Microstructure characteristics and corrosion behavior of metal inert gas welded dissimilar joints of 6005A modified by Sc and 5083 alloys

The corrosion behavior and microstructure characteristics of metal inert gas(MIG)welded dissimilar joints of the 6005A alloy modified with Sc(designated as 6005A+Sc)and the 5083 alloy were investigated using corrosion tests and microscopy techniques.Results show that the dissimilar joints exhibit strong stress corrosion cracking(SCC)resistance,maintaining substantial strength during slow strain rate tensile tests.Notably,the heat-affected zone(HAZ)and base metal(BM)on the 6005A+Sc side show superior performance in terms of inter-granular corrosion(IGC)and exfoliation corrosion(EXCO)compared to the corresponding zones on the 5083 side.The lower corrosion resistance of the 5083-BM and the 5083-HAZ can be attributed to the presence of numerous Al_(2)Mg_(3)phases and micro-scaled Al_(6)(Mn,Fe)intermetallics,mainly distributed along the rolling direction.Conversely,the enhanced corrosion resistance of the 6005A+Sc-BM and the 6005A+Sc-HAZ can be attributed to the discontinuously distributed grain boundary precipitates(β-Mg_(2)Si),the smaller grain size,and the reduced corrosive current density.

Effect of Interface Form on Creep Failure and Life of Dissimilar Metal Welds Involving Nickel-Based Weld Metal and Ferritic Base Metal

For dissimilar metal welds(DMWs)involving nickel-based weld metal(WM)and ferritic heat resistant steel base metal(BM)in power plants,there must be an interface between WM and BM,and this interface suffers mechanical and microstructure mismatches and is often the rupture location of premature failure.In this study,a new form of WM/BM interface form,namely double Y-type interface was designed for the DMWs.Creep behaviors and life of DMWs containing double Y-type interface and conventional I-type interface were compared by finite element analysis and creep tests,and creep failure mechanisms were investigated by stress-strain analysis and microstructure characterization.By applying double Y-type interface instead of conventional I-type interface,failure location of DMW could be shifted from the WM/ferritic heat-affected zone(HAZ)interface into the ferritic HAZ or even the ferritic BM,and the failure mode change improved the creep life of DMW.The interface premature failure of I-type interface DMW was related to the coupling effect of microstructure degradation,stress and strain concentrations,and oxide notch on the WM/HAZ interface.The creep failure of double Y-type interface DMW was the result of Type IV fracture due to the creep voids and micro-cracks on fine-grain boundaries in HAZ,which was a result of the matrix softening of HAZ and lack of precipitate pinning at fine-grain boundaries.The double Y-type interface form separated the stress and strain concentrations in DMW from the WM/HAZ interface,preventing the trigger effect of oxide notch on interface failure and inhibiting the interfacial microstructure cracking.It is a novel scheme to prolong creep life and enhance reliability of DMW,by means of optimizing the interface form,decoupling the damage factors from WM/HAZ interface,and then changing the failure mechanism and shifting the failure location.

Microstructure and thermal properties of dissimilar M300–CuCr1Zr alloys by multi-material laser-based powder bed fusion

Multi-material laser-based powder bed fusion (PBF-LB) allows manufacturing of parts with 3-dimensional gradient and additional functionality in a single step. This research focuses on the combination of thermally-conductive CuCr1Zr with hard M300 tool steel.Two interface configurations of M300 on CuCr1Zr and CuCr1Zr on M300 were investigated. Ultra-fine grains form at the interface due to the low mutual solubility of Cu and steel. The material mixing zone size is dependent on the configurations and tunable in the range of0.1–0.3 mm by introducing a separate set of parameters for the interface layers. Microcracks and pores mainly occur in the transition zone.Regardless of these defects, the thermal diffusivity of bimetallic parts with 50vol% of CuCr1Zr significantly increases by 70%–150%compared to pure M300. The thermal diffusivity of CuCr1Zr and the hardness of M300 steel can be enhanced simultaneously by applying the aging heat treatment.

