Effects of electromagnetic stirring on microstructure and mechanical properties of super light Mg-Li-Al-Zn alloy

Effects of electromagnetic stirring on the microstructure and mechanical properties of the magnesium-lithium-aluminum alloy were studied.The results reveal that,the morphology of theαphase changes from the long block to globular structure andβ phase distributes more widely in the periphery ofαphase when the electromagnetic stirring voltage is higher than 110 V.The mechanical properties are increased significantly with the increasing electromagnetic stirring.The tensile strength is improved from 172 to 195 MPa,and the elongation is increased from 10.65%to 25.75%.

Microstructure and mechanical properties of stationary shoulder friction stir welding joint of 2A14-T62 aluminum alloy

2A14-T62 butt joint was successfully welded by stationary shoulder friction stir welding(SSFSW)method.The results showed that using a pin with small shoulder could broaden the process window,and under a rotation speed of 2000 r/min and welding speed of 30 mm/min,joint with smooth surface,small reduction in thickness and little inner defects was obtained.The weld nugget zone was approx-imately circular,which was a unique morphology for SSFSW.The heat-affected zone(HAZ)and thermo-mechanically affected zone(TMAZ)were both quite narrow due to the lower heat input and slight mechanical action of the stationary shoulder.The fraction of high angle grain boundaries(HAGBs)exhibited a“W”shape along horizontal direction(from advancing side to retreating side),and the minim-um value located at HAZ.The average ultimate tensile strength and elongation of the joint were 325 MPa and 4.5%,respectively,with the joint efficiency of 68.3%.The joint was ductile fractured and the fracture surface contained two types of dimples morphology in different re-gions of the joint.Microhardness distribution in the joint exhibited a“W”shape,and the difference along the thickness direction was negli-gible.The joint had strong stress corrosion cracking susceptibility,and the slow stain rate tensile strength was 139 MPa.Microcrack and Al2O3 particulates were observed at the fracture surface.

Improvement of Microstructure and Mechanical Properties of Rapid Cooling Friction Stir-welded A1050 Pure Aluminum

Two-mm thick A1050 pure aluminum plates were successfully joined by conventional and rapid cooling friction stir welding(FSW), respectively. The microstructure and mechanical properties of the welded joints were investigated by electron backscatter diffraction characterization, Vickers hardness measurements, and tensile testing. The results showed that liquid CO_(2) coolant significantly reduced the peak temperature and increased the cooling rate, so the rapidly cooled FSW joint exhibited fine grains with a large number of dislocations. The grain refinement mechanism of the FSW A1050 pure aluminum joint was primarily attributed to the combined effects of continuous dynamic recrystallization, grain subdivision, and geometric dynamic recrystallization. Compared with conventional FSW, the yield strength, ultimate tensile strength, and fracture elongation of rapidly cooled FSW joint were significantly enhanced, and the welding efficiency was increased from 80% to 93%. The enhanced mechanical properties and improved synergy of strength and ductility were obtained due to the increased dislocation density and remarkable grain refinement. The wear of the tool can produce several WC particles retained in the joint, and the contribution of second phase strengthening to the enhanced strength should not be ignored.

Mechanical properties and microstructural evolution of rheocast A356 semi-solid slurry prepared by annular electromagnetic stirring

Nowadays,having an effective technique in preparing semi-solid slurries for rheocasting process seems to be an essential requirement.In this study,semi-solid slurry of A356 aluminum alloy was prepared by three-phase annular electromagnetic stirring(A-EMS)technique under different conditions.The effects of stirring current,pouring temperature and stirring time on microstructural evolution,mean particle size,shape factor and solid fraction were investigated.The rheocasting process was carried out by using a drop weight setup and to inject the prepared semi-solid slurry in optimal conditions into the step-die cavity.The filling behavior and mechanical properties of parts were studied.Microstructural evolution showed that the best semi-solid slurry which had fine spherical particles with the average size of~27μm and a shape factor of~0.8 was achieved at the stirring current of 70 A,melt pouring temperature of 670℃,and stirring time of 30 s.Under these conditions,the step-die cavity was completely filled at die preheating temperature of 470℃.The hardness increases by decreasing step thickness as well as die preheating temperature.Moreover,the tensile properties are improved at lower die preheating temperatures.The fracture surface,which consists of a complex topography,indicates a typical ductile fracture.

