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Variable polarity plasma arc welding (VPPAW) can be used for the excellent welding of 5A06 aluminum alloy, which is promising for aerospace applications due to its excellent welding performance and small welding deformation. In this paper, the corrosion behavior of the welding specimens was studied by a metallographic microscope, scanning electron microscope, energy dispersive spectrometer, x-ray diffractometer, and electrochemical workstation. The VPPA welded joint metallographic specimens were subjected to salt spray corrosion tests for 24, 54, 84, 114 and 144 h. The results showed that the heat-affected zone (HAZ) is more sensitive to corrosion than the weld metal (WM) and the base metal (BM), which resulted from the existence and distribution of β(Al3Mg2) and Al6(FeMn) phases in welded joints. The corrosion resistance of VPPA welded joints is WM > BM > HAZ. However, salt spray corrosion increased the corrosion sensitivity of the WM. With the increase of salt spray corrosion time, the WM corrosion tendency raised, and the corrosion resistance of WM became lower than the BM. The corrosion rate curve showed an increasing trend at first and then decreased with the increase of corrosion time, and the corrosion rate reached the highest at 84 h. [ABSTRACT FROM AUTHOR]

In this research, the temperature field characteristics and melt flow behaviors of 5A06/6061 aluminum alloy lock-butt joint during the electron beam welding (EBW) process are investigated by numerical simulation involving heat transfer and flow of fluid. The calculated mesh model of the lock-butt joint is established with the computational domain divided into three phases. The rotating Gauss heat source is applied to simulate the electron beam energy loaded on the base metal during the welding process. Immediately, not only the temperature filed distributions on the surface and different sections of the molten pool are analyzed carefully, but the flow behaviors of the liquid metal in the molten pool are studied in detail. The results demonstrate that the asymmetric distribution of the temperature field, keyhole, and molten pool morphology exist constantly during the welding process. Besides, there are asymmetric metal flows on both sides of the molten pool and obvious vortex metal flows near the rear and the surface of the molten pool. The melt flow on the keyhole wall represents diversity including the surrounding, downstream, and upstream flow. Moreover, the corresponding experiment is conducted to verify the accuracy of the established model and the simulation results are in good agreement with the experimental results in this work. [ABSTRACT FROM AUTHOR]

The laser welding technology of ultra-thick plates has been widely applied in many crucial engineering structures, where its safety and stability still suffer from the residual stress brought by the welding temperature. In this work, experimental and numerical studies are carried out to reveal the evolution and distribution of the residual stress. A 5A06 aluminum alloy plate with 30 mm thickness is used to conduct the laser welding experiment, and the short-wavelength X-ray diffractometer (SWXRD) is employed to measure the residual stress. Furthermore, a multi-pass laser welding numerical model is developed to predict the residual stress during the welding process. The simulation results of the weld pool geometry and residual stress agree well with the experimental data, which gives a good validation of the numerical model. Based on the proposed numerical model, the influence of the welding parameters, including inter-pass cooling time and welding rate are also investigated. It is discovered that the reduction of the inter-pass cooling time results in weakness effect of the temperature gradient, which hinders the generation of plastic deformation and leads to a lower residual stress value. Meanwhile, the simulation results also show that the increase in welding rate promotes the generation of thermal stress, which brings a higher residual stress value appeared in the structure.

The hot press bend process of the 5A06 aluminum alloy high-stiffener integral panels was studied by FEM simulations and experiments. The high-temperature deformation behaviors and microstructures were tested by the high-temperature uniaxial tensile tests and the electron backscatter diffraction (EBSD), respectively. A set of physically-based constitutive equations and its VUMAT user subroutine, including dislocation density, grain size, and deformation damage, were established. The effects of forming parameters and blank size on the forming quality of the high-stiffener integral panel were studied. The main typical defects were the surface groove, side face curvature and inclination, springback, and wrinkle of the stiffener. The high-stiffener integral panels should be bent above 350 °C and kept for more than 20 min under a pressure of 8 MPa. [ABSTRACT FROM AUTHOR]

