以及热影响区极窄的焊接接头。研究结果表明:低热输入窄坡口条件下,焊剂垫只起引弧作用而不起强迫成形作用,只用熔敷金属的自重以及电弧吹力的作用来达到辅助成形目的;小曲率焊剂垫更利于加大电弧扩展角,使得焊缝成形更为合理。在低热输入窄坡口背面辅助成形工艺下所得接头力学性能均优于母材,焊缝区是因为焊材的合理选择。扫描电镜观察显微组织发现HAZ生成了晶粒较小不同方向不同晶界的多种非平衡组织,尤其是出现了能改善力学性能的粒状珠光体。     

CO_2激光焊接600MPa DP钢接头组织与性能

采用CO2激光对抗拉强度为600MPa,厚度1.4mm的DP钢进行焊接.研究焊接速度对焊缝外观和截面成形的影响、接头的组织特点、硬度、强度和成形能力.结果表明,激光功率相同,焊接速度较低时焊缝易产生气孔,焊接速度较高时易发生飞溅;焊接速度对焊缝熔深及熔宽也有影响.焊缝区组织主要由马氏体构成,从焊缝、焊接热影响区到母材,组织中马氏体含量下降,接头的最高硬度出现在焊缝或热影响区.在平行于焊缝方向,焊接接头的抗拉强度高于母材,垂直于焊缝方向,接头的抗拉强度与母材相当.由于焊缝出现马氏体组织,接头的塑性和韧性降低,板材的冲压成形能力下降.     

高速列车铝合金车体典型接头激光-MIG复合焊接特性研究

针对传统高速列车3 mm厚A6N01S-T5铝合金型材典型接头结构开展激光-MIG复合焊接试验,优化复合焊接工艺参数,分析接头组织性能,研究激光-MIG复合焊的工程适应性。结果表明,在最佳工艺参数下,焊缝成形良好、无气孔缺陷。焊缝中心为树枝状铸态组织,靠近熔合线焊缝为柱状晶组织,熔合区较窄但热影响区存在晶粒轻微粗大现象;焊缝区硬度低于母材区,硬度最小值位于熔合线附近的热影响区;最佳工艺参数下接头的平均抗拉强度为204.6 MPa,达到母材的83.5%;断裂发生在熔合线附近,断口形貌呈现典型的塑性断裂特征;接头的弯曲性能良好;组对间隙小于1.0 mm时,最佳工艺参数具有通用性,焊缝成形及接头抗拉强度良好;组对间隙增至1.5 mm时,优化工艺参数焊缝成形及接头抗拉强度依然良好。结果表明,激光-MIG复合焊对高速列车铝合金车体典型接头具有良好的焊接可行性和工程适应性。     

6061-T6铝合金MIG焊接工艺研究

以4 mm厚6061-T6铝合金轧制板材为研究对象,通过改变焊接线能量与送丝速度,研究了不同工艺参数下接头的显微组织和力学性能。结果表明,HAZ宽度和熔合区晶粒大小随线能量的增大而增大;当线能量为297 J/mm时焊接接头的抗拉强度为213 MPa,达到母材强度的73%。熔宽对送丝速度的变化较余高和熔深更敏感,送丝速度位于7.4~8.2 m/min范围内时,焊缝成形较好;在送丝速度为8.3 m/min时获得最大的抗拉强度239 MPa。断裂发生在热影响区,属于韧性断裂,表明热影响区为焊接接头最薄弱的位置。     

Nd:YAG激光焊接800 MPa TRIP钢的接头组织与性能

采用Nd:YAG激光对强度为800MPa,厚度为1.2mm的TRIP钢板进行焊接.研究焊接速度对焊缝外观和截面成形的影响及接头的组织特点、硬度、强度和成形能力.激光功率相同,焊接速度较低时焊缝易产生气孔,速度较高时易发生飞溅;焊接速度对焊缝熔深及熔宽也有影响.焊缝组织主要由马氏体构成,从焊缝、热影响区到母材,组织中马氏体含量下降,接头的最高硬度出现在焊缝或热影响区.在平行于焊缝方向,焊接接头的抗拉强度高于母材,垂直于焊缝方向,接头的抗拉强度与母材相当.由于焊缝中出现马氏体,接头的塑性和韧性降低,板材的冲压成形能力下降.     