A high-Nb TiAl alloy with highly refined microstructure and excellent mechanical properties fabricated by electromagnetic continuous casting

In the present research, microstructure refinement of a high-Nb TiAl alloy （Ti-48Al-8Nb-0.15B） was realized by means of the electromagnetic continuous casting （EMCC） technique. The microstructure of an ingot obtained by EMCC was analyzed using scanning electron microscopy （SEM）. As compared with the raw as-cast alloy, the obtained EMCC alloy presented a much finer microstructure with lamellar colonies with a mean size of about 50-70 μm because the electromagnetic stirring broke initial dendrites and enhanced the heterogeneous nucleation. As the grains were refined, the properties of the TiAl alloy were improved significantly. This implies that the EMCC technique could offer the possibility of application for high-Nb TiAl alloys with a refined microstructure and excellent properties to be used as a structural material.

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.

Effect of ultrasonic assisted friction stir welding on microstructure and mechanical properties of AZ91-C magnesium alloy

The influence of ultrasonic vibrations on microstructure and mechanical properties of the AZ91-C magnesium alloy after ultrasonic assisted friction stir welding(UaFSW)in comparison with conventional friction stir welding(FSW)was investigated.The FSW was applied at the rotational speed of 1400 r/min and welding speed of 40 mm/min and no defects were observed.Using the same welding parameters,the process was carried out with inducing ultrasonic vibrations to the weld line at the amplitude of 15μm.The microstructure of the specimens was observed with optical and scanning electron microscopy.The results indicate that a very fine microstructure is obtained in UaFSW with respect to that of conventional FSW.Moreover,β-Mg17Al12 coarse dendrites are segregated to very fine and partly spherical particles that homogeneously distribute inα-Mg matrix.This remarkably-modified morphology of microstructure attributed to severe plastic deformation comes from ultrasonic vibration and friction stirring effect.Tensile and hardness tests were performed to evaluate the mechanical properties of the welds.According to the results,the vibration greatly improves the mechanical properties of the conventional FSW joint.The tensile strength and hardness are increased from 195 MPa and HV 79 in conventional FSW to 225 MPa and HV 87 in UaFSW,respectively.

Effect of Ca addition on the microstructure and the mechanical properties of asymmetric double-sided friction stir welded AZ61 magnesium alloy

The effects of 2%Ca addition on the microstructure and the mechanical properties of the asymmetric double-sided friction stir welded magnesium alloy AZ61 were investigated.Compared to the Ca-free AZ61magnesium alloy,the addition of 2%Ca significantly refines the grains in the stir zone after welding.Due to the existence of thermally stable Al2Ca particles,there is no noticeable change in the grain size in the stir zone regardless of the welding heat input.The electron backscattered diffraction analysis at the center of the stir zone confirmed the significant deterioration of the(0001)texture strength from the addition of 2%Ca.The tensile test of the joint suggested that the addition of 2%Ca provides stable tensile properties to the joint regardless of the welding parameters.The critical(0001)texture strength that determines the ultimate tensile strength decreased from 20 to 15 by the Ca addition.The addition of Ca enhanced the deterioration of the plastic elongation when the(0001)texture strength increased.

Microstructure and mechanical properties of friction stir welded AA7075-T651 aluminum alloy thick plates

Friction stir butt welding of AA7075-T651 plates with thicknesses of 10 and 16 mm was investigated. Defect-free, full- penetration welds were obtained after careful process parameter selection. While the nuggets in both welds exhibited very fine reerystallized grains, and finer grains were observed in welds made on 10 mm thick plates. Microhardness surveys revealed that significant loss in hardness occurs in the heat-affected zone. The reduction in hardness due to the welding process is higher in the case of welds made on 16 mm thick plates. Welds made on 10 mm thick plates exhibited superior tensile properties compared with those made on 16 mm thick plates. Fracture during tensile test occurred in the heat-affected zone in both cases. TEM images of specimens revealed that the heat-affected zone consisted of widened precipitate-free zones along grain boundaries and partial dissolution of precipitates in the grain interiors. It is concluded that defect-free single pass welds can be made on AA7075-T651 thick plates using friction stir welding and the welds made on 10 mm thick plates exhibit high joint efficiency.