5A06 aluminum alloy bar was brazed by temperature gradient transient liquid phase diffusion welding (TG-TLP). The effects of brazing temperature on the microstructure and the tensile strength of the brazing joints were investigated. Three typical brazing filler alloys (1# Al-20Cu-6Si-2Ni, 2# Al-10Cu-10Si-3Mg-1Ga, and 3# Al-6Cu-10Si-2Mg-10Zn) were prepared by smelting, and TG-TLP diffusion bonding was carried out at different brazing temperatures (550 °C~590 °C). The results show that with the increase in brazing temperature, the oxide films at the brazing junction are easier to be broken and dispersed, but the oxidation extent will also increase. The oxidation products enriched were mainly Al2O3 and SiO2 at the brazing junction. There are different optimal brazing temperatures corresponding to the different filler alloys. For 1#, the optimal temperature is 570 °C; for 2# is 580 °C; for 3# is 580 °C. For 1# brazing joints, the maximum tensile strength was 113 MPa, and for 2# was 122.4 MPa. Under the experimental conditions of this study, the maximum tensile strength of the TG-TLP joint is 147.4 MPa of 3# brazing sample (at 580 °C), which has increased by 30% and 20% compared to 1# and 2# respectively. The nickel-rich phase at the interface (of 1# brazing filler) could form a brittle fracture, which was unfavorable for interface bonding. For TG-TLP brazing of 5A06, the filler alloy with high Al:Cu ratio (12:1 wt.%) needs a sufficient temperature gradient to exert the film-breaking effect, while the filler alloy with low Al:Cu ratio (3.6:1 wt.%) needs to accurately control its brazing temperature to avoid excessive oxidation. There are many research gaps in the influence of brazing material composition and brazing temperature on the microstructure and mechanical properties of 5A06 aluminum alloy TG-TLP joints. The research results can provide a theoretical basis for formulating the TG-TLP brazing specification of 5A06 aluminum alloy. [ABSTRACT FROM AUTHOR]

This paper studies the grain refinement mechanisms of 5A06 aluminum alloy sheets in cold rotary forging (CRF). The results show that the grains are clearly refined from 25.1 µm to 11.8 µm during the CRF process. The grain refinement mechanism can be divided into two modes: (1) The grains with a small Schmid factor (SF) are activated by multi-slip systems, and dense dislocations are segregated along the boundaries of interior regions with different slip systems, which results in a rapidly increasing strain localization along these boundaries. Since the strain localization restrains the coordinate slip deformation between different interior regions, the grains are directly separated into several finer grains. (2) The grains with a large SF are primarily activated by a single slip system, and the dislocation migrates smoothly along most microband boundaries. Then, a more severe lattice rotation causes a transformation to a hard orientation and multi-slip system activation, which contributes to an increase in the rapid misorientation across microband boundaries and thus promotes significant SF grain refinement. [ABSTRACT FROM AUTHOR]

For the purpose of eliminating the annular welding seams in welding structures with differential thickness, a hydroforming method using a circular 5A06 aluminum alloy plate with a radial differential thickness in coupling with a flexible polyurethane auxiliary plate was proposed to form an integrated semi-ellipsoid shell. The circular 5A06 aluminum alloy plate had a smaller in the middle and a larger thickness in the periphery. In the forming process of such aluminum alloy plates, concentrated deformation and fracture might have occurred in the thin zone. According to the size of the target specimen, the testing plates with two types of thickness ratios were obtained by mechanical processing. Furthermore, the thickness and strain of the drawn specimens with different thickness ratios were analyzed under different hydraulic pressure by means of deep drawing experiments. Compared to the conventional deep drawing, the formability of 5A06 aluminum alloy plates with differential thickness could be effectively improved by hydroforming. The integrated semi-ellipsoid shells with the thickness ratios of 2/3 and 1/2 were obtained under the hydraulic pressure of 10 MPa with maximum thinning ratios of 8.5% and 10.9%, respectively. In a word, the increase in hydraulic pressure could effectively reduce the maximum thinning ratio in the thin zone, and improve the thickness distribution uniformity. [ABSTRACT FROM AUTHOR]

