Cryogenic springback of 2219-W aluminum alloy sheet through V-shaped bending

A V-shaped bending device was established to evaluate the effects of temperature and bending fillet radius on springback behavior of 2219-W aluminum alloy at cryogenic temperatures.The cryogenic springback mechanism was elucidated through mechanical analyses and numerical simulations.The results indicated that the springback angle at cryogenic temperatures was greater than that at room temperature.The springback angle increased further as the temperature returned to ambient conditions,attributed to the combined effects of the “dual enhancement effect” and thermal expansion.Notably,a critical fillet radius made the springback angle zero for 90° V-shaped bending.The critical fillet radius at cryogenic temperatures was smaller than that at room temperature,owing to the influence of temperature variations on the bending moment ratio between the forward bending section at the fillet and the reverse bending section of the straight arm.

Segregation in fusion weld of 2219 aluminum alloy and its influence on mechanical properties of weld

Three kinds of welds were made using low frequency pulse current variable polarity tungsten inter gas （LPVPTIG） with argon shielding, direct current TIG （DCTIG） with helium shielding and high frequency pulse current variable polarity TIG （HPVPTIG） with argon shielding, respectively. It was found that macrosegregation bands with large amount of thick continuous eutectics and microporosities formed in the LPVPTIG weld due to the fluctuation of the pulse varied heat input. Only microsegregation existed in the DCTIG weld and HPVPTIG weld. However,the HPVPTIG weld had lower extent of Cu microsegregation since its welding speed was slower. The tensile results indicated that the mechanical properties of the weld decreased with the increase of the segregation extent of Cu and porosities, and LPVPTIG weld had lower tensile properties in the longitudinal direction than those in the transverse direction due to the macrosegregation bands.

Effects of weld reinforcement on tensile behavior and mechanical properties of 2219-T87 aluminum alloy TIG welded joints

Tungsten inert gas （TIG） welded joints for 2219-T87 aluminum alloy are often used in the fuel tanks of large launch vehicles. Because of the massive loads these vehicles carry, dealing with weld reinforcement on TIG joints represents an important issue in their manufacturing and strength evaluation. Experimental and numerical simulation methods were used to investigate the effects of weld toe shape and weld toe position on the tensile behavior and mechanical properties of these joints. The simulation results indicated that the relative difference in elongation could be as large as 96.9% caused by the difference in weld toe shape. The joints with weld toes located in the weld metal or in the partially melted zone （PMZ） exhibited larger elongation than joints with weld toes located at the juncture of the weld metal and the PMZ.

Fracture behavior of double-pass TIG welded 2219-T8 aluminum alloy joints under transverse tensile test

2219-T8 aluminum alloys were butt welded by the double-pass tungsten inert gas （TIG） arc welding process. The transverse tensile test of the joint showed that the fracture mainly occurred in the partially melted zone （PMZ）. Effects of the PMZ on the fracture behavior were systematically studied. Continuous intergranular eutectics were observed in the PMZ close to the fusion line. Away from the fusion line, the intergranular eutectics in the PMZ became discontinuous. The fracture morphology and the microhardness distribution of the joint showed that the PMZ was gradient material with different mechanical properties, which strongly affected the fracture process. It was observed that the crack initiated in the PMZ near the front weld toe, and propagated in the PMZ away from the fusion line. Then, the crack tip was blunt when it propagated into the PMZ with higher plasticity. Finally, the rest part of the joint was shear fractured.

Effects of weld penetration on tensile properties of 2219 aluminum alloy TIG-welded joints

Numerical simulation and experimental methods were used to investigate the effects of weld penetration on tensile properties of 2219 aluminum alloy tungsten inert gas(TIG)welded joints.The results show that when other geometric parameters are consistent,within a certain range,the deeper the weld penetration of the capping weld is,the lower the tensile strength of the j oint is.The deeper weld penetration of the capping weld can cause the more concentrated stress at the weld toe and the joint is more likely to crack accordingly.Based on necessary assumptions,a model for analyzing the mathematical relation between the weld penetration of the capping weld and the tensile strength of the joint was proposed to validate the experimental results. The decrease of weld penetration of capping weld can be controlled by decreasing welding current,helium content or increasing welding voltage.

Constitutive modeling and springback prediction of stress relaxation age forming of pre-deformed 2219 aluminum alloy

Stress relaxation ageing behavior of pre-deformed AA2219 is studied through stress relaxation age experiments and finite element(FE) simulation. The results show that the stress can promote the process of ageing precipitation, and shorten the time to reach the peak strength. Meanwhile,the residual stress and yield strength increase along with the increase in the initial stress. Based on microstructure evolution and ageing strengthening theory,a unified constitutive model is established and incorporated into the FE simulation model through a user subroutine. It is found that the relative error of the radius is 3.6% compared with the experimental result and the springback is 16.8%. This indicates that the proposed stress relaxation ageing constitutive model provides a good prediction on the springback of such stiffened panel during its ageing process.