Influence of multipass high rotating speed friction stir processing on microstructure evolution,corrosion behavior and mechanical properties of stirred zone on AZ31 alloy

The influence of multipass high rotating speed friction stir processing(FSP)on the microstructure evolution,corrosion behavior,and tensile properties of the stirred zone(SZ)was investigated by EBSD,TEM,SEM,electrochemical workstation and electronic universal testing machine.The mean grain size of the SZ is significantly refined,and it increases with the increase of the processing pass.In addition to an obvious increase in the number,the distribution ofβ-Al12Mg17 precipitates also becomes more uniform and dispersed with increasing the processing pass.Compared with the as-received AZ31 alloy,the tensile properties of the SZ are hardly improved,but the corrosion resistances are significantly enhanced.The corrosion potential of the SZ prepared by 4-pass FSP is increased from−1.56 V for the unprocessed AZ31 alloy to−1.19 V,while the corrosion current is decreased from 1.55×10^−4 to 5.47×10^−5 A.

Microstructure and Mechanical Properties of Friction Stir Welded 7050-T7451 Aluminum Alloy Plates

7050-T7451 aluminum alloy plates was friction stir welded at different welding parameters.Mechanical properties of the joints were estimated according to tensile test and hardness test.The microstructure evolution during friction stir welding(FSW) was examined using optical microscope(OM) and transmission electron microscope(TEM).The nugget zone(NZ) has a recrystallized,fine equiaxed grain structure with high dislocation density.Strengthening precipitates appear to have gone to solution.Heat mechanical affected zone(TMAZ) was characterized by a highly bend deformed grain structure with partly dynamic recovery and dynamic recrystallization.The grain structure in heat affected zone(HAZ)is similar to that of the base metal with little growth in size and contained a relatively low dislocation density.Strengthening precipitates coarsen severely and the precipitated-free zone(PFZ) along the grain boundaries increase in width.The mechanical properties of the joints were affected by welding parameters with different microstructure and welding defects.The joint with largest tensile strength was welded at the parameters with tool traverse speed of 200 mm/min and rotation rate of 800 r/min,up to 88% of that of base metal.

Microstructure, mechanical properties and formability of friction stir welded dissimilar materials of IF-steel and 6061 Al alloy

AA 6061 alloy and interstitial-free(IF)steel plates were joined by the friction stir welding(FSW)method,and the microstructure,mechanical properties,and biaxial stretch formability of the friction stir welded(FSWed)parts were investigated.The results indicate that the FSWed parts showed optimum tensile strength during FSW with the 0.4-mm offset position of the tool.The Fe4Al13 intermetallic compound formed in the defect-free intersection of AA 6061 and IF-steel plates during FSW.The hardness of the IF-steel part of the FSWed region increased almost 90%relative to its initial hardness of HV0.2 105.The tensile and yield strengths of FSWed regions were approximately 170 MPa and 145 MPa,respectively.According to the formability tests,the Erichsen Index(EI)of the IF-steel,AA 6061,and the FSWed samples were determined to be 2.9 mm,1.9 mm,and 2.1 mm,respectively.The EI of the FSWed sample was almost the same as that of the AA 6061 alloy.However,it decreased compared with that of the IF-steel.The force at EI(FEI)was approximately 1180 N for the FSWed condition.This value is approximately 70%higher than that of AA 6061 alloy.

Effects of Trace Amount Modified SiC Nanoparticles and Electromagnetic Stirring (EMS) on Microstructure and Mechanical Properties of 7055 Aluminum Alloy

The effects of trace amount modified SiC nanoparticles and electromagnetic stirring(EMS)on mierostructures and mechanical properties of 7055 aluminum alloy are investigated experimentally.The result shows that the original developed coarse dendrite and columnar with obvious orientation microstructure turns into homogeneous equiaxed microstructure with the application of trace amount modified SiC nanoparticles and EMS.A minimum grain size is 96 μm and has been observed when the addition of modified SiC nanoparticles is 0.05%and the current of EMS is 100A.The ultimate tensile strength is increased by 15.8%and the elongation is improved by 50%compared to those without modified SiC nanoparticles and EMS.Moreover,the compound effects of trace amount modified SiC nanoparticles and EMS is discussed to explain the mechanisms of grain refinement and mechanical properties on 7055 aluminum alloy.

