Ni/Al/Zn钎料层对AZ31/2024异种金属钎焊接头组织及性能的影响

采用Ni/Al/Zn复合钎料层对AZ31和2024合金实现了大气环境下、无钎剂的超声辅助瞬间液相扩散连接(U-TLP),研究采用Ni层、Ni/Zn层、Zn/Ni/Zn层及Al/Zn/Ni/Zn层时钎缝的微观组织及接头的力学性能,分析Ni箔、Al箔及Zn箔在U-TLP过程中的作用。结果表明:通过调整Ni/Al/Zn复合钎料层的组合形式,可以实现对钎缝微观组织的调控及力学性能的改善,采用Al/Zn/Ni/Zn复合钎料层时钎缝剪切强度达到最高值(95.3MPa)。Ni箔起到了"物理屏障"的作用,阻碍了Mg-Al金属间化合物(IMCs)的形成,但是由于铝合金一侧钎缝仅由Al_(3)Ni组成,接头剪切强度仅为21.2 MPa。Zn箔的添加促进铝母材溶解,增加Al_(3)Ni的数量并形成Zn-Al共晶,提高2024合金一侧的连接强度。Al箔的填入降低AZ31合金的溶蚀,并在镁合金侧形成MgZn_(2)、MgZn和含有Mg_(2)Ni、Al_(3)Ni、AlMg_(4)Zn_(11)和NiZn_(8)的混合IMCs层的组织,提高AZ31合金与Ni箔的连接。

C/C复合材料钎焊接头应力场的有限元分析

异种材料钎焊接头中的残余应力是接头连接质量低的主要原因之一。本工作基于热-弹-塑性理论,以Abaqus有限元软件为平台,采用数值模拟计算的方法,研究C/C-C/C、C/C-TiAl同种及异种材料钎焊接头残余应力状态,揭示应力分布对接头连接性能的影响。结果表明:不同钎焊接头中,等效应力大小和分布状态不同。同种材料接头中应力集中分布在钎缝和C/C复合材料钎焊面棱角处,从外向内逐渐减小;异种材料接头中,应力集中在靠近钎缝区域的C/C复合材料上,从内向外逐渐减小。影响接头性能的应力主要为钎缝轴向正应力和垂直于轴向的切应力。同种材料接头中残余应力较小,C/C复合材料受轴向拉应力几乎为零,影响其连接性能的主要是切应力。异种材料接头中残余应力较高,C/C复合材料中最大轴向拉应力分布在棱角位置,最大切应力分布在钎焊面内部。

Time-dependent effects in transient liquid phase bonding of 304L and Cp-Ti using an Ag-Cu interlayer

One of the challenges for bimetal manufacturing is the joining process.Hence,transient liquid phase(TLP)bonding was performed between 304L stainless steel and Cp-Ti using an Ag-Cu interlayer with a thickness of 75μm for bonding time of 20,40,60,and 90 min.The bonding temperature of 860℃ was considered,which is under the β transus temperature of Cp-Ti.During TLP bonding,various intermetallic compounds(IMCs),including Ti_(5)Cr_(7)Fe_(17),(Cr,Fe)_(2)Ti,Ti(Cu,Fe),Ti_(2)(Cu,Ag),and Ti_(2)Cu from 304L toward Cp-Ti formed in the joint.Also,on the one side,with the increase in time,further diffusion of elements decreases the blocky IMCs such as Ti_(5)Cr_(7)Fe_(17),(Cr,Fe)_(2)Ti,Ti(Cu,Fe)in the 304L diffusion-affected zone(DAZ)and reaction zone,and on the other side,Ti_(2)(Cu,Ag)IMC transformed into fine morphology toward Cp-Ti DAZ.The microhardness test also demonstrated that the(Cr,Fe)_(2)Ti+Ti_(5)Cr_(7)Fe_(17) IMCs in the DAZ on the side of 304L have a hardness value of HV 564,making it the hardest phase.The maximum and minimum shear strength values are equal to 78.84 and 29.0 MPa,respectively.The cleavage pattern dominated fracture surfaces due to the formation of brittle phases in dissimilar joints.

一种低温高强软钎料

设计了一种用于钎焊ZG16CrMnTi合金和LNG5磁钢的低温Cd基钎料。测试了不同成分钎料在ZG16CrMnTi及LNG5磁钢上的润湿性、接头抗拉强度、抗剪强度及抗冲击值,并对接头进行了微观分析。结果表明,在低温-50℃下,接头抗拉强度达280MPa以上。在200°C时,接头抗拉强度可达20MPa。接头中的ε’相（主要由Zn-Ag组成）在钎缝中起到强化作用。

Microstructure and mechanical properties of dissimilar pure copper/1350 aluminum alloy butt joints by friction stir welding

The dissimilar friction stir welding of pure copper/1350 aluminum alloy sheet with a thickness of 3 mm was investigated. Most of the rotating pin was inserted into the aluminum alloy side through a pin-off technique, and sound welds were obtained at a rotation speed of 1000 r/min and a welding speed of 80 mm/min. Complicated microstructure was formed in the nugget, in which vortex-like pattern and lamella structure could be found. No intermetallic compounds were found in the nugget. The hardness distribution indicates that the hardness at the copper side of the nugget is higher than that at the aluminum alloy side, and the hardness at the bottom of the nugget is generally higher than that in other regions. The ultimate tensile strength and elongation of the dissimilar welds are 152 MPa and 6.3%, respectively. The fracture surface observation shows that the dissimilar joints fail with a ductile-brittle mixed fracture mode durin~ tensile test.