Failure Analysis of Dissimilar Metal Welds between Ferritic Heat Resistant Steels and Austenitic Stainless Steels in Power Plant

This study analysed the failure of dissimilar metal welds(DMWs)between ferritic heat resistant steels and austenitic stainless steels and investigated its influencing factors by means of numerical simulation,microstructure characterization and mechanical property test.Under the long-term high-temperature service condition in practical power plant,the DMW failure mode was along the interface between nickel-based weld metal(WM)and ferritic heat resistant steel,and the failure mechanism was stress/strain concentration,microstructure degradation and oxidation coupling acting on the interface.The numerical simulation results show that interface stress/strain concentration was due to the differences in coefficient of thermal expansion and creep strength,and the degree of stress/strain concentration was related to service time.The ferrite band formed at the WM/ferritic steel interface was prone to cracking,attracting the fracture along the interface.The interface crack allowed oxidation to develop along the WM/ferritic steel interface.During long-term service,the interface stress/strain concentration,microstructure and oxidation all evolved,which synergistically promoted interface failure of DMW.However,only under the long-term service of low stress conditions could trigger the interface failure of DMW.Meanwhile,long-term service would reduce the mechanical strength and plasticity of DMW.

Microstructure,Corrosion and Mechanical Properties of Medium-Thick 6061-T6 Alloy/T2 Pure Cu Dissimilar Joints Produced by Double Side Friction Stir Z Shape Lap-Butt Welding

A novel double side friction stir Z shape lap-butt welding(DS-FSZW)process was proposed to achieve excellent mechanical properties of Al/Cu medium-thick dissimilar joints.The influence of welding parameters on weld microstructure and properties of DS-FSZW joint were systematically investigated.It indicated that defect-free medium-thick Al/Cu DS-FSZW joint could be achieved under an optimal welding parameter.DS-FSZW joint was prone to form void defects in the bottom of the second-pass weld.The recrystallization mechanisms at the top and middle of the weld nugget zone(WNZ)were continuous dynamic recrystallization(CDRX)and geometric dynamic recrystallization(GDRX).While the major recrystallization mechanism at the bottom of the WNZ was GDRX.DS-FSZW joint of the optimal welding condition with 850 r/min-400 mm/min was produced with a continuous thin and crack-free IMCs layer at the Al/Cu interface,and the maximum tensile strength of this joint is 160.57 MPa,which is equivalent to 65.54%of pure Cu base material.Moreover,the corrosion resistance of Al/Cu DS-FSZW joints also achieved its maximum value at the optimal welding parameter of 850 r/min-400 mm/min.It demonstrates that the DS-FSZW process can simultaneously produce medium-thick Al/Cu joints with excellent mechanical performance and corrosion resistance.

Synthesis of organic-inorganic 3D-nanocontainers for smart corrosion protection of friction stir welded AZ31B magnesium alloy-titanium dissimilar joints

The joining of different light metals through friction stir welding(FSW)is gaining interest as a method to decrease weight and improve fuel efficiency.However,to ensure durability,these welded metals may require surface treatments to protect against corrosion or wear.This study presents a novel approach for the simultaneous delivery of two distinct corrosion inhibitors to Ti-Mg dissimilar PEO treated joints on demand.The research focuses on the synthesis,characterization,and application of cerium@polystyrene(Ce@PS)nanocontainers,which are loaded with 8-hydroxyquinoline(8-HQ)to enhance corrosion protection.The synthesis involves several key steps,including the formation of a cerium-based outer layer around polystyrene nanospheres,the selective removal of the polystyrene core to create a porous structure,and the subsequent loading of the 8-HQ inhibitor.Structural and compositional analyses,conducted using scanning transmission electron microscopy(STEM)and energy-dispersive X-ray spectroscopy(EDS),confirmed the successful incorporation of 8-HQ within the nanocontainers.Additionally,Fourier-transform infrared spectroscopy(FTIR)provided detailed information about the chemical composition of the organic materials throughout the synthesis process.Thermal decomposition analysis verified the successful fabrication and stability of the dual-shell nanocontainers.Corrosion tests on Ti-Mg joints treated with plasma electrolytic oxidation(PEO)coatings and loaded nanocontainers demonstrated sig-nificantly improved corrosion resistance compared to untreated joints.This research highlights the potential of dual-shell nanocontainers,containing both organic and inorganic inhibitors,to offer prolonged corrosion protection,particularly against galvanic corrosion in dissimilar joints.The findings suggest that these synthesized nanocontainers hold promise for various industrial applications,particularly in the context of friction stir welded(FSW)Ti-Mg dissimilar joints,providing valuable insights for the development of advanced materials designed to mitigate corrosion.

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.

