预拉伸控制铝合金焊接变形

在预拉伸应力作用下,焊接了厚度为4mm的5A05铝合金试板,通过焊接试板挠曲变形量的测定,探讨了预加拉应力对铝合金焊接变形的影响。试验结果表明,预拉伸焊接法可以有效减小铝合金薄板焊缝处的纵向挠曲变形量,在弹性应力范围内,随着预拉伸应力的增大,试板的焊接变形逐渐变小。初步分析认为,预拉伸应力扩大了高温下焊缝附近的塑性变形区,从而增强了冷却过程中该区域抗塑性拉应变的能力,减小了焊件的挠曲变形。

LPJ9.5系列焊接拉伸型爆破片起爆误差控制

LPJ9.5系列焊接拉伸型爆破片装置具有结构紧凑、起爆压力调节方便等优点,因而被大量应用于石油和天然气钻采设备上.本文着重论述LPJ9.5系列焊接拉伸型爆破片装置的结构特点、影响爆破片起爆精度的主要因素以及提高起爆精度的措施.实践表明:LPJ9.5系列焊接拉伸型爆破片的起爆误差及其控制对象主要在于膜片材料的物理性能和厚度、排放口径加工精度、下夹持环的孔口圆角半径尺寸以及焊接方法和焊接参数.

焊管焊接接头拉伸试验相关标准的讨论

焊管常用标准对焊缝接头拉伸试样是否去除焊缝余高要求不一。本文从焊接接头拉伸的实际意义出发,探讨了是否去除焊缝余高及断裂位置对试验结果的影响。不去除焊缝余高的情况,更偏重于焊缝结构的整体强度,而不是严格意义上的焊接接头的抗拉强度。为避免分歧及便于对比,西气东输二线管道工程技术条件中统一规定了焊接接头拉伸试验必须去除焊缝余高,且报告断裂位置。

激光冲击强化对不锈钢焊接接头拉伸性能的重要性分析

不锈钢材料具有较好的塑性与韧性,尤其是抗腐蚀性能较好,在石油、化工、航空、原子能等领域具有广泛的运用。不锈钢焊接接头可利用激光冲击进行强化处理,通过前后两次的激光冲击后对焊接接头拉伸性能、显微硬度、表面残余应力等进行比较。实验结果表明,在二次激光冲击强化后焊接接头其显微硬度、拉伸强度等均有较大的提升,且焊接断裂区域转移由热影响区转移到机体,如此的有效提升了不锈钢焊接接头的拉伸性。其中焊接残余应力的消除是激光冲击强化提升焊接接头拉伸性能的主要因素。

现场钢轨拉伸锁定闪光焊技术研究

现场钢轨拉伸锁定焊接技术通过改变原有闪光焊过程控制方式和现场施工组织方案,将闪光焊过程分为加热和顶锻2个阶段分控,加热阶段长钢轨处于自由状态,顶锻阶段通过拉伸钢轨实现顶锻的同时恢复线路锁定轨温,采用闪光焊和感应热处理一体机,在焊接和焊后热处理过程中实现全程保压,焊接质量稳定可靠。闪光焊拉伸线上锁定焊接工艺可同时解决目前线路施工中的合龙口焊接及线路恢复锁定轨温的难题,实现岔区、胶结绝缘外无缝线路全部可采用闪光焊完成的技术突破。

高速铁路现场钢轨插入闪光焊接技术研究

随着闪光焊轨机或焊轨车的大范围普及,高速铁路新建和既有线区间无缝线路基本都采用闪光焊接,近几年现场闪光焊开始大范围应用于线上局部换轨的插入焊接。研究适用于高速铁路现场钢轨插入焊接技术,对于解决一些因服役或偶发性外因导致钢轨或焊接接头的损伤修复十分重要。在保证焊接接头质量的前提下,满足插入焊合龙口接头的焊接和锁定轨温恢复两方面需求是技术研究的关键难点。通过分析高速铁路现场插入闪光焊需求及关键技术,制定了适应现场作业需求的焊接装备、作业模式和现场施工组织,为高速铁路现场插入闪光焊接提供了新的技术方案。