In order to avoid softening and improve the mechanical properties of the aluminum alloy welded joints,the butt test of 5A06 aluminum alloy was carried out with FSW,and the welded joints were processed into metallographic samples and tensile samples of a certain size under the conditions of a rotating speed of 1 200 r/min and a welding speed of 150 mm/min,the effect of deep cryogenic treatment (DCT) time on microstructure and mechanical properties of friction-stir-welded joints of 5A06 aluminum alloy was investigated.The experiments were carried out by microstructure observation test,micro-hardness test and tensile test to characterize and analyze the joint organization and mechanical properties.The experiment results show that DCT can refine the grain and promote the precipitation of the second phase,thus the mechanical properties of the joints are improved.The tensile strength and elongation of the joints can reach 385.3 MPa and 17.2% respectively,which are increased by 7.4% and 23.7%,respectively after 12 h DCT compared with the joints without DCT.Therefore,DCT can effectively improve the mechanical properties of aluminum alloy joints and provide theoretical and technical basis for its application.

In order to improve the comprehensive mechanical properties of the welded joints of the 5A06 aluminum alloy, friction stir welded (FSW) joints were subjected to deep cryogenic treatment (DCT). The microstructure and mechanical properties were characterised using metallographic microscopy, x-ray diffractometer (XRD), energy spectrometer, microhardness tests, and tensile tests. The experimental results show that DCT refines the structure significantly due to the large temperature difference. This refinement results from an increase in Mg atoms within the α -Al solid solution through the precipitation of Al atoms, forming the Al _3 Mg _2 phase. This enhancement in plasticity is achieved through dispersion distribution. Moreover, as the treatment time of DCT increases, the mechanical properties of the welded joint also improve significantly. The microhardness of the welding joint peaked at DCT3h, rising from 78.8 HV at DCT0h to 87.2 HV at DCT3h. Meanwhile, the tensile strength of the joint reached its maximum at DCT12h, rising from 358.7 MPa at DC0h to 385.3 MPa at DCT12h, representing a 7.4% increase. These experimental results underscore the significant impact of DCT on improving the welded joints.

Aluminum alloy tubes were prepared by tube spinning. The intergranular and electrochemical corrosion tests were used to investigate the intergranular corrosion behavior of the 5A06 aluminum alloy blank sample and the spinning sample. Results showed that the intergranular corrosion resistance of the spinning sample was higher than that of the blank sample. In addition, the electrochemical corrosion resistance of the spinning sample was higher than that of the blank sample. The EDS maps indicated a uniform element distribution pattern of aluminum and magnesium. Moreover, the phase composition and lattice constant of the samples were obtained by XRD analysis. The differences in microstructure between the aluminum alloy subjected to the spinning process and the untreated aluminum alloy were determined by EBSD. The differences were mainly attributed to the complex interactions among grain size, dislocations and grain boundaries. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Hebei University of Science & Technology is the property of Hebei University of Science & Technology, Journal of Hebei University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, laser-arc hybrid welding of 5A06 aluminum alloys was performed firstly. To improve the surface quality of welded joints, ultrasonic peening (UP) process was employed. The influence of different peening needle velocities on surface microstructure and properties was investigated. The results indicated that UP produced protrusions and grooves on treated surface of welded joints. EBSD analysis showed that grains in UP-treated surface layers was refined from 100 to 50 μm. Improved dislocation structure was observed via TEM analysis. Increasement in full width at half maximum (FMHW) and Bragg angle of diffraction peaks in XRD analysis further demonstrated the formation of fine grains. The surface microhardness increased by 38.9% from 92.6 to 132 HV due to the work hardening effects. In addition, UP-treated welded joints possessed better wear resistance. After UP process, a 50% decrease in wear rate was obtained. The wear mechanism changed from adhesive to abrasive wear for the UP-treated joints. Besides, the possibility of corrosion initiation and the corrosion rate of UP-treated joints were lower than those of non-treated joints implying better corrosion resistance.