Effects of heat input in friction stir welding on microstructure and mechanical properties of AA3003-H18 plates

The non-heat-treatable AA3003-H18 plates were joined by friction stir welding（FSW） to achieve a proper joint by optimizing the welding parameters.For this purpose,the effects of heat input on microstructure and mechanical properties of the welded samples were investigated by changing the ratios of rotational speed（800-1200 r/min） to travel speed（40-100 mm/min）（w/v）.It was revealed that the grain growth rate was strongly increased with the increase of the heat input by rotational speed at constant travel speed,while the grain growth rate was slightly increased with the increase of the heat input by travel speed at constant rotational speed.Subsequently,hardness reduction was observed in the stir zone at higher rotational speed compared with that at lower one.An interesting observation was that various welding parameters do not have noticeable effect on the tensile strength of the FSW joints.Also,it has been observed that the fracture location of tensile test specimens was placed in the heat-affected zone（HAZ）on the advancing side at lower travel speed,while at higher travel speed,it was placed at the HAZ/thermomechanical affected zone（TMAZ） interface on the retreating side.

Impact of travel speed on the microstructure and mechanical properties of adjustable-gap bobbin-tool friction stir welded Al–Mg joints

The butt welds of 4-mm thick 5A06 aluminum alloy plates were produced by adjustable-gap bobbin-tool friction stir travel with travel speeds of 200, 300, and 400 mm/min in this study.The microstructure was studied using optical microscopy and electron backscatter diffraction(EBSD).Tensile tests and microhardness measurements were performed to identify the effect of the travel speed on the joint mechanical properties.Sound joints were obtained at 200 mm/min while voids were present at different positions of the joints as the travel speed increased.The EBSD results show that the grain size, high angle grain boundaries, and density of geometrically necessary dislocations in different regions of the joint vary depending on the recovery and recrystallization behavior.Specific attention was given to the relationship between the local microstructure and mechanical properties.Microhardness measurements show that the average hardness of the stir zone(SZ) was greater than that of the base material, which was only affected slightly by the travel speed.The tensile strength of the joint decreased with increasing travel speed and the maximal strength efficiency reached 99%.

Microstructure and mechanical properties of AA6063 aluminum alloy wire fabricated by friction stir back extrusion(FSBE) process

In the present work,the friction stir back extrusion(FSBE)process was used as a novel method for the fabrication of AA6063 aluminum alloy wire.Scanning electron microscopy(SEM)equipped with energy dispersive spectroscopy(EDS),tensile and hardness tests were performed.The FSBE via the rotational speed of 475 r/min resulted in fine equiaxed grains,and the mean grain size decreased from 179.0μm to 15.5μm due to the occurrence of dynamic recrystallization(DRX).Heat generated by the FSBE changed the size and volume fraction of the Mg2Si precipitated particles.The minimum particle size and maximum volume fraction obtained in the sample were processed by rotational speeds of 475 and 600 r/min,respectively.The 475-r/min sample had the maximum hardness value due to having the lowest grain size(i.e.,15.5μm)and the presence of many fine Mg2Si precipitates in the aluminum matrix.With increasing rotational speed up to 600 r/min,the hardness decreased,owing to the growth of both grains and precipitates.The FSBE process with a rotational speed of 475 r/min increased the tensile strength(from 150 to 209 MPa)and ductility(from 21.0%to 30.2%)simultaneously.

Microstructure and mechanical properties of Al-Si-Ni coating on Cu-Cr substrate prepared by multi-permeation and friction stir processing

The surface of copper-chromium alloy was processed by Al-Si-Ni multi-permeation and friction stir processing,and the microstructure and mechanical properties of the surface layer were tested by scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),microhardness tester and friction testing machine.The results show that Al,Si and Ni elements are fully permeated into the surface of copper-chromium alloy after multielement co-infiltration and friction stir processing.In the observation of the microstructures,we found that the reticular structure is fragmented and distributed in the stir zone region.Microstructure becomes finer and grains refinement.The micro hardness of the copper-chromium alloy increased to 129 HV,44.9%higher than that of the original matrix.The main reasons of microhardness enhancement are solid solution strengthening,fine grains strengthening and dispersion strengthening.The friction test results show that the friction coefficient is basically stable at 0.69 and the wear mass is only 0.0017 g after 10 min of friction test.The improvement of wear resistance was attributed to the increase of microhardness of the alloy surface.