Numerical simulation of thermal field of FSW 2219 aluminum alloy thick plate

To investigate the influence of temperature field of friction stir welding(FSW)2219 aluminum alloy thick plate,and to achieve effective prediction of temperature field,the authors establish a three-dimensional numerical simulation model of FSW 18 mm thick 2219 aluminum alloy based on ABAQUS/CEL,considering the morphological characteristics of the tool pin.The simulations of plunging,dwelling,and welding stages are achieved.The distribution of temperature and temperature cycle curve of characteristic points in welding process are obtained.The validity of the simulation results is verified by experiments.The influence of the tool-rotational speed and welding speed on temperature field is explored.The work lays a foundation for the prediction and control of temperature field in FSW medium thickness 2219 aluminum alloy,and provides reference for selection of welding parameters to ensure high quality welding of fuel tank of heavy-lift rocket.

Electron beam welding of SiCp/2024 and 2219 aluminum alloy

SiCp/2024 matrix composites reinforced with SiC particles and 2219 aluminum alloy were joined via centered electron beam welding and deflection beam welding,respectively,and the microstructures and mechanical properties of these joints were investigated.The results revealed that SiC particle segregation was more likely during centered electron beam welding(than during deflection beam welding),and strong interface reactions led to the formation of many Al4C3 brittle intermetallic compounds.Moreover,the tensile strength of the joints was 104 MPa.The interface reaction was restrained via deflection electron beam welding,and only a few Al4C3 intermetallic compounds formed at the top of the joint and heat affected zone of SiCp/Al.Quasi-cleavage fracture occurred at the interface reaction layer of the base metal.Both methods yielded a hardness transition zone near the SiCp/2024 fusion zone,and the brittle intermetallic Al4C3compounds formed in this zone resulted in high hardness.

Microstructural evolution and its effect on mechanical properties in different regions of 2219-C10S aluminum alloy TIG-welded joint

Microstructural evolution and its effect on mechanical properties in different regions of 2219-C10S aluminum alloy tungsten inert gas(TIG)welded joint were analyzed in detail.In weld zone(WZ),α+θeutectic structure formed at grain boundaries with no precipitates inside the grains.In partially melted zone(PMZ),symbiotic eutectic or divorced eutectic formed at grain boundaries and needle-likeθ′phases appeared in the secondary heated zone.In over aged zone(OAZ),the coarsening and dissolution ofθ′phases occurred and mostθ′phases transformed intoθphases.In general heat affected zone(HAZ),θ′phases coarsened.Factors such as the strengthening phases,the grain size,the Cu content in matrix and the dislocation density can affect the mechanical properties in different regions of the joint.Moreover,a model describing the relationship between mechanical properties of the material and the volume fraction of precipitates,the average diameter of precipitates and the concentration of soluble elements was proposed.

Long-term stress relaxation behaviors and mechanisms of 2219 Al-Cu alloy under various temperatures and initial stresses

Large 2219 Al-Cu alloy aerospace integral components suffer from long-term stress relaxation aging(SRA)due to complex temperature and stress loads during aging treatment/forming and service process,which makes it difficult to ensure their appropriate residual stress and excellent mechanical and service prop-erties.However,the research is limited to a thorough understanding of macroscopic and microscopic features and underlying mechanisms of the long-term SRA under multivariable aging conditions.There-fore,this study investigated macroscopic and microscopic features of long-term SRA under different tem-peratures(120 ℃ to 190 ℃),initial stress levels(100 MPa to 250 MPa)and durations(0 h to 50 h)through stress relaxation curves,metallographic traits,Vickers hardness,tensile performance,disloca-tions and phases of precipitation.On the basis of experimental outcomes,the comprehensive mecha-nisms beneath SRA were unraveled through dislocation theory,multiphase strengthening mechanisms and thermodynamics,where the interplays of stress relaxation behavior with age-hardening response were taken into consideration.The results showed elevations in the rate of stress reduction as the tem-perature and initial stress rose.At an initial stress greater than the yield stress of alloy,a marked in-crease in stress relaxation was found,and the mechanisms transform from the intragranular motion of dislocations and diffusion of grain boundaries to the intragranular and intergranular motion of disloca-tions and migration of grain boundaries.The stress reduction rate rose sharply when the temperature exceeded 175 ℃,and the dislocation movement mechanisms transform from gliding to climbing of dislo-cations.Stress relaxation is in nature progressive transformation of strain from elastic into a permanently inelastic state via the motion of dislocations,leading to the decrease of movable dislocations and the increase of immovable dislocations with more stable configurations.The age hardening is mainly deter-mined by precipitation strengthening,supplementarily by dislocation strengthening,and obvious stress orientation effect(SOE)of G.P.zones and θ"phases degenerates strengthening effect.The interplay be-tween stress relaxation behavior and age-hardening response influences the thermal-mechanical coupling SRA of 2219 Al-Cu alloy,which depends fundamentally on the motion of dislocations and their interplay with precipitated phases.This is a thermal activation process concerning the interplay between internal(age-hardening resistance)stress and external(initial)stress.The initial energy of elastic strain offers Gibbs free energy as the SRA driver,and a steady state of stress relaxation is attained with the lowest energy of elastic strain.These findings provide valuable insights into exploring innovative aging treat-ment/forming for optimizing residual stress,mechanical performance and service property in a synergistic manner.

