重型运载火箭燃料贮箱FSW核心区温度监测

重型运载火箭燃料贮箱目前通常采用2219-T8高强铝合金,贮箱壁厚高达18 mm,采用搅拌摩擦焊(friction stir welding,FSW)工艺实现筒段纵缝和环缝焊装,FSW核心区极值温度直接影响焊接质量,但由于搅拌头旋转、轴肩遮挡等原因导致FSW核心区温度获取困难.文中提出了一种FSW核心区极值温度在位表征方法,首先,基于Deform-3D建立了18 mm厚2219-T8铝合金的FSW温度场仿真模型,实现了18 mm厚2219-T8铝合金平板和环焊温度场表征;然后,基于温度场仿真模型,提取焊件表面特征点温度与核心区极值温度的数据集,采用支持向量回归机算法(support vector regression,SVR)建立FSW核心区极值温度预测模型;最后,红外热像仪实时测得焊件表面特征点温度,结合核心区极值温度预测模型,实现贮箱FSW核心区极值温度监测.试验结果表明,FSW核心区峰值温度监测相对误差<7.22%,核心区最低温度相对误差<9.54%,证实了FSW核心区极值温度监测方法的有效性.

Review on friction stir welding of magnesium alloys

Friction Stir Welding(FSW)is considered to be the most significant development in metal joining in last two decades.FSW has many advantages when welding magnesium or lightweight alloys.The Friction stir welding of magnesium alloy has many potential applications in major industries i.e.land transportation,aerospace,railway,shipbuilding and marine,construction,and many other industrial applications.Even magnesium alloys have been used in industrial equipment of nuclear energy as magnesium alloys have low tendency to absorb neutrons,sufficient resistance to carbon dioxide and excellent thermal conductivity.Recently,the research and development in FSW field and associated technologies have been developing rapidly worldwide.In this review article,the basic principle of friction stir welding and several aspects of friction stir welded magnesium alloys have been described.The current state of friction stir welding of magnesium alloys is summarized.In spite of this,much remains to be learned about the process and opportunities for further research are identified.

Investigation of microstructure and mechanical properties of friction stir welded AZ61 magnesium alloy joint

Increasing global demands for energy conservation and environmental protection led to the replacement of heavy components with lighter alloys.As magnesium alloys are believed to be unique candidates for lightweight applications and friction stir welding(FSW)is capable of joining magnesium alloys,in the current work,FSW joint of AZ61 Mg alloy has been fabricated.Microstructure and mechanical properties of the joints were evaluated.The elongated grains of the base metal were recrystallized in the stir zone and in transition zone during friction stir welding.The formation of finer grains in the stir zone of the joint is responsible for increase the hardness of the stir zone.The microhardness of base metal is higher than that of thermo-mechanically affected zone but lower than that of stir zone.The tensile strength of the weld was about 82%of the as-received base metal.The joint failed in ductile mode.This ductile failure of joint was due to the uniform deformation of material.

Influence of tool rotation speeds on mechanical and morphological properties of friction stir processed nano hybrid composite of MWCNT-Graphene-AZ31 magnesium

The ever-increasing demand for light weighted hard materials for transportation industries encouraged researchers to develop composites with excellent mechanical properties which can transform it into more economical and eco-friendly.Reinforcing the metals with carbonaceous nanomaterials are progressively in focus due to their excellent capability to inculcate and tailor the properties of MMCs.In the present research,a hybrid nanocomposite of MWCNT-Graphene-AZ31 Mg alloy has been developed by using variable tool rotation speeds with friction stir processing(FSP).Optimized reinforcement ratio of 1.6%vol.MWCNT and 0.3%vol.of graphene have been used with variable tool rotation speeds,whereas other processing parameters are kept constant.The developed specimens were investigated using standard testing equipment for evaluating and comparing the mechanical properties on the basis of the microstructure of the processing regions and their morphological analysis,according to the ASTM standards.The obtained results revealed an improvement of 19.72%in microhardness and 77.5% of compressive strength in comparison with the base metal AZ 31 Magnesium alloy,with a tool rotational speed of 1400rpm.The values of tensile stress and percentage area reduction were recorded as less than that of the base metal matrix,but an increasing trend has been observed in the values of both with the improvement on rotational speeds of the tool.The effectual strengthening mechanisms are analyzed on the bases of SEM images and observed that discussed and found that grain refinement strengthening is the major contributor to the strength of the nanocomposite.