400MPa球墨铸铁光纤激光-MIG电弧复合焊接头的断裂特征

采用填充308L不锈钢焊丝光纤激光-MIG电弧复合焊方法,焊接厚度为5mm的风电关键部件用400 MPa级球墨铸铁,获得了表面成形良好且熔透的焊缝,研究了MIG电弧热输入对接头拉伸性能和断裂特征的影响.结果表明,电弧热输入较小时,接头的拉伸性能差,断裂沿熔合线发生,断口为脆性断口;电弧热输入较大时,接头的拉伸性能较好,断裂自半熔化区顶部沿母材发生,断口顶部为脆性断口,底部为韧性断口.接头断裂特征的差异是由接头中焊缝和半熔化区底部莱氏体的量的不同导致的.基于以上研究,获得了抗拉强度为346.4 MPa、断后伸长率为5.4％,断裂发生在母材上的优质接头.     

高氮奥氏体焊丝焊接超高强钢接头组织和性能

为解决超高强钢焊接冷裂纹问题,采用强度低于母材的高氮奥氏体丝材进行GMAW工艺试验,研究在不同坡口角度下超高强钢焊接接头组织性能. 结果表明,采用该焊丝获得的接头焊缝成形良好,焊缝截面未见裂纹缺陷. 熔合线附近组织主要为针状和板条状马氏体,焊缝组织主要为奥氏体及被奥氏体基体所包围的铁素体树枝晶. 熔合线附近马氏体区硬度平均值为530 HV;焊缝区硬度平均值为275 HV. 相对于60°坡口接头,90°坡口接头熔合线附近马氏体组织硬度更高. 90°坡口接头的抗拉强度平均达到850 MPa,最高达887 MPa,而60°坡口接头抗拉强度平均仅为690 MPa.     

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.     

新型的治疗阿尔茨海默氏症药物(1-二甲基磷酰基-2,2,2-三氯)-乙基-1-醇烟酸醋对体外神经细胞的作用

目的: 观察本实验室合成的一种治疗阿尔茨海默氏症(AD)的药物(1-二甲基磷酰基-2, 2, 2 -三氯)-乙基^-1-醇烟酸醋(NMF),对体外培养的皮层神经细胞活性的影响以及对海人藻酸(KA)所致的神经损伤的保护作用。方法: 采用体外培养皮层神经元的方法,解剖分离 15 d胚胎小鼠皮层神经细胞, 接种于 96孔板,48 h 后加药并培养 72 h,以 MIT 法 观察 NMF 对小鼠皮层神经细胞活性的影响;同时将接种于 24 孔板的细胞预先给予 NMF,d 3 时加或不加KA处理后,以台盼蓝染色鉴别并计数死、活细胞,可得出细胞的存活率。结果: NMF 明显促进胎鼠皮层神经元活性,其中 NMF1、0. 1、10nmol·L^-1促进神经元活性增殖率分别高达 34.7%、37.4%、36. 7%, NMF 明显促进正常胎鼠皮层神经元存活卒,与对照组比较,10nmol·L^-1 NMF 对皮层神经元的存活率分别提高 39.3%、73.5%。 NMF能显著 对抗 KA 所致的神经元损伤,与 KA 损伤组相比, NMF0.1、10、10nmol·L^-1对损伤皮层神经元的保护率分别为 77.30%、80.10%、84.15%。结论: NMF 明 显促进胎鼠皮层神经元的洁性、提高正常皮层神经元,的存活卒,并能有效地保护KA所致的神经元损伤,提示 NMF 是一种很有潜力的治疗 AD 的药物。     

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.     

Three-Dimensional Growth of Coherent Ferrite in Austenite: A Molecular Dynamics Study

Coherent second phase often exhibits anisotropic morphology with specifi c orientations with respect to both the second and the matrix phases. As a key feature of microstructure, the morphology of the coherent particles is essential for understanding the second-phase strengthening eff ect in various industrial alloys. This letter reports anisotropic growth of coherent ferrite from austenite matrix in pure iron based on molecular dynamics simulation. We found that the ferrite grain tends to grow into an elongated plate-like shape, independent of its initial confi guration. The fi nal shape of the ferrite is closely related to the misfi t between the two phases, with the longest direction and the broad facet of the plate being, respectively, consistent with the best matching direction and the best matching plane calculated via the Burgers vector content(BVC) method. The strain energy calculation in the framework of Eshelby's inclusion theory verifi es that the simulated orientation of the coherent ferrite is energetically favorable. It is anticipated that the BVC method will be applicable in analysis of anisotropic growth and morphology of coherent second phase in other phase transformation systems.     

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).     

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.