Microstructure and mechanical properties of dissimilar Al-Cu joints by friction stir welding

Dissimilar friction stir welding between 1060 aluminum alloy and annealed pure copper sheet with a thickness of 3 mm was investigated. Sound weld was obtained at a rotational speed of 1050 r/min and a welding speed of 30 mm/min. Intercalation structure formed at the crown and Cu/weld nugget （WN） area promotes interracial diffusion and metallurgical bonding of aluminum and copper. However, corrosion morphology reveals the weak bonding mechanism of internal interface, which causes the joint failing across the interface with a brittle-ductile mixed fracture mode. The tensile strength of the joint is 148 MPa, which is higher than that of the aluminum matrix. Crystal defects and grain refinement by severely plastic deformation during friction stir welding facilitate short circuit diffusion and thus accelerate the formation of A14Cu9 and A12Cu intermetallic compounds （IMCs）. XRD results show that A14Cu9 is mainly in Cu/WN transition zone. The high dislocation density and formation of dislocation loops are the major reasons of hardness increase in the WN.

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.

Microstructures and mechanical properties of metal inert-gas arc welded Mg-steel dissimilar joints

The joining of Mg alloy to steel was realized by metal inert-gas arc welding, and the weld thermal cycle characteristics and Mg-steel joints were investigated. The results show that the temperature distribution in the joints is uneven. Mg alloy welds present a fine equiaxed grain structure. There exists a transition layer consisting mainly of AlFe, AlFe3 and Mg（Fe, Al）2O4 phases at Mg/steel interface, and it is the weakest link in Mg？steel joints. The welding heat input and weld Al content have the significant effect on the joint strength. The joint strength increases with increasing the heat input from 1680 J/cm to 2093 J/cm, due to promoting Mg/steel interface reaction. When weld Al content is increased to 6.20%, the joint strength reaches 192 MPa, 80% of Mg alloy base metal strength. It is favorable to select the suitable welding heat input and weld Al content for improving joint strength.

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.

Effect of welding process on the microstructure and properties of dissimilar weld joints between low alloy steel and duplex stainless steel

To obtain high-quality dissimilar weld joints, the processes of metal inert gas （MIG） welding and tungsten inert gas （TIG） welding for duplex stainless steel （DSS） and low alloy steel were compared in this paper. The microstructure and corrosion morphology of dissimilar weld joints were observed by scanning electron microscopy （SEM）; the chemical compositions in different zones were detected by en- ergy-dispersive spectroscopy （EDS）; the mechanical properties were measured by microhardness test, tensile test, and impact test; the corro- sion behavior was evaluated by polarization curves. Obvious concentration gradients of Ni and Cr exist between the fusion boundary and the type II boundary, where the hardness is much higher. The impact toughness of weld metal by MIG welding is higher than that by TIG weld- ing. The corrosion current density of TIG weld metal is higher than that of MIG weld metal in a 3.5wt% NaC1 solution. Galvanic corrosion happens between low alloy steel and weld metal, revealing the weakness of low alloy steel in industrial service. The quality of joints pro- duced by MIG welding is better than that by TIG welding in mechanical performance and corrosion resistance. MIG welding with the filler metal ER2009 is the suitable welding process for dissimilar metals jointing between UNS $31803 duplex stainless steel and low alloy steel in practical application.

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.

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.

Optimization of gas tungsten arc welding parameters for the dissimilar welding between AISI 304 and AISI 201 stainless steels

This present study applied gas tungsten arc welding in order to join AISI 304 and AISI 201 stainless steels.The objective was to find the optimum welding condition that gave a weld bead in accordance with DIN EN ISO 25817 quality level B, pitting corrosion potential of the weld metal of not less than that of the AISI304 base metal and a ratio of delta-ferrite in austenite matrix of the weld metal of not lower than 3%.Such a ratio is a criterion widely accepted to protect the weld metal from solidification cracking. At the welding current of 75 A and by using pure argon as a shielding gas 0 to 8 vol.% and applying a welding speed in the range of 2-3.5 mm·s^(-1) was found to give a complete weld bead with an increased depthper-width ratio(promote weldability). For welding speed in the range of 3 and 3.5 mm·s^(-1)(promote corrosion resistance). Increasing the welding speed in such a range decreased the amount of delta-ferrite in the austenite matrix, and increased the pitting corrosion potential of the weld metal to be 302 mV_(SCE).This value was still lower than the pitting corrosion potential of the AISI 304 base metal. Mixing nitrogen in argon shielding gas increased the nitrogen content in the weld. The optimum condition was found when using a welding speed of 3 mm· s^(-1) and mixing 1 vol.% of nitrogen in the argon shielding gas(promote weldability and corrosion resistance). Pitted areas after potentiodynamic test were observed in the austenite in which its Cr content was relatively low.

