Effect of process parameters on the morphology of aluminum/copper alloy lap joints by red and blue hybrid laser welding

In order to overcome the problems of many pores,large deformation and unstable weld quality of traditional laser welded aluminumcopper alloy joints,a red-blue dual-beam laser source and a swinging laser were introduced for welding.T2 copper and 6063 aluminum thin plates were lap welded by coaxial dual-beam laser welding.The morphology of weld cross section was compared to explore the influence of process parameters on the formation of lap joints.The microstructure characteristics of the weld zone were observed and compared by optical microscope.The results show that the addition of laser beam swing can eliminate the internal pores of the weld.With the increase of the swing width,the weld depth decreases,and the weld width increases first and then decreases.The influence of welding speed on the weld cross section morphology is similar to that of swing width.With the increase of welding speed,the weld width increases first and then decreases,while the weld depth decreases all the time.This is because that the red laser is used as the main heat source to melt the base metals,with the increase of red laser power,the weld depth increases.As an auxiliary laser source,blue laser reduces the total energy consumption,consequently,the effective heat input increases and the spatter is restrained effectively.As a result,the increase of red laser power has an enhancement effect on the weld width and weld depth.When the swing width is 1.2 mm,the red laser power is 550 W,the blue laser power is 500 W,and the welding speed is 35 mm/s,the weld forming is the best.The lap joint of T2 copper and 6063 aluminum alloy thin plate can be connected stably with the hybrid of blue laser.The effect rules of laser beam swing on the weld formation were obtained,which improved the quality of the joints.

Microstructures and properties analysis of dissimilar metal joint in the friction stir welded copper to aluminum alloy

This paper mainly concentrated on the feasibility of friction stir welding of dissimilar metal of aluminum alloy to copper （I2） and a preliminary analysis of welding parameters influencing on the microstructures and properties of joint was carried out. The results indicated that the thickness of workpiece played an important role in the welding parameters which could succeed in the friction stir welding of dissimilar metal of copper to aluminum alloy, and the parameters were proved to be a narrow choice. The interfacial region between copper and aluminum in the dissimilar joint was not uniformly mixed, constituted with part of incomplete mixing zone, complete mixing zone, dispersion zone and the most region＇ s boundary was obvious. Meantime a kind banded structure with inhomogeneous width was formed. The intermetallic compounds generated during friction stir welding in the interfacial region were mainly CugAl4, Al2Cu etc, and their hardness was higher than oihers.

An investigation on the performance of stress corrosion cracking in aluminum-copper alloy welded joint

With the resistance to stress corrosion of the base metal as a reference, the contrast result of stress corrosion cracking （ SCC） susceptibility of aluminum-copper alloy 2219 and 2014 welded joints under different welding processes （ VP-TIG welding, HF-TIG hybrid welding, laser-TIG hybrid welding and laser HF-TIG hybrid welding） is obtained via the slow strain rate testing （ SSRT） , scanning electron microscope （ SEM） and microstructure observation auxiliary technologies. Test results show that the joints of aluminum alloy 2219, welded by hybrid welding processes, have superior resistance to stress corrosion compared to those welded by the VP-TIG welding process in varying degrees, especially, the joint welded by the laser HF-TIG hybrid welding process, where the resistance to stress corrosion is almost the same as that of the base material. However, the HF or laser hybrid welding effect is not significant under the same welding conditions for welded joints of aluminum alloy 2014.

Effects of electron beam welding parameters on the microstructure of titanium to aluminum alloy joints

Electron beam welding of titanium alloy to aluminum alloy was carried out by melting and melt-brazing to investigate the effects of welding parameters on microstructure of the joint. The results indicated that the joint of the specimen welded by melting was well-formed but contained a large amount of intermetallic compounds. These intermetallic compounds were mainly composed of brittle phases such as TiAl and TiAl3 that decreased the ductility of the joints and resulted in a tensile strength 50 % lower than that of the base metal. In the melt-brazing experiment, direct heat was applied to the aluminum alloy to melt the aluminum rather than the titanium alloy, creating a well-formed joint. The weld was mainly composed of Al element and only a 3 ~m thickness of intermetallic compounds formed near the fusion line at the Ti side. The ductility and the performauce of the joint were significantly improved compared with those of the melting-only joint. In addition, the tensile strength of the joint reached 80 % of that of the aluminum base metal.