Effect of joining temperature on microstructure and properties of diffusion bonded Mg/Al joints

The joining of AZ31B Mg alloy to 6061 Al alloy was investigated at different joining temperatures by vacuum diffusion bonding method. The microstructures of Mg/Al dissimilar joints were studied by means of optical microscopy （OM）, scanning electron microscopy （SEM） and energy dispersive X-ray （EDX）. The results show that the thickness of each layer in the diffusion zone increases with the increase of joining temperature, and the microstructure changes obviously. At joining temperature of 440 °C, the diffusion zone is composed of Mg2Al3 layer and Mg17Al12 layer. At joining temperatures of 460 and 480 °C, the diffusion zone is composed of Mg2Al3 layer, Mg17Al12 layer, eutectic layer of Mg17Al12 and Mg-based solid solution. The width of high-hardness zone in the joint increases with increasing joining temperature, and the micro-hardnesses at different locations in the diffusion zone are significantly different. The joining temperature of 440 °C offers the highest tensile strength of 37 MPa, and the corresponding joint exhibits brittle fracture at the intermetallic compound layer of Mg17Al12.

Electron beam welding of 304 stainless steel to QCr0.8 copper alloy with copper filler wire

Electron beam welding （EBW） of 304 stainless steel to QCr0.8 copper alloy with copper filler wire was carried out. Orthogonal experiment was performed to investigate the effects of process parameters on the tensile strength of the joints, and the process parameters were optimized. The optimum process parameters are as follows：beam current of 30 mA, welding speed of 100 mm/min, wire feed rate of 1 m/min and beam offset of-0.3 mm. The microstructures of the optimum joint were studied. The results indicate that the weld is mainly composed of dendriticαphase with little globularεphase, and copper inhomogeneity only occurs at the top of the fusion zone. In addition, a melted region without mixing exists near the weld junction of copper side. This region with a coarser grain size is the weakest section of the joints. It is found that the microhardness of the weld decreases with the increase of the copper content in solid solution. The highest tensile strength of the joint is 276 MPa.

Interface characteristic of friction stir welding lap joints of Ti/Al dissimilar alloys

Lap joints of TC1 Ti alloy and LF6 A1 alloy dissimilar materials were fabricated by friction stir welding and corresponding interface characteristics were investigated. Using the selected welding parameters, excellent surface appearance forms, but the interface macrograph for each lap joint cross-section is different. With the increase of welding speed or the decrease of tool rotation rate, the amount of Ti alloy particles stirred into the stir zone by the force of tool pin decreases continuously. Moreover, the failure loads of the lap joints also decrease with increasing welding speed and the largest value is achieved at welding speed of 60 mm/min and tool rotation rate of 1500 r/min, where the interracial zone can be divided into 3 kinds of layers. The microhardness of the lap joint shows an uneven distribution and the maximum hardness of HV 502 is found in the middle of the stir zone.

Influences of diffusion bonding process parameters on bond characteristics of Mg-Cu dissimilar joints

In many circumstances,dissimilar metals have to be bonded together and the resulting joint interfaces must typically sustain mechanical and/or electrical forces without failure,which is not possible by fusion welding processes.The melting points of magnesium(Mg)and copper(Cu)have a significant difference(nearly 400℃)and this may lead to a large difference in the microstructure and joint performance of Mg-Cu joints.However,diffusion bonding can be used to join these alloys without much difficulty.This work analyses the effect of parameters on diffusion layer thickness,hardness and strength of magnesium-copper dissimilar joints.The experiments were conducted using three-factor,five-level,central composite rotatable design matrix.Empirical relationships were developed to predict diffusion layer thickness,hardness and strength using response surface methodology.It is found that bonding temperature has predominant effect on bond characteristics.Joints fabricated at a bonding temperature of 450℃, bonding pressure of 12 MPa and bonding time of 30 min exhibited maximum shear strength and bonding strength of 66 and 81 MPa, respectively.

