Microstructure and mechanical properties of stationary shoulder friction stir welding joint of 2A14-T62 aluminum alloy

2A14-T62 butt joint was successfully welded by stationary shoulder friction stir welding(SSFSW)method.The results showed that using a pin with small shoulder could broaden the process window,and under a rotation speed of 2000 r/min and welding speed of 30 mm/min,joint with smooth surface,small reduction in thickness and little inner defects was obtained.The weld nugget zone was approx-imately circular,which was a unique morphology for SSFSW.The heat-affected zone(HAZ)and thermo-mechanically affected zone(TMAZ)were both quite narrow due to the lower heat input and slight mechanical action of the stationary shoulder.The fraction of high angle grain boundaries(HAGBs)exhibited a“W”shape along horizontal direction(from advancing side to retreating side),and the minim-um value located at HAZ.The average ultimate tensile strength and elongation of the joint were 325 MPa and 4.5%,respectively,with the joint efficiency of 68.3%.The joint was ductile fractured and the fracture surface contained two types of dimples morphology in different re-gions of the joint.Microhardness distribution in the joint exhibited a“W”shape,and the difference along the thickness direction was negli-gible.The joint had strong stress corrosion cracking susceptibility,and the slow stain rate tensile strength was 139 MPa.Microcrack and Al2O3 particulates were observed at the fracture surface.

2A14-T6铝合金厚板电子束焊接头的显微组织及力学性能

对24 mm厚2A14-T6铝合金板开展了电子束焊接试验,获得了最佳的焊接工艺参数。结果表明:接头变形小、深宽比大,探伤结果为I级。接头各微区组织具有差异性,焊缝中心组织为树枝晶,近熔合线处的焊缝组织为柱状晶,热影响区组织为粗化的扁长纤维状组织,沉淀强化相颗粒增多,过时效区组织与母材相近,均为扁长纤维状组织。焊缝区晶粒内有少量沉淀强化相,晶界上存在由铜、硅等元素与基体相形成的共晶相,呈网络状分布;母材区有细小的Al_(2)Cu沉淀强化相及呈条状分布的大块共晶相。焊缝区显微硬度最低,热影响区硬度随距焊缝中心距离增大先上升后下降,母材区的最高。接头的平均抗拉强度和断后伸长率分别为387.7 MPa和3.4%,微观断口有撕裂棱和少量大而浅的韧窝,为脆性为主的韧脆混合型断裂。

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.

2A14-T6铝合金封头焊缝断裂失效分析

针对某2A14-T6铝合金焊接结构在承压试验中发生接头断裂行为开展失效分析,采用断口扫描、宏观形貌检测、焊缝金相分析、焊接结构分析及力学旁证试验等方法,对其进行了断裂原因及机理研究。试验结果表明:焊缝断裂部位存在密集的显微气孔和少量组织疏松缺陷,降低了接头有效承载面积和组织性能,是焊缝断裂失效的主要原因;起裂源区位于焊缝打底焊漏台阶形貌焊趾处,该处接头存在过渡急剧,引起应力集中,是导致焊缝断裂失效的直接原因。在焊接工艺方面,应通过优化焊接工装、细化焊接过程控制等方式提高氦弧焊接过程的稳定性,减少空气侵入电弧,进而降低焊缝气孔率;同时应重视焊缝焊趾形貌的精细化修整,保证接头圆滑过渡,避免出现应力缺口效应。

2A14-T6铝合金棒材机加工断裂原因分析

某公司提供给用户的φ260 mm2A14-T6铝合金挤压棒材,用户按照工件尺寸首先将棒材锯切成若干等份,然后对每一段棒材机械加工成工件。用户在机械加工过程中工件发生块状崩落,同时发现工件截面出现裂纹,于是提出质量异议。本研究的目的是找出棒材机械加工工件过程中发生断裂的原因并进行深入分析,探讨后续解决问题的途径。

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.