Microstructure and mechanical properties of laser beam welded TC4/TA15 dissimilar joints

The microstructure and mechanical properties of laser beam welded dissimilar joints in TC4 and TA15 titanium alloyswere investigated. The results showed that the coarse columnar grains containing a large amount of acicular α and martensite α′ werepresent in the fusion zone (FZ), some residual α phases and martensite structure were formed in the heat-affected zone (HAZ) onTC4 side, and bulk equiaxed α phase of the HAZ was on TA15 side. An asymmetrical microhardness profile across the dissimilarjoint was observed with the highest microhardness in the FZ and the lowest microhardness in TA15 BM. The orders of yield strengthand ultimate tensile strength were as follows: TC4 BM > TC4/TC4 similar joint > TA15 BM > TA15/TA15 similar joint > TC4/TA15dissimilar joint, and increased while hardening capacity and strain hardening exponent decreased with increasing strain rate from1×10?4 s?1 to 1×10?2 s?1. The TC4/TA15 dissimilar joints failed in the TA15 BM, and had characteristics of ductile fracture atdifferent strain rates.

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 mechanical properties of dissimilar pinless friction stir spot welded 2A12 aluminum alloy and TC4 titanium alloy joints

The microstructure and mechanical properties of dissimilar pinless friction stir spot welded joint of2A12aluminum alloy and TC4titanium alloy were evaluated.The results show that the joint of Al/Ti dissimilar alloys can be successfully attained through pinless friction stir spot welding(FSSW).The joint can be divided into three zones(SZ,TMAZ and HAZ).The microstructure of joint in Al alloy side changes significantly but it basically has no change in Ti alloy side.At the same rotation speed,the maximum load of welded joints gradually rises with the increase in dwell time.At the same dwell time,the maximum load of the welded joint increases with the increase of the rotational speed.In addition,optimal parameters were obtained in this work,and they are rotation speed of1500r/min,plunge speed of30mm/min,plunge depth of0.3mm and dwell time of15s.The fracture mode of welded joints is interfacial shear fracture.The microhardness of the joint on the Al side distributes in a typical“W”type and is symmetry along the weld center,but the distribution of the microhardness on the Ti side has no obvious change.

Electrochemical corrosion behaviour of stir zone of friction stir welded dissimilar joints of AA6061 aluminium-AZ31B magnesium alloys

Joining of dissimilar metals will offer many advantages in transportation sectors such as fuel consumption,weightreduction and emission reduction.However,joining of aluminium(Al)alloys with magnesium(Mg)alloys by fusion welding processis very complicated.Friction stir welding(FSW)is a feasible method to join these two dissimilar alloys.Mixing these two metalstogether in stir zone(SZ)leads to poor corrosion resistance.In this investigation,an attempt has been made to understand thecorrosion resistance of SZ of FSWed dissimilar joints of AA6061Al alloy and AZ31B Mg alloy.Potentiodynamic polarization testwas conducted by varying chloride ion concentration,pH value of the NaCl solution and exposure time.The corroded surfaces wereanalyzed using optical microscopy,scanning electron microscopy and XRD techniques.Of these three factors investigated,exposuretime is found to be the most significant factor to influence the corrosion behaviour of SZ of friction stir welded dissimilar joints ofAl/Mg alloys.

Microstructure and mechanical properties of dissimilar steel plate resistance plug welding joints

A new type of hybrid welding method called resistance plug welding （RPW） was firstly adopted to achieve the connecting of dissimilar steel, mainly as for the poor welding characteristics of high strength steel produced by increasing carbon, manganese, silicon, etc. Microstructures and mechanical properties of RPW joint were analyzed by optical microscope,micro-hardness test and shear tensile measurement. Experimental results indicate that the RPW joint has a rounded rectangle nugget ^ and the size is larger than elliptical nugget of resistance spot welding （RSW） jo in t; the hardness value of RPW joint is evenly distributed, accordingly there is no hard brittle phases ; the shear tensile strength o f RPW joint increases by 20% in comparison with RSW joint under the same welding conditions.