5A06 aluminum alloy bar was brazed by temperature gradient transient liquid phase diffusion welding (TG-TLP). The effects of brazing temperature on the microstructure and the tensile strength of the brazing joints were investigated. Three typical brazing filler alloys (1# Al-20Cu-6Si-2Ni, 2# Al-10Cu-10Si-3Mg-1Ga, and 3# Al-6Cu-10Si-2Mg-10Zn) were prepared by smelting, and TG-TLP diffusion bonding was carried out at different brazing temperatures (550 °C~590 °C). The results show that with the increase in brazing temperature, the oxide films at the brazing junction are easier to be broken and dispersed, but the oxidation extent will also increase. The oxidation products enriched were mainly Al2O3 and SiO2 at the brazing junction. There are different optimal brazing temperatures corresponding to the different filler alloys. For 1#, the optimal temperature is 570 °C; for 2# is 580 °C; for 3# is 580 °C. For 1# brazing joints, the maximum tensile strength was 113 MPa, and for 2# was 122.4 MPa. Under the experimental conditions of this study, the maximum tensile strength of the TG-TLP joint is 147.4 MPa of 3# brazing sample (at 580 °C), which has increased by 30% and 20% compared to 1# and 2# respectively. The nickel-rich phase at the interface (of 1# brazing filler) could form a brittle fracture, which was unfavorable for interface bonding. For TG-TLP brazing of 5A06, the filler alloy with high Al:Cu ratio (12:1 wt.%) needs a sufficient temperature gradient to exert the film-breaking effect, while the filler alloy with low Al:Cu ratio (3.6:1 wt.%) needs to accurately control its brazing temperature to avoid excessive oxidation. There are many research gaps in the influence of brazing material composition and brazing temperature on the microstructure and mechanical properties of 5A06 aluminum alloy TG-TLP joints. The research results can provide a theoretical basis for formulating the TG-TLP brazing specification of 5A06 aluminum alloy.

In this paper, the numerical simulation of the temperature field and welding angular distortion of a 6mm-thick 5A06 aluminum alloy plate was performed by application of the ABAQUS 2018 finite element analysis software. A 3D thermo-mechanical model of the plate under study with account of heat transfer in the arc motion direction was established. The temperature field distribution and welding-induced angular distortion in the welded structure obtained by the simulation were analyzed to minimize the production cost and improve the production efficiency. By analyzing the magnitude and distribution of residual stresses in the welded structure, selecting a reasonable welding process, and optimizing the design to reduce and control the residual stress, the aluminum alloy welded structure can be effectively manufactured. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin University of Science & Technology is the property of Journal of Harbin University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The 5A06 aluminum alloy butt joint is fabricated by laser-metal inert gas (MIG) hybrid welding in this investigation. The macro morphology and porosity of welded joints under different heat input are observed by optical microscope. The effect of the laser, MIG, and hybrid heat input on macro morphology and porosity of welded joint is investigated. Furthermore, the force condition inside the laser-MIG hybrid welding pool is analyzed to explain the influence mechanism of heat input on macro morphology and porosity in theory. It is found that the cross-section area of weld seam (WS) is increased with the welding heat input. The porosity of the full-penetration WS is smaller than the partial-penetration WS owing to the different flow characteristic of molten pool. The higher MIG heat input is beneficial to reduce the porosity. It is illustrated that the welded joint with a lower porosity is expected to be obtained under the energy ratio coefficient of 0.5. [ABSTRACT FROM AUTHOR]

To shorten the semisolid billet process and reduce its cost, the effects of isothermal temperature and soaking time on the microstructural evolution and coarsening rate during directly heating room temperature hot-rolled 5A06 aluminum alloy to semisolid temperature were investigated. Samples cut from the hot-rolled plates were heated to semisolid temperatures ranging from 580 to 620 °C, and soaking for 5-30 min. The microstructure of samples was characterized by optical microscopy, scanning electron microscopy with energy-dispersive x-ray spectroscopy, and Image-Pro Plus software. The results showed that the microstructure contained ellipsoidal solid grains with the quantitative parameters of the average grain size of 143 µm and averaged shape factor of 0.55 under an optimal condition of 615 °C for 20 min. Recrystallization occurred within 5 min of holding time, increasing temperature can promote recrystallization, which is beneficial to spheroidization of solid phase, and it will also accelerate melting and the growth of solid particles. Extending soaking time, the liquid phase increased gradually and the change of solid particles was complicated. Abnormal accumulation of liquid phase was found, which will lead to the formation of irregular structure. The reasonable coarsening rate constants ranged from 1319 to 3454 μm3 s−1 under the desired treatment parameters. The segregation of Mg occurred at the grain boundaries, as well as around the inclusions within the grains. [ABSTRACT FROM AUTHOR]