Microstructure and mechanical properties of the welding joint filled with microalloying 5183 aluminum welding wires

In this study, 7A52 aluminum alloy sheets of 4 mm in thickness were welded by tungsten inert gas welding using microalloying welding wires containing traces of Zr and Er. The influence of rare earth elements Zr and Er on the microstructure and mechanical properties of the welded joints was analyzed by optical microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, hardness testing, and tensile mechanical properties testing. Systematic analyses indicate that the addition of trace amounts of Er and Zr leads to the formation of fine Al3Er, Al3Zr, and Al3（Zr,Er） phases that favor significant grain refinement in the weld zone. Besides, the tensile strength and hardness of the welded joints were obviously improved with the addition of Er and Zr, as evidenced by the increase in tensile strength and elongation by 40 MPa and 1.4%, respectively, and by the welding coefficient of 73%.

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.

Structure and mechanical properties of aluminum alloy/Ag interlayer/steel non-centered electron beam welded joints

Electron beam welding was carried out between aluminum alloy and steel with Ag interlayer. Seam morphology, structure and mechanical properties of the joints were investigated with different action positions of the electron beam spot. The results show that with the increment of the beam offset to the silver side from the interface between silver and steel, the seam morphology was improved, and the porosity in the Ag interlayer vanished. A transition layer mainly composed of Ag2Al and Al eutectic was formed at the interface between silver and aluminum, and became thin and spiccato as the beam offset increased. When the beam offset was too large, two IMC layers composed of FeAl and FeAl3 respectively were formed at the interface between steel and Ag interlayer. The optimal beam offset was 0.2 mm, and the maximum tensile strength of the joint was 193 MPa, 88.9% that of the aluminum alloy, and the fracture occurred at the interface between steel and Ag interlayer.

Fatigue Behavior of a Dissimilar Aluminum Alloy Welding Joint With and Without Natural Defect

In order to investigate the influence of natural defect on the fatigue behavior of 5A06/7A05 dissimilar aluminum alloys welding joint,fatigue tests of two types of specimens with and without defects were carried out systematically under stress amplitude control conditions (stress ratio R=0.1) at normal temperature in laboratory air condition.Furthermore,a new parameter,i e,fatigue defect effect factor (FDEF) was introduced to assess the effect of defect on fatigue strength.The fatigue failure analysis was conducted as well to compare the fatigue and fracture behavior of the two types of specimens.The results show that:(1) natural defects have a strong effect on the fatigue lives of welding joint,and the differences between the specimens with and without defects can reach 80 times under a same theoretical net sectional stress;(2) the FDEF parameter introduced is effective to deal with the defect effect,and the FDEF decreases along with the increase of fatigue life.The mean relative error between the experimental data and predicted fatigue strength based on the FDEF is 10.2%;(3) the macro fracture of both types of specimens have three typical zones,i e,fatigue source zone,crack propagation zone and final fracture zone,while there are more than one fatigue sources for specimens with natural defects.The overall pattern of crack propagation zone and fracture zone are quite similar,but the morphologies are different in details.

Numerical analysis of temperature profile and weld dimensions in laser ＋ GMAW hybrid welding of aluminum alloy T-joint

The temperature fields in the transient state and weld dimensions in laser ＋ gas metal arc welding （GMAW） hybrid welding of aluminum alloy T-joint for different welding conditions were calculated using the developed heat source model, and the effect of welding speed on them was analyzed. The results show that the temperature field for the first weld pass only shows the feature of GMAW and the one for the second weld pass has the characteristics of both laser welding and GMAW. Welding speed can affect greatly weld dimensions and temperature distribution. When welding speed reaches 3.5 m/min, the fusion zones of two weld passes are separated and the maximum peak temperature of thermal cycle on the workpiece surface decreases largely.