7075铝合金搅拌摩擦连接性能分析

采用单道对接连接的形式对7075铝合金进行搅拌摩擦连接试验,研究了不同参数下的微观组织和性能。结果表明:连接区中心与前进侧热机影响区分界线较为明显,与后退侧的分界线不明显。固定旋转速度为1000 r/min,随着进给速度从100 mm/min增大到300 mm/min,连接区抗拉强度先增大后减小,当进给速度为200 mm/min时,抗拉强度最高,达到了487.3 MPa,是母材的89.4%,当进给速度为300 mm/min时,抗拉强度较低,但也达到了母材的78.8%。连接区横截面维氏硬度呈“W”形分布,连接区中心硬度高于热影响区硬度,但低于母材硬度。各试样的磨损机理为黏着磨损和磨粒磨损,其中试样2的摩擦系数与磨损量均为最小,耐磨性最高。

Optimum condition by mechanical characteristic evaluation in friction stir welding for 5083-O Al alloy

The mechanical characteristies for friction stir welding (FSW) of 5083-O Al alloy were evaluated. The results show that in FSW at 800 r/min and 124 mm/min, a weld defect is observed at the start point. However, the button shape at the end point is good and the stir zone has a soft appearance. At 267 mm/min, a void occurs at the button. A slight weld defect and rough stir zone are seen both at the start and end points at 342 mm/min. Moreover, at the bottom, a tunnel-type void is observed from an early stage to the end point, and at 1 800 r/min, a weld defect can be found from an early stage to the end point. These defects are rough with imperfect joining due to excessive rotation speed and high physical force. Weld fractures relative to rotational and travel speeds are observed at the stir zone. The optimum FSW conditions are a welding speed of 124 mm/min and a rotational speed of 800 r/min.

潮间带临时便道袋包砂施工效率提升技术研究

本研究针对厦门机场吹填工程潮间带临时便道袋包砂施工工艺,开展了袋体缝制和备砂工艺优化的研究。研究表明,袋体缝制升级为3道同步缝制,可在保证袋体质量的基础上,显著提升袋体缝制效率;左右翻砂优化为前后翻砂工艺后,可显著降低施工过程各机械设备的干扰,提升备砂效率。基于此,所形成的袋包砂优化施工工艺,可显著提升施工效率,降低施工成本,对后续的潮间带袋包砂施工具有重要的指导意义。

Influence of tool pin profile on microstructure and corrosion behaviour of AA2219 Al-Cu alloy friction stir weld nuggets

To overcome the problems of fusion welding of aluminium alloys, the friction stir welding(FSW) is recognized as an alternative joining method to improve the mechanical and corrosion properties. Tool profile is one of the important variables which affect the performance of the FS weld. In the present work, the effect of tool profile on the weld nugget microstructure and pitting corrosion of AA2219 aluminium-copper alloy was studied. FSW of AA2219 alloy was carried out using five profiles, namely conical, square, triangle, pentagon and hexagon. The temperature measurements were made in the region adjacent to the rotating pin. It was observed that the peak temperature is more in hexagonal tool pin compared to the welds produced with other tool pin profiles. It is observed that the extensive deformation experienced at the nugget zone and the evolved microstructure strongly influences the hardness and corrosion properties of the joint during FSW. It was found that the microstructure changes like grain size, misorientation and precipitate dissolution during FSW influence the hardness and corrosion behaviour. Pitting corrosion resistance of friction stir welds of AA2219 was found to be better for hexagon profile tool compared to other profiles, which was attributed to material flow and strengthening precipitate morphology in nugget zone. Higher amount of heat generation in FS welds made with hexagonal profile tool may be the reason for greater dissolution of strengthening precipitates in nugget zone.

MICROSTRUCTURAL STUDIES OF FRICTION STIR WELDED AZ31 MAGNESIUM ALLOY

Friction stir welding achieves the weld in solid phase by locally introducing frictional heating and plastic flow arising from rotation of the welding tool, which results in changes in the local microstructure of magnesium alloy. The purpose in the paper is to study the microstructures of friction stir welded AZ31 magnesium alloy. Residual microstructures, including dynamic re-crystallization zone and nugget structures have been systematically investigated utilizing optical microscopy (OM), scanning electric microscopy (SEM), transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and micro-hardness. AZ31 magnesium alloy has been successfully friction stir welded and exhibits the variations of microstructure including dynamically recrystallized, equaxied grains in the weld nugget. Residual hardness in the nugget was found slightly lower than the parent but not too obvious.