Microstructure Evolution and Mechanical Properties of Friction Stir Welded Al-Cu-Li Alloy

The investigation concentrates on friction stir welded(FSW)Al-Cu-Li alloy concerning its local microstructural evolution and mechanical properties.The grain features were characterized by electron back scattered diffraction(EBSD)technology,while precipitate characterization was conducted by using transmission electron microscopy(TEM)aligned along[011]Al and[001]Al zone axes.The mechanical properties are evaluated through micro-hardness and tensile testing.It can be found that nugget zones exhibit finely equiaxed grains evolved through complete dynamic recrystallization(DRX),primarily occurring in continuous dynamic recrystallization(CDRX)and discontinuous dynamic recrystallization(DDRX).In the thermal-mechanically affected zone(TMAZ),numerous sub-structured grains,exhibiting an elongated morphology,were created due to partial DRX,signifying the dominance of CDRX,DDRX,and geometric dynamic recrystallization(GDRX)in this region.T_(1)completely dissolves in the nugget zone(NZ)leading to the formation of Guinier-Preston zones and increase ofδ′,β′and S′.Conversely,T_(1)partially solubilizes in TMAZ,the lowest hardness zone(LHZ)and heat affected zone(HAZ),and the residual T_(1)undergoes marked coarsening,revealing various T_(1)variants.The solubilization and coarsening of T_(1)are primary contributors to the degradation of hardness and strength.θ′primarily dissolves and coarsens in NZ and TMAZ,whilst this precipitate largely coarsens in HAZ and LHZ.σ,TB,grain boundary phases(GBPs)and precipitate-free zone(PFZ)are newly generated during FSW.σexists in the TMAZ,LHZ and HAZ,whereas TB nucleates in NZ.GBPs and PFZ mostly develop in LHZ and HAZ,which can cause strain localization during tensile deformation,potentially leading to LHZ joint fracture.

Applicability of unique scarf joint configuration in friction stir welding of AA6061-T6:Analysis of torque,force,microstructure and mechanical properties

The present research introduces a unique concept of scarf joint technique in friction stir welding(FSW) of aluminum alloy AA 6061-T6 plates and an investigation on weld quality.A new joint configuration with two distinct scarf angles(75°and 60°) was considered in this study.The various aspects of welding were compared with contemporary simple square butt(SSB) joint configuration.Welding was carried out at a constant tool rotation speed(TRS),tool traverse speed(TTS) and tool tilt angle of 1100 rpm,2 mm/s and2°,respectively.The results are analyzed in terms of force and torque distribution,microstructure,macrostructure,and mechanical property perspective for different joint configurations.The study reveals the minimum amount of force and torque at 60°scarf angle joint configuration compared to that of square butt joint configuration.Macro study shows that all the joints were defect-free,and a prominent onion ring was present in the lower portion of the weld nugget(WN).Fine equiaxed grains with a minimum average grain size diameter of 6.82 μm were obtained in the WN of scarf joint configuration(SJC).The maximum ultimate tensile strength(UTS) and maximum average NZ hardness of 267 MPa and83.82 HV0.1were obtained in SJC3 at a scarf angle of 60°.It has been observed from the investigation that the joint efficiency increases from 72.5%(SSB) to 86%(SJC3) at a 60° scarf angle.This unique characteristic may lay an impetus on probable joint strength enhancement technique without increasing the production cost.

Effect of Ti on microstructure and properties of electromagnetic stirred Al-18wt.%Mg_(2)Si alloy

By adding different amounts of Ti into the electromagnetic stirred Al-18wt.%Mg_(2)Si alloy,the effect of Ti element on the microstructure and mechanical properties of the alloy was studied.The experimental results show that the microstructure is refined after modification with Ti,which is related to the heterogeneous nucleation of TiAl_(3) particles on theα-Al matrix.With the increase of Ti content and holding time after stirring,the primary Mg_(2)Si phase is refined firstly and then coarsened,and correspondingly,the mechanical properties of the alloy show a trend of increasing at first and then decreasing.When the addition of Ti is 0.5wt.%and the holding time is about 20 min,the refinement effect of primary Mg_(2)Si phase is the most significant and the mechanical properties of the alloy are optimal.