Prediction of vulnerable zones based on residual stress and microstructure in CMT welded aluminum alloy joint

Numerical simulation and experimental results were employed for the identification of the most vulnerable zones in three-pass cold-metal-transferring （CMT） welded joint. The residual stress distribution in the joint was predicted by finite element （FE） method, while the structural morphology of distinctive zones was obtained through metallographic experiments. The highest principal stress made the symmetric face of the joint most sensitive to tensile cracks under service conditions. Whereas, the boundaries between the weld seam and the base plates were sensitive to cracks because the equivalent von Mises stress was the highest when the first interpass cooling was finished. The third weld pass and the inter-pass remelted zones exhibited the modest mechanical performances as a result of the coarse grain and coarse grain boundary, respectively. The most vulnerable zones were regarded to be the crossed parts between the zones identified by numerical and experimental methods.

Effect of intermetallic compounds on the fracture behavior of dissimilar friction stir welding joints of Mg and Al alloys

Joining Mg to Al is challenging because of the deterioration of mechanical properties caused by the formation of intermetallic compounds(IMCs) at the Mg/Al interface. This study aims to improve the mechanical properties of welded samples by preventing the fracture location at the Mg/Al interface. Friction stir welding was performed to join Mg to Al at different rotational and travel speeds. The microstructure of the welded samples showed the IMCs layers containing Al12Mg17(γ) and Al3Mg2(β) at the welding zone with a thickness(< 3.5 μm). Mechanical properties were mainly affected by the thickness of the IMCs, which was governed by welding parameters. The highest tensile strength was obtained at 600 r/min and 40 mm/min with a welding efficiency of 80%. The specimens could fracture along the boundary at the thermo-mechanically affected zone in the Mg side of the welded joint.

Corrosion behavior of the friction-stir-welded joints of 2A14-T6 aluminum alloy

The corrosion behavior of friction-stir-welded 2A14-T6 aluminum alloy was investigated by immersion testing in immersion exfoliation corrosion（EXCO） solution. Electrochemical measurements（open circuit potential, potentiodynamic polarization curves, and electrochemical impedance spectroscopy）, scanning electron microscopy, and energy dispersive spectroscopy were employed for analyzing the corrosion mechanism. The results show that, compared to the base material, the corrosion resistance of the friction-stir welds is greatly improved, and the weld nugget has the highest corrosion resistance. The pitting susceptibility originates from the edge of Al-Cu-Fe-Mn-Si phase particles as the cathode compared to the matrix due to their high self-corrosion potential. No corrosion activity is observed around the θ phase（Al2Cu） after 2 h of immersion in EXCO solution.

Interfacial characterization of resistance spot welded joint of steel and aluminum alloy

The dissimilar material resistance spot welding of galvanized high strength steel and aluminum alloy had been conducted. The welded joint exhibited a thin reaction layer composed of Fe2Al5 and Fe4Al13 phases at steel/aluminum interface. The welded joint presented a tensile shear load of 3.3 kN with an aluminum alloy nugget diameter of 5.7 mm. The interfacial failure mode was observed for the tensile shear specimen and fracture occurred at reaction layer and aluminum alloy fusion zone beside the interface. The reaction layer with compounds was the main reason for reduction of the welded joint mechanical property.

Void damage evolution of LF6 aluminum alloy welded joints under external load and thermal cycling conditions

Based on the simulated aerospace thermal cycling tests,the effect of thermal cycle on the void damage evolution mechanism of LF6 aluminum alloy welded joint was investigated.The results show that micro-voids form around the second phase particles under the thermal cycling tests.The thermal stress coupled with external stress leads to dislocations pile-up around the particles,and when the dislocation density reaches a certain degree,the stress concentration will exceed the bonding strength at the interface between particles and matrix,resulting in the formation of micro-cracks.The numerical simulation is successfully implemented with the finite element to describe the void damage evolution of the welded joint under thermal cycling conditions.