The residual stresses and deformation, in terms of the thermoelastoplastic theory, were simulated with the finite element method using ANSYS 13.0 software for a 5A06 aluminum alloy plate after welding. The butt joint thickness of the plate was 6 mm. A 3D thermomechanical model of the plate was constructed. The dimensions and distribution of residual stresses in the welded structure should be analyzed after simulation. Appropriate welding technologies were chosen to control welding residual stresses and deformation. The efficient production of an aluminum alloy for the welded structures will be provided. [ABSTRACT FROM AUTHOR]

Wire and arc additive manufacturing(WAAM) was investigated by tungsten inert gas arc welding method(TIG), in which φ1.2mm filler wire of aluminum alloy 5A06(Al-6Mg-Mn-Si) was selected as deposition metal. The prototyping process was conducted by a TIG power source(working in AC mode) manipulated by a four-axis linkage CNC machine. Backplate preheating temperature and arc current on deposited morphologies of single layer and multi-layer were researched. The microstructure was observed and the sample tensile strength was tested. For single layer, a criterion that describes the correlation between backplate preheating temperature and arc peak current, of which both contribute to the smoothening of the deposited layer. The results show that the layer height drops sharply from the first layer of 3.4mm and keeps at 1.7mm after the 8th layer. Fine dendrite grain and equiaxed grain are found inside a layer and coarsest columnar dendrite structure at layer boundary zone; whereas the microstructure of top region of the deposited sample changes from fine dendrite grain to equiaxed grain that turns to be the finest structure. Mechanical property of the deposited sample is isotropic, in which the tensile strength is approximately 295MPa with the elongation around 36%.

Molten pool uniformity is a prerequisite for wire and arc additive manufacture to achieve a uniform surface appearance. The thermal boundary is a key indicator to evaluate the thermodynamic state of the molten pool. This paper focuses on thermal analysis through finite element simulation and characterizes the thermal evolution of a molten pool during bottom-up deposition. The peak temperature of the substrate plate increases from 375.7 °C to 623.1 °C when peak current increases from 120 A to 180 A. The temperature gradient decreases from 40 °C/mm to 30 °C/mm. Weld speed increases from 0.15 m/min to 0.25 m/min; the temperature gradient is kept at about 30 °C/mm. Dimensionless thermal conductivity, Ge number, is proposed and defined as the criteria to estimate layer size variation. For Ip = 140 A, the average value of the Ge number is 87.7, and it shows the best numerical stability. Dimensionless thermal conductivity, Ge, is proposed and defined as the criteria to estimate the occurrence of layer size variation. Prolonging heating time and increasing cycle frequency, Ge number shows favorable stability during bottom-up deposition. The experimental results are consistent with analytical conclusions, which proves the validity of the Ge number as an indicator of deposition stability.

Experiments were carried out in this paper first to clarify the characteristics of a digging process during aluminum alloy of type 5A06 variable polarity plasma arc welding (VPPAW). A special “Blasting type” penetrating phenomenon was observed through measuring the penetrating time by electrical and optical signals. A 3D model was established to numerically investigate heat transfer, fluid flow and surface shape during the digging process. An adaptive heat source was adopted to describe heat transfer process involving deformation of the keyhole tracked by volume-of-fluid (VOF) method. The plasma arc pressure attenuated in a parabolic form as the depth of the keyhole increases. It is found that the weld pool surface becomes concave after sufficient melting of metal. The keyhole depth exhibits responsive changes, which corresponds with the different stages of welding parameters. In the late stage, the depth increase rapidly to fully penetrating state, which shows a “blasting type” penetrating process. The keyhole formation was interpreted by considering energy accumulation and mass conservation of fluid flow. The maximum velocity during digging process always occurs on the keyhole surface, where a vortex in the opposite direction appears inside the weld pool. The calculated penetrating time, keyhole size and fusion line were basically in agreement with the experimental results. [ABSTRACT FROM AUTHOR]