Tool-workpiece interaction and shear layer flow during friction stir welding of aluminium alloys

Material flow phenomena during friction stir welding(FSW) and the forming mechanism of "onion rings" are complicated and currently not fully understood. In the present FSW study aluminium alloys 5083 and A356,with the latter more readily welded than the former,were used. The experiments were conducted to obtain samples of tool and workpiece "frozen" together during FSW for analysis. Two deposition modes for forming the weld nugget zone were observed,one for each alloy with the present FSW parameters. The first is the deposition of shear layers forming the "onion rings" in 5083 alloy nugget. The tool-workpiece interaction leading to the layer thickness being equal to the ratio of welding speed and tool rotation speed is suggested. The second mode is the combination of depositing the rotational shear material in the lower part on the advancing side and the drag flow of material from the retreating site forming the rest of the A356 nugget. The latter mode resulted in the absence of a clear ring structure.

Comparison of 2A12 aluminium alloy joint by ultrasonic assisted friction stir welding and friction stir welding

Ultrasonic assisted friction stir welding （UAFSW） is a recent modification of conventional friction stir welding, which adds ultrasonic energy directly into the friction stir welding area by the pin. In this study, 2A12 aluminum alloy was welded by this process and conventional, respectively. The tensile tests, microstructure and fracture surface of FSW joint and UAFSW joint were analyzed. The research results show that the surface forming texture of ultrasonic assisted friction stir welding joint, compared with conventional, is finer and more uniform, showing metallic matte color. The grains are much finer in weld nugget zone, thermo-mechanically affected zone and heat-affected zone; S-phase particles size is much smaller and distribution is more homogeneous in the matrix. The tensile strength of UAFSW joint is 94. 13% of base metal, and the elongation is 11.77%. The tensile strength of FSW joint is 83.15% of base metal, and the elongation is 8.81%. The tests results reveal that ultrasonic vibration can improve the tensile strength and the elongation of welded joints.

2A12/AZ31B异质合金超声振动辅助搅拌摩擦焊核区晶粒组织

开展了2A12/AZ31B异种材料搅拌摩擦焊(FSW)和超声振动辅助搅拌摩擦焊(UVaFSW)的对比工艺实验,对焊核区不同部位的晶粒组织加以表征,分析超声振动对晶粒组织演变的影响。结果表明:相比于母材,焊核区2A12铝侧与AZ31B镁侧的晶粒尺寸都得到了明显的细化。2A12铝侧焊核区晶粒动态再结晶的方式为连续动态再结晶(CDRX)与几何动态再结晶(GDRX)机制的共同作用。AZ31B镁侧焊核区晶粒动态再结晶的方式为CDRX,GDRX和非连续动态再结晶(DDRX)机制的共同作用。施加超声振动能够促进晶粒的再结晶程度,尤其是在铝侧的中下部和镁侧的底部。织构演变结果表明:施加超声振动,铝侧焊核区材料的应变增加,说明超声振动能够促进焊核区的材料流动;镁侧不同区域的织构强度都有所降低,这是因为施加超声时镁合金晶粒发生了更加完全的再结晶行为,从而减弱了晶粒的取向性。

基于CFD数值模拟的高固厌氧消化搅拌设备优化分析

高固厌氧消化(High Solid Anaerobic Digestion,HSAD)相比传统厌氧消化存在混合效果差、能量转换效率低等缺点,而机械搅拌不仅促进消化,同时有效解决高固厌氧消化受高黏度非牛顿流体限制的问题。本研究基于气液两相流混合模型,借助计算流体力学(Computational Fluid Dynamics,CFD)对3类高固厌氧反应器的流场进行数值模拟,探寻最佳工况。研究表明,螺带搅拌桨在高黏度流体混合中具有优越性;同时根据不同转速下反应器内的流场与死区分析,得到3类搅拌反应器混合特征,为实际高固厌氧消化搅拌机械的选用提供了理论指导。

电磁搅拌电源死区补偿系统设计与实现

电磁搅拌电源输出低失真电流波形是电磁搅拌器负载产生标准的旋转磁场并能长期可靠运行的重要保证。电磁搅拌专用电压型逆变器由于死区的存在不可避免地会对输出电流波形造成影响。针对电磁搅拌专用电压型逆变器死区的影响,对电压逆变器所必需的死区时间和其特性效应进行了分析。根据死区效应分析,结合电磁搅拌负载系统自身属重感性负载,设计了一种实时调整每个载波周期中的实际IGBT导通时间的补偿方法,达到消除死区效应影响的目的,并且通过试验验证了所采用方法可以有效改善输出电流的波形畸变,降低输入至电磁搅拌器负载中电流的谐波含量。