Corrosion behavior of dissimilar copper/brass joints welded by friction stir lap welding in alkaline solution

This study was done to evaluate the nugget zone(NZ)corrosion behavior of dissimilar copper/brass joints welded by friction stir lap welding(FSLW)in a solution of 0.015 mol/L borax(pH 9.3).To this end,dissimilar copper/brass plates were welded with two dissimilar heat inputs(low and high)during the welding procedure.The high and low heat inputs were conducted with 710 r/min,16 mm/min and 450 r/min,25 mm/min,respectively.Using open circuit potential(OCP)measurements,electrochemical impedance spectroscopy(EIS)and Tafel polarization tests,the electrochemical behavior of the specimens in borate buffer solution was assessed.With the help of scanning electron microscope(SEM),the morphology of welded specimen surfaces was examined after immersion in the test solution.According to the results,the NZ grain size and resistance improvement reduced due to the nugget zone corrosion with a decreased heat input.The results obtained from Tafel polarization and EIS indicated the improved corrosion behavior of the welded specimen NZ with a decrease in the heat input during the welding process unlike the copper and brass metals.Furthermore,an increased heat input during the welding process shows a reduction in the conditions for forming the passive films with higher protection behavior.

Microstructure and tensile properties of friction stir welded dissimilar AA6061-AA5086 aluminium alloy joints

The fusion welding of dissimilar heat treatable and non-heat treatable aluminium alloy faced many problems related to solidification. The difficulties can be overcome to achieve the combined beneficial properties of both aluminium alloys using friction stir welding(FSW). The microstructural features and tensile properties of friction stir welded(FSW) similar and dissimilar joints made of AA6061 and AA5086 aluminium alloys were investigated. The microstructures of various regions were observed and analyzed by means of optical and scanning electron microscopy. Microhardness was measured at various zones of the welded joints. The tensile properties of the joints were evaluated and correlated with the microstructural features and microhardness values. The dissimilar joint exhibits a maximum hardness of HV 115 and a joint efficiency of 56%. This was attributed to the defect free stir zone formation and grain size strengthening.

Preparation of bimetallic nano-composite by dissimilar friction stir welding of copper to aluminum alloy

Butt friction stir welding between pure copper and AA5754 alloy was carried out.Reinforcing SiC nanoparticles were utilized in friction stir welded(FSW)joints to decline the harmful effects of intermetallic compounds.Tensile tests,micro-hardness experiments,scanning electron microscopy and X-ray diffraction analysis were applied to studying the properties of welded joints.The joints with a travel speed of 50 mm/min and a rotation speed of 1000 r/min showed the best results.The presence of nano-sized SiC particles reduced the grain size of aluminum and copper in the stir zone(SZ)from 38.3 and 12.4μm to 12.9 and 5.1μm,respectively.The tensile strength of the joint in the presence of reinforcing SiC nano-particles was~240 MPa,which is~90%of that for the aluminum base.Furthermore,the highest microhardness of the weld zone was significantly increased from HV 160 to HV 320 upon the addition of SiC nano-particles.The results also showed that raising the heat generation in FSW joints increased the amount of Al_(4)Cu_(9) and Al_(2)Cu intermetallic compounds.

Microstructure and high-temperature mechanical properties of laser beam welded TC4/TA15 dissimilar titanium alloy joints

The microstructure evolution and high-temperature mechanical properties of laser beam welded TC4/TA15 dissimilar titanium alloy joints under different welding parameters were studied.The results show that the weld fusion zone of TC4/TA15 dissimilar welded joints consists of coarsenedβcolumnar crystals that contain mainly acicularα’martensite.The heat affected zone is composed of the initialαphase and the transformedβstructure,and the width of heat affected zone on the TA15 side is narrower than that on the TC4 side.With increasing temperature,the yield strength and ultimate tensile strength of the TC4/TA15 dissimilar welded joints decrease and the highest plastic deformation is obtained at 800°C.The tensile strength of the dissimilar joints with different welding parameters and base material satisfies the following relation(from high to low):TA15 base material>dissimilar joints>TC4 base material.The microhardness of a cross-section of the TC4/TA15 dissimilar joints reaches a maximum at the centre of the weld and is reduced globally after heat treatment,but the microhardness distribution is not changed.An elevated temperature tensile fracture of the dissimilar joints is located on the side of the TC4 base material.Necking occurs during the tensile tests and the fracture characteristics are typical when ductility is present in the material.

Microstructure and mechanical properties of TIG/A-TIG welded AZ61/ZK60 magnesium alloy joints

The dissimilar joints of AZ61 and ZK60 magnesium alloys were obtained by tungsten inert gas arc(TIG)welding and activating tungsten inert gas arc(A-TIG)welding processes.Microstructure characterization shows that,the fineα-Mg equiaxed dendrite crystals contained Mg17Al12 and MgZn2 particles in the fusion zone.The average size of theα-Mg grains in the fusion zone was refined to 19μm at welding current of 80 A,which resulted in the largest tensile strength of 207 MPa.The tensile strength and the width of the beam of the A-TIG welded AZ61/ZK60 joints showed strong dependence on the amount of TiO2.However,the inhomogeneity of the heat-affected zone near different base metals presented no significant effect on the mechanical properties of the welded joint.

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.