不同焊丝2A14铝合金TIG焊接头微观组织和力学性能对比分析

分别采用BJ-380D焊丝和BJ-380A焊丝开展了2A14-T6铝合金的TIG焊接试验,对比研究BJ-380D焊丝和BJ-380A焊丝对焊接接头组织、抗拉强度和硬度的影响。结果表明:两种焊丝接头焊缝区均为典型的铸态枝晶组织,焊丝Zr、V、Cr等微合金成分的添加使得BJ-380D焊丝接头焊缝区微观组织比BJ-380A焊丝焊接接头的更加细小,同时接头抗拉强度、伸长率及显微硬度也得到一定程度的提高。BJ-380D焊丝中添加的Be元素,起到了控制焊缝中Al2O3夹杂,抑制焊缝气孔缺陷的作用。相同焊接条件下,BJ-380D焊丝焊缝组织中的微观气孔大幅降低。

Aluminothermal reaction to prepare Al-Ti-C master alloy

An investigation was carried out on the reaction process and mechanism between K 2TiF 6, graphite powder and aluminum melt with the common Ti concentration of 5%～7% in the grain refiner Al Ti C master alloys and the reaction temperature of 750～950 ℃, aiming at understanding their reaction mechanism and putting forward the aluminothermal reduction reaction method to practical use. During experimental investigation, K 2TiF 6 and graphite wrapped in aluminum foils were introduced into the aluminum melt at 850 ℃. Samples of alloy and slag were investigated by chemical analysis, XRD examination, SEM observation, and EDS analysis as well. It was found that the reaction was very vigorous at the beginning of the process and then reached a dynamic equilibrium. There were 3 particular reactions during the aluminothermal reaction process. At the beginning stage of the reaction, there emerged the phases of TiC and one type of metastable intermetallic phase TiAl 9 as well as TiAl 3 in aluminum melt. At the late stage of the reaction, the metastable phase TiAl 9 disappeared and another phase of Al 4C 3 emerged.

Structure and visible photocatalytic activity of nitrogen-doped meso-porous TiO_2 layer on Ti6Al4V substrate by plasma-based ion implantation

The nitrogen-doped porous TiO2 layer on Ti6Al4V substrate was fabricated by plasma-based ion implantation of He, O and N. In order to increase the photodegradation efficiency of TiO2 layer, two methods were used in the process by forming mesopores to increase the specific surface area and by nitrogen doping to increase visible light absorption. Importantly, TiO2 formation, porosity architectures and nitrogen doping can be performed by implantation of He, O and N in one step. After implantation, annealing at 650 ℃ leads to a mixing phase of anatase with a little rutile in the implanted layer. By removing the near surface compact layer using argon ion sputtering, the meso-porous structure was exposed on surfaces. Nitrogen doping enlarges the photo-response region of visible light. Moreover, the nitrogen dose of 8×1015 ion/cm2 induces a stronger visible light absorption. The photodegradation of rhodamine B solution with visible light sources indicates that the mesopores on surfaces and nitrogen doping contribute to an apparent increase of photocatalysis efficiency.

Effect of Brazing Conditions on Microstructure and Mechanical Properties of Al_2O_3/Ti—6Al—4V Alloy Joints Reinforced by TiB Whiskers

Al2O3 and Ti-6Al-4V alloy were brazed with Ag-Cu-Ti ＋B fillers in different brazing conditions. Effects of brazing temperature, holding time and additive Ti content on joints microstructure and shear strength were investigated by scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction, transmission electron microscopy and shear testing. Results indicate that TiCu and Ti（Cu,Al） decrease, but Ti2Cu and -Ti2（Cu,Al） increase in brazing seam with increasing brazing temperature, holding time and additive Ti content. Area consisting of Ti3（Cu,Al）30 and TiO near Al2O3 becomes gradually discontinuous from continuity when brazing temperature rises or holding time extends. As Ti additive content increases, TiO is absent near Al2O3, area consisting of only Ti3（Cu,Al）30 thickens. TiB whiskers are in situ synthesized by Ti and B atoms during brazing process. The brazing temperature, holding time and additive Ti content on joints microstructure influence the joints shear strength directly. The shear strength of joints, obtained at 850 ℃ holding for 10 min, reaches the maximum of 78 MPa. According to the experimental results, phase diagram and thermodynamics calculation, the interface evolution mechanism of the Al2O3/Ti-6Al-4V alloy joint was analyzed.

On the Selection of a Composite Material for Two-Wheeler Foot Bracket Failure Prevention through Simulation and Mathematical Modeling

A foot bracket is a metal panel bracket used to mount and support the footrest in two-wheeler systems.It holds the footrest in place while rigidly supporting it.In working conditions,this element has often been observed to fail when specific load-fluctuation conditions are established at its rear end.Appropriate materials therefore need to be identified to overcome such a recurring failure.To address these issues,the present study has been implemented with the specific objective to determine the response of selected Al6061-T6 and Al7075-T6 Hybrid Metal Matrix Composites(HMMC).The results,obtained using the ANSYS Software,show that the selected composites can withstand 636,962 N/m^(2)of maximum stress and 8.88×10^(−6)m of minimum displacement.These results are also compared with relevant mathematical models and it is concluded that the identified material combination provides the required improvement of structural stability that can withstand the load fluctuation on the foot bracket.