Microstructure and mechanical property of resistance spot welded joint of aluminum alloy to high strength steel with especial electrodes

Dissimilar material joining of 6008 aluminum alloy to H220 YD galvanized high strength steel was performed by resistance spot welding with especial electrodes that were a flat tip electrode against the steel surface and a domed tip electrode upon the aluminum alloy surface. An intermetallic compound layer composed of Fe2Al5 and FeAl3 was formed at the steel/ aluminum interface in the welded joint. The thickness of the intermetallic compound layer increased with increasing welding current and welding time, and the maximum thickness being 7. 0 μm was obtained at 25 kA and 300 ms. The weld nugget diameter and tensile shear load of the welded joint had increased tendencies first with increasing welding current （ 18 -22 kA） and welding time （ 50 - 300 ms）, then changed little with further increasing welding current （ 22 - 25 kA） and welding time （300 -400 ms）. The maximum tensile shear load reached 5.4 kN at 22 kA and 300 ms. The welded joint fractured through brittle intermetallic compound layer and aluminum alloy nugget.

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.

Fatigue property comparison of TIG welded joints of magnesium alloy and aluminum alloy

The fatigue properties of the TIG welded joints of both AZ31B magnesium alloy and 5A06 aluminum alloy were investigated. The four types of welded joints were used in fatigue tests, such us butt joints, transverse cross joints, fillet joints and lateral connecting joints. The fatigue strengths at 2 × 10^6 cycles of the four welded joints of AZ31B magnesium alloy are 39. 0 MPa, 24. 4 MPa, 32. 1 MPa and 24. 2 MPa, which are 55. 0% , 42. 2%, 78. 0% and 50. 2% of that of 5A06 aluminum alloy, respectively. The fatigue strength levels at slope m = 3 of the aluminum alloy＇ s welded joints are mostly higher than the FAT recommended by the International Institute of Welding （ HW） , while those of the magnesium alloy＇ s welded joints are all lower than the FAT. It is indicated that the FAT of magnesium alloy＇ s welded joints should be established as early as possible in order to be applied in the design of magnesium alloy＇ s welded structures.

Joint performance of CO2 laser-MIG hybrid welding 5083-H116 alloy

Laser-MIG hybrid welding process was dealt with 6 mm thick 5083Hl16 Al-Mg alloy plate in butt-joint configuration. Weld formation principle during hybrid welding was explained. The joint properties and microstructure characteristics of welded joints were analyzed by tensile tests, fractographs observed by optical microscopy and scanning electron microscopy （SEM）. Higher heat input could obtain better mechanical properties, and tensile strength and elongation reached 97.2%, 81% of the base metal, respectively. Fracture position traasited from fusion line to weld center in the higher heat input, and fracture location were only in the center of welded joints for the heat input relatively small.

Defects of friction stir welded 1060 aluminum alloy and their effects on joint tensile property

9. 6 mm thick 1060-H24 aluminum alloy plates were friction stir welded and the influencing factors on groove and tunnel defects were examined. Results show that the welding speed range for achieving a groove-free joint is enlarged with increasing the rotating speed. The tunnel size decreases with decreasing the welding speed under the same rotating speed. Excessive or insufficient shoulder plunge depth will cause defective joints. At a relatively low rotating speed and high welding speed, the tool having a larger shoulder diameter has a larger range of processing parameters to obtain a groove-free joint. Moreover, the tensile fracture behaviors of the defective and defect-free samples are different.

Determination of local constitutive behavior and simulation on tensile test of 2219-T87 aluminum alloy GTAW joints

The local and global mechanical responses of gas tungsten arc welds（GTAW） of a 2219-T87 aluminum alloy were investigated with experiment and numerical simulation.Digital image correlation（DIC） was used to access the local strain fields in transversely loaded welds and to determine the local stress-strain curves of various regions in the joint.The results show that the DIC method is efficient to acquire the local stress-strain curves but the curves of harder regions are incomplete because the stress and strain ranges are limited by the weakest region.With appropriate extrapolation,the complete local stress-strain curves were acquired and proved to be effective to predict the tensile behavior of the welded joint.During the tensile process,the fracture initiates from the weld toes owing to their plastic strain concentrations and then propagates along the fusion line,finally propagates into the partially melted zone（PMZ）.