复合搅拌摩擦点焊旋转半径对接头组织和性能的影响

对2 mm 2A12-T4铝合金薄板采用复合搅拌摩擦点焊进行焊接,测试不同旋转半径下的复合搅拌摩擦点焊接头的抗剪力,并观察和分析复合搅拌摩擦点焊接头在拉伸时的断裂途径及微观组织.结果表明:当其他参数不变时,复合搅拌摩擦点焊接头抗剪力和断裂途径随旋转半径和塑性环形貌的不同而变化;在旋转半径为1.2 mm时,接头的抗剪力达到最大值为2 948 N;随着旋转半径增大,热输入增大,接头塑性环区增宽并致密,使接头抗剪力增大,但过大的旋转半径则因热输入过大,使塑性环区致密度降低,并出现孔洞等缺陷,接头抗剪力降低;焊点塑性环区晶粒最细小,组织致密,硬度最高.

铝合金无针搅拌摩擦焊接技术改进研究

针对薄板轻合金焊接难的问题,对无针搅拌头进行了改进,并对6061-T6铝合金板料进行了搅拌摩擦焊接。利用宏观形貌分析、拉伸试验等方法,研究了无针搅拌摩擦焊缝的强度。结果表明:在搅拌头内嵌入与被焊材料相同的棒料,可增大搅拌头与工件间的摩擦系数和黏附性,从而增大焊缝搅拌区厚度。嵌入搅拌头中的棒料直径越大,焊缝强度越高。嵌入搅拌头棒料直径增大为10 mm时,焊缝抗拉强度最大,约为180 MPa,达到母材强度的62%。

转炉局域搅拌和混匀效果的水模型实验

为研究转炉的局域搅拌和混匀效果,以55 t转炉为原型,建立转炉水模型,在不同喷吹条件下,通过多点测量的方式,对转炉进行水模拟实验。结果表明:纯底吹条件下,底部中心处的混匀时间较短;顶吹条件下,底部中心处搅拌最弱;顶底复吹条件下,随着枪位的升高,熔池内4个测量点的混匀时间均先变小后增大,并找到平均混匀时间最短的底吹方式,在此底吹布置方式下的枪位为0.16 m时,侧壁面的上部和下部以及环流中心附近混匀效果较好,枪位为0.20 m时,底部中心处的混匀时间最短。进一步比较底吹对称布置和非对称布置下的搅拌和混匀效果可知,底吹喷嘴的非对称且集中布置更有利于改善转炉内流场,减少搅拌弱区。

搅拌摩擦焊焊接5083铝合金板材焊核区的晶体取向

采用搅拌摩擦焊焊接了5083铝合金板材,借助电子背散射衍射技术和取向成像分析软件,对比性地分析了母材和焊核区的晶粒形貌、取向差分布、织构组分及取向分布函数,分析了焊核区晶体取向的变化.结果表明,在热—力作用下,焊核区发生动态再结晶,显示等轴晶粒形貌,平均晶粒尺寸约为15.8μm,同时大角度晶界比例明显增加.母材的黄铜织构B{011}<211>和S织构{123}<634>的比例分别达到30.6%和13.6%以上;搅拌摩擦焊后,焊核区的B织构和S织构的比例分别降至4%和1.8%,原位再结晶形成的R{124}<211>织构组分约为7.7%,焊核区其它常见面心立方金属织构组分的比例均低于8%,意味着焊核区由强取向组织转变为弱取向组织.

电磁搅拌提高铸坯等轴晶比率的数值模拟

采用单侧线性电磁搅拌技术进行了铸坯的静态浇铸实验 ,并对电磁搅拌过程中的电磁场和流场进行了数值模拟 ,确定了实验条件下获得全等轴晶铸坯的电磁搅拌参数·结果表明 ,在本实验条件下 ,当最大电磁搅拌强度为 1414AHz ,钢液中的最大电磁力及最大流动速度分别达到 6 386N/m3 和 0 2 2m/s时 ,获得了等轴晶比率几乎为 10 0 %的铸坯·

连铸板坯二冷区辊式电磁搅拌的磁场数值模拟

通过ANSYS有限元分析软件,在电流频率为6 Hz、电流强度变化的情况下,对连铸板坯二冷区电磁搅拌进行了数值模拟。分析了电流强度为400 A、电流频率为6 Hz时,铸坯内部的磁感应强度和电磁力的变化规律。结果表明,铸坯中心的磁感应强度随电流强度的增大而增大;铸坯中心的电磁力在一个周期的不同时刻向同一个方向移动,并在该力的作用下完成对钢液的搅拌。