纯镍Ni200等离子焊接工艺参数正交试验优化设计

以6mm厚纯镍Ni200为试验材料，采用正交试验设计方法科学地安排试验过程，研究焊接工艺参数与接头抗拉强度之间的关系。研究发现，焊接电流对焊接接头抗拉强度影响最显著，离子气体流量和焊接速度影响次之。通过正交试验设计确定最优工艺规范为：焊接电流200A，焊接速度180mm／min，离子气体流量3L／min，保护气体流量20～221Mmin。最优工艺规范下焊缝成形良好，接头抗拉强度明显升高。试验表明，等离子焊接中厚镍板是一种理想的焊接方法。

Quasi-static and dynamic tensile behaviors in electron beam welded Ti-6Al-4V alloy

The quasi-static and dynamic tensile behaviors in electron beam welded（EBW） Ti-6Al-4V alloy were investigated at strain rates of 10-3 and 103 s-1,respectively,by materials test system（MTS） and reconstructive Hopkinson bars apparatus.The microstructures of the base metal（BM） and the welded metal（WM） were observed with optical microscope.The fracture characteristics of the BM and WM were characterized with scanning electronic microscope.In Ti-6Al-4V alloy joint,the flow stress of WM is higher than that of BM,while the fracture strain of WM is less than that of BM at strain rates of 103 and 10-3 s-1,respectively.The fracture strain of WM has apparent improvement when the strain rate rises from 10-3 to 103 s-1,while the fracture strain of BM almost has no change.At the same time,the fracture mode of WM alters from brittle to ductile fracture,which causes improvement of the fracture strain of WM.

Mechanical properties and wear resistance of aluminum composite welded by electron beam

The welding property of TiB2/ZL101 composite was investigated using electron beam（EB） welding experimental system with a function generator.The fine defect-free welding seam was obtained under proper processing parameters and scanning rate.The reinforcement particles TiB2 distributed homogeneously in welding seam without any segregation.The tensile results show that fracture occurs at the base metal and elastic modulus increases compared with base metal.Wear resistance of welding seam is improved greatly compared with base metal.The results show that the TiB2/ZL101 composite can be successfully welded by EB technology.

Comparison of explosive welding of pure titanium/SUS 304 austenitic stainless steel and pure titanium/SUS 821L1 duplex stainless steel

Pure commercial titanium was welded with two types of stainless steel,namely SUS 304 austenitic stainless steel and SUS 821L1 duplex stainless steel.The wavy interface of SUS 821L1 was smaller than that of SUS 304.The vortex zone was observed from both longitudinal and transverse directions,and its composition was analyzed.The interface of Ti/SUS 821L11 was able to bear 401−431 MPa shear load while that of Ti/SUS 304 could withstand 352−387 MPa.The weldability window was used to analyze experimental phenomenon.Furthermore,the smoothed particle hydrodynamics(SPH)numerical simulation method was used to simulate the wavy interface.The trend of wavelength and amplitude change with strength and the stand-offs was consistent with the experimental results.

Effect of welding processes on AA2219 aluminium alloy joint properties

AA2219 aluminium alloy square butt joints without filler metal addition were fabricated using gas tungsten arc welding （GTAW）, electron beam welding （EBW） and friction stir welding （FSW） processes. The effects of three welding processes on the tensile, fatigue and corrosion behaviour were studied. Microstructure analysis was carried out using optical and electron microscopes. The results show that the FSW joints exhibit superior tensile and fatigue properties compared to EBW and GTAW joints. It is also found that the friction stir welds show lower corrosion resistance than EB and GTA welds. This is mainly due to the presence of finer grains and uniform distribution of strengthening precipitates in the weld metal of FSW joints.