Friction stir double-sided butt welding was carried out for the joining of 5A06 aluminum alloys with thickness of 108 mm, and sound welds with full penetration were produced. Microstructure characterizations of the welding joint were investigated by optical microscopy, electron back-scattered diffraction and transmission electron microscopy (TEM). The results indicate that void defects are observed in shoulder-affected zone (SAZ) and grain size of equiaxed grains in SAZ and weld nugget zone (WNZ) decreases gradually along the thickness direction, while in SAZ the dislocation density is significantly lower and the sub-grain size is much larger than those in WNZ. Microhardness surveys reveal that on the upper part of the joint hardness profile presents a “V” shape and minimum hardness appears in SAZ whereas that in other regions exhibits a “W” shape and the lowest hardness value occurs in the heat-affected zone adjacent to the advancing side. The investigation of tensile properties on the FSW joint indicates the WNZ exhibited superior tensile properties compared with SAZ, and the analysis of fracture surface using the scanning electron microscopy (SEM) demonstrates that fractures in all tensile specimens are ductile fracture due to the presence of dimples with different sizes. [ABSTRACT FROM AUTHOR]

The corrosion behavior of 5A06 aluminum alloy in N 2 O 4 was investigated to explore the influence of immersion time. The XPS results confirmed the existence of corrosion products N-H and nitrate after immersion in the N 2 O 4 medium. Surface morphology analysis showed that the pitting mainly initiated around the intermetallic and their vicinity. The reason is the dissolution of the aluminum matrix around the intermetallic AlFeMn and the dealloying of magnesium in Mg 2 Si. The dissolution of the aluminum matrix near the AlFeMn precipitate and the dissolution of the AlMg precipitate lead to intergranular corrosion. Intergranular corrosion appeared after being immersed for three months and gradually developed into exfoliation corrosion. Eventually, the corrosion mechanism of aluminum alloy in the N 2 O 4 system was discussed. • Investigate the corrosion behavior of AA 5A06 in N 2 O 4 medium. • Interpret the causes and mechanisms of pitting and intergranular corrosion. • Confirm the simultaneous occurrence of chemical and electrochemical corrosion on AA 5A06 in N 2 O 4 system. [ABSTRACT FROM AUTHOR]

In-depth investigation of microstructure evolution rules and flow localization characteristics in high strain rate deformation is helpful to improve the forming limit and forming accuracy of electromagnetic forming process. In present study, split Hopkinson pressure bar tests were carried out to obtain high velocity deformation with initial strain rate ranging from 1000s -1 to 5000s -1 . Then, post-deformation samples of 5A06 alloy were analyzed with the aid of metallographic, SEM and TEM instruments. With the increase of strain rate, equiaxed α grains are elongated with an orientation perpendicular to the loading axis and the aggregated β grains become dispersively distributed along the grain boundaries. Adiabatic shear bands occur with elongated voids and band-like structures inside when the strain rate further increase to 4200s -1 . Multi-slips operate at the same time and the dislocation structure patterns change from dislocation clusters to dislocation bands and stack faults and then to grain-like structures of approximately 500 nm in size with the increase of strain rate. The absolute temperature of adiabatic shear band zone is calculated to be 442K utilizing mathematical model developed in this work, indicating that the grain-like structures could be in-situ sub-grains rather than recrystallization grains. [ABSTRACT FROM AUTHOR]

• A S-curve power of laser oscillating welding is proposed. • The grains in the welded joint with S-curve power were refined, and the mechanism of grain refinement is analyzed. • Compared with joints with constant power, the tensile strength with S-curve laser power was increased by 35.3% and could