Effect of blank quenching on shear spinning forming precision of 2219 aluminum alloy complex thin-walled components

The quenching-spinning(Q-S)process,i.e.,shear spinning after blank quenching,has been increasingly utilized to form 2219 aluminum alloy complex thin-walled components.However,the changes in material property,shape and stress of the blanks after quenching will affect the spin-ning forming precision.In this study,the rules and mechanisms of these effects are investigated based on a combined finite element(FE)model including blank quenching and component spinning process.The results indicate that the increase of material strength and the existence of distortion of the quenched blank lead to a notable increase in the non-uniformity of the circumferential compres-sive stress in the spinning area and the increase of the flange swing height during spinning.These changes result in an increase in the wall thickness and component-mandrel gap of the components.The quenching residual stress has little effect on wall thickness and roundness but can noticeably reduce the component-mandrel gap.This is because that the existence of quenching residual stress of the blank can lead to the decrease of the maximum circumferential compressive stress of the workpiece in spinning and an obvious drop in the maximum compressive stress after reaching the stress peak.Quenching distortion is the main factor affecting the roundness.Moreover,the opti-mized installation way of the blank for spinning is obtained.

Microstructural Evolution and Softening Behavior of Simulated Heat-Affected Zone in 2219 Aluminum Alloy

The effect of peak temperature （Tp） at 200, 300, 400, 500 and 550 ℃ on the microstructural evolution and softening behavior of the simulated heat-affected zone （HAZ） was studied in the 2219-T87 alloy by electron-backscatter diffraction, transmission electron microscopy, X-ray diffraction, micro-hardness and micro-tensile tests. The results showed that the grain size in the HAZs at 200-500 ℃ was comparable, but the number density of the strengthening precipitates （GP zones/θ′） decreased with increasing Tp. At a Tp of 550 ℃, the grain size significantly decreased and the distribution of the misorientation angles corresponded to the MacKenzie distribution. The GP zones/θ′ phase coarsened and translated into θ phases at Tp values in the range of 200-400 ℃. Increasing the Tp to 500 ℃ and above, some θ′ phases translated into θ phases and others dissolved into the α-Al matrix which led to an increase in the solid solution strengthening. The reduction of the number density of the GP zones/θ′ was responsible for the softening behavior.

Microstructure and mechanical properties of 2219 aluminum alloy VPTIG welds during cyclic thermal treatment

In this study,the effect of the cyclic thermal treatment(CTT) on the microstructure and mechanical properties of the 2219 Al alloy welds fabricated using variable polarity tungsten inert gas(VPTIG) arc welding method were investigated by optical microscope(OM),transmission electron microscope(TEM),and low-temperature tensile tests,with emphasis on precipitation evolution and property variation in different areas of the joint.Measurement of the microhardness profile across the weld reveals that there are maximum and minimum hardness values in the heat-affected zone(HAZ) adjacent to the fusion boundary(FB).It is found that the maximum hardness value increases with the temperature cycles of the cyclic thermal treatment due to the formation of GuinierPreston(GP) zones,while the microhardness at other positions remains unchanged.Experimental results show that the CCT results in an increase in the yield strength,but a decrease in the ductility of the weld joint.

Correlation Between Microstructure and Mechanical Properties of 2219-T8 Aluminum Alloy Joints by VPTIG Welding

In this study, 2219-T87 aluminum alloys were butt welded by the double-pass tungsten inert gas arc welding process. And the softening behavior of fusion zone（FZ） and heat-affected zone（HAZ） was evaluated with the analysis of welding temperature field, grain size, alloying element distribution and precipitates evolution. Results show that the two FZs are almost the weakest regions in the joint, where the microhardness value is 76 and 78 HV, respectively. Microhardness of the HAZ generally grows along with increasing distance from fusion line except a valley value at the distance of about 4.5 mm. The mean grain size of two FZs is about 74.4 and 79.2 lm, whereas 41.5, 44.9 and 43.4 lm for the two measured HAZs and base metal（BM）, respectively. There is about 60.4% and 54.2% Cu consumed in the coarse whitish particles of FZs that have little strengthening effect, while the percentage is about 24.6% of BM that is almost the same as HAZ. A large number of strengthening phases h0 distribute dispersively in BM, whereas hardly any precipitates exist in FZ and HAZ adjacent to FZ. So the coarsening of grain size, reduction and segregation of alloying element content, and the precipitate evolution are regarded as the main causes of softening in FZ, while the precipitate evolution is the main factor of softening in HAZ.