Corrosion behavior of Ce-doped Ni-10Cu-11Fe-6Al(wt%) inert anode in molten CaCl_2 salt

In this research the effect of cerium dopingon corrosion behavior of Ni-10 Cu-11 Fe-6 Al(wt%) alloy as a novel inert anode in titanium electrolytic production was investigated. The samples, including un-doped and Ce-doped nickel-based alloys, were prepared using vacuum induction melting(VIM) process and then exposed to the electrolysis in molten calcium chloride at 900C at à1.6 V versus graphite reference electrode for different immersion time. The surface and cross-section of the samples were characterized using scanning electron microscopy(SEM), and their electrochemical behavior was investigated by electrochemical impedance spectroscopy(EIS). The results show that the un-doped samples have greater number of voids and porosities as compared to that of the 0.0064 wt% Ce-doped samples(as the optimum content of cerium in the alloy). Thus, the nickel-based alloy becomes less sensitive to the pitting by addition of cerium. The corrosion penetration depth reaches about 244 mm after 16 h of electrolysis in the un-doped sample, while was approximately 103 mm for the 0.0064 wt% Ce-doped sample, which is an indication that the corrosion penetration depth decreases by adding small amounts of Ce.

异种铝合金摩擦塞补焊接头微观组织及性能

采用2A14-T6铝合金圆锥塞棒和10 mm厚2219-T87铝合金板材进行异种铝合金摩擦圆锥塞焊工艺试验。对异种铝合金摩擦锥塞焊接头的缺陷特征、微观组织、强化相分布、力学性能及拉伸断口形貌进行观察与测试。结果表明:在焊接转速为7 500 r/min,焊接压力为30 k N和35 k N时得到了无缺陷的摩擦塞焊接头;摩擦塞焊接头可分为塞棒区(Plug metal,PM)、塞棒焊缝热力影响区(Plug thermo-mechanically affected zone,PTMAZ)、摩擦界面区(Friction interface zone,FIZ)、热力影响区(Thermo-mechanically affected zone,TMAZ)、热影响区(Heat affected zone,HAZ)和母材区(Base metal,BM)六部分;硬度测试结果显示,母材区硬度最高,塞棒区和塞棒焊缝热力影响区硬度略低于母材,热力影响区和热影响区最低。摩擦塞焊接头的抗拉强度最高可达312 MPa,伸长率可达4.1%;接头在下表面HAZ与TMAZ的交界处起裂,自下表面向上表面扩展,经过TMAZ,最终在上表面的PTMAZ断裂,断口呈韧窝形貌。

塞棒材料对铝合金摩擦塞补焊接头组织及拉伸断裂行为的影响

分别采用2A14-T6和2219-T87铝合金塞棒对6mm厚2219-T87铝合金板进行摩擦塞补焊实验,利用数字图像相关方法观测塞棒材料对拉伸过程中接头变形及断裂行为的影响,同时对两种接头的微观组织、显微硬度及拉伸断口进行观察与测试。结果表明:两种接头的组织特征相似,但2A14-T6接头的塞棒热力影响区发生部分再结晶的区域比2219-T87接头宽;塞棒材料对接头抗拉强度影响不大,但对伸长率影响显著,2219-T87接头抗拉强度可达346.2MPa,伸长率为5.76%;2A14-T6接头的抗拉强度可达351.2MPa,伸长率为3.54%;2219-T87接头的变形主要集中在软化的塞棒区和塞棒热力影响区,而2A14-T6接头的变形主要集中在软化的热力影响区和热影响区;再结晶区和接头软化区是整个接头的薄弱区,拉伸断口呈韧窝形貌。

7050铆钉静压铆接对铝合金板干涉量的研究

针对典型2A14-T6铝夹层,开展7050材质Φ2.5、Φ6两种规格铆钉采用静压铆接方式,铆钉钉杆在夹层不同位置处的尺寸变化量及与夹层干涉量的测量,得出尺寸变化量、干涉量的差异及规律。结果表明,变化量及干涉量从铆钉钉头向镦头部位过渡,逐渐变大。