Establishing empirical relationships to predict grain size and tensile strength of friction stir welded AA 6061-T6 aluminium alloy joints

AA 6061-T6 aluminium alloy(Al-Mg-Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring a high specific strength and good corrosion resistance.Compared with the fusion welding processes that are routinely used for joining structural aluminium alloys,friction stir welding(FSW) process is an emerging solid state joining process in which the material welded does not melt and recast.Joint strength is influenced by the grain size and tensile strength of the weld nugget region.Hence,an attempt was made to develop empirical relationships to predict grain size and tensile strength of friction stir welded AA 6061-T6 aluminium alloy joints.The empirical relationships are developed by response surface methodology(RSM) incorporating FSW tool and process parameters.A linear regression relationship was also established between grain size and tensile strength of the weld nugget of FSW joints.

Effects of laser beam welding parameters on mechanical properties and microstructure of AZ31B magnesium alloy

The effects of laser beam welding process parameters such as laser power,welding speed and focal position on mechanical properties and microstructure of AZ31B magnesium alloy were studied.Nine joints were fabricated using different levels of laser power,welding speed and focal position.Tensile properties of the welded joints were evaluated and correlated with the weld zone microstructure and hardness.It is found that the joints fabricated using a laser power of 2 500 W,welding speed of 5.5 m/min and focal position of-1.5 mm yield superior tensile properties compared with the other joints.The formation of very fine grains in weld region,higher fusion zone hardness and uniformly distributed finer precipitates are the main reasons for superior tensile properties of these joints.

Corrosion behavior and mechanical properties of cold metal transfer welded dissimilar AA7075-AA5754 alloys

Cold metal transfer(CMT) welding is a brand-new arc welding technique which shows adequate results for welding of thin sheets and dissimilar materials. Corrosion behavior of dissimilar aluminum joints should be determined in terms of predicting the effect of welding process on the possible failures in their constructions caused by corrosive agents. The present study investigates the effect of heat input on mechanical properties and corrosion rate of AA5754-AA7075 joints welded by CMT using ER5356 filler wire. Pore formation was observed not only in the weld metal but also in the partially melted zone of AA7075 base metal due to the vaporization of zinc. Increased heat input caused over aging and zinc vaporization in AA7075 base metal, and grain coarsening in AA5754 base metal consequently decreased the tensile strength. The average tensile strength of AA7075-AA5754 joints varies between 235 and 240 MPa. The ductile fracture occurred at the AA5754 base metal side in all samples. Pitting was observed as the dominant corrosion mechanism. Corrosion resistance tended to increase with increasing heat input. Heat input values between 95 and 110 J/mm are recommended for the optimization of corrosion resistance and strength.

Microstructural zones and tensile characteristics of friction stir welded joint of TC4 titanium alloy

TC4 titanium alloy was friction stir welded using a W-Re pin tool,and the defect-free weld was produced with proper welding parameters.The joint consists of stir zone,heat affected zone and base material.The stir zone is characterized by equiaxed dynamically recrystallized α phases and transformed β phases with fine α+β lamellar microstructure.The microstructure of the heat-affected zone is similar to that of the base material,but there is an increase in the volume fraction of β.Transverse tensile strength of the joint is 92% that of the base material,and the joint is fractured in the stir zone and the fracture surface possesses typical plastic fracture characteristics.The stir zone is the weakest part of the joint,through which the tensile characteristics of the TC4 joint can be explained.

Effect of welding speed on microstructural characteristics and tensile properties of GTA welded AZ31B magnesium alloy

The effect of welding speed on tensile and microstructural characteristics of pulsed current gas tungsten arc welded（PCGTAW） AZ31 B magnesium alloy joints was studied. Five joints were fabricated using different levels of welding speeds（105-145 mm/min）. It was found that the joints fabricated using a welding speed of 135 mm/min yielded superior tensile properties compared to other joints. The formation of fine grains and uniformly distributed precipitates in the fusion zone are the main reasons for the superior tensile properties of these joints.

Mechanical properties of underwater friction stir welded 2219 aluminum alloy

Underwater friction stir welding of 2219 aluminum alloy was carried out in order to further improve the joint performances by varying welding temperature history.The results indicated that the tensile strength of the joint can be improved from 324 MPa by external water cooling action in normal to 341 MPa.However,the plasticity of the joint is deteriorated.The underwater joint tends to fracture at the interface between the weld nugget zone and the thermal mechanically affected zone on the advancing side during tensile test,which is significantly different from the normal joint.

Study on Interfacial Bonding State of Ag-Cu in Cold Pressure Welding

The interfacial bonding of Ag-Cu (they are limited soluble) formed by the technology of cold pressure welding was discussed from the point of metallurgic view in this paper. Meanwhile, tensile test and microscopic test were adopted for studying the state of interfacial bonding, suggesting that the joint of Ag-Cu has not only strong welding joint but also atomic diffusion on the interface. For Ag-Cu, the interaction of dislocation caused by plastic deformation will cause the strain and the vibration of microconstructer defects, accompanied by emitting energy. The energy increases the atomic action and the amplitude of atomic vibration, and the result is that the atom can diffuse to several lattice parameters deep from interface to inner metals. Therefore, under the condition of chemical potential gradient, the special technique, cold pressure welding rather than basic requirements of diffusion should be taken into account. During the cold pressure welding, plastic deformation plays an important role for it causes the metals′ displacement, crystal defects, further activates the surface atoms. Finally, the fracture of atomic bonding leads to the atomic exchange and diffusion between the new metals′ surfaces.In other words the metals Ag,Cu can achieve solidate bonding by cold pressure welding accompanied by the atomic diffusion. Moreover, theoretical analysis and calculation on the basis of thermodynamics, crystallogy, so- lid physics,etc, have been applied to calculate the amount of atomic diffusion, which has further proved the testing results that joint Ag-Cu has strong bonding strength through the mechanism of atomic diffusion.

Optimization of process parameters to maximize ultimate tensile strength of friction stir welded dissimilar aluminum alloys using response surface methodology

Aluminium alloys generally present low weldability by traditional fusion welding process. Development of the friction stir welding （FSW） has provided an alternative improved way of producing aluminium joints in a faster and reliable manner. The quality of a weld joint is stalwartly influenced by process parameter used during welding. An approach to develop a mathematical model was studied for predicting and optimizing the process parameters of dissimilar aluminum alloy （AA6351 T6-AA5083 Hlll）joints by incorporating the FSW process parameters such as tool pin profile, tool rotational speed welding speed and axial force. The effects of the FSW process parameters on the ultimate tensile strength （UTS） of friction welded dissimilar joints were discussed. Optimization was carried out to maximize the UTS using response surface methodology （RSM） and the identified optimum FSW welding parameters were reported.

Prediction and optimization of process parameter of friction stir welded AA5083-H111 aluminum alloy using response surface methodology

A systematic approach was presented to develop the empirical model for predicting the ultimate tensile strength of AA5083-H111 aluminum alloy which is widely used in ship building industry by incorporating friction stir welding(FSW) process parameters such as tool rotational speed,welding speed,and axial force.FSW was carried out considering three-factor five-level central composite rotatable design with full replications technique.Response surface methodology(RSM) was applied to developing linear regression model for establishing the relationship between the FSW process parameters and ultimate tensile strength.Analysis of variance(ANOVA) technique was used to check the adequacy of the developed model.The FSW process parameters were also optimized using response surface methodology(RSM) to maximize the ultimate tensile strength.The joint welded at a tool rotational speed of 1 000 r/min,a welding speed of 69 mm/min and an axial force of 1.33 t exhibits higher tensile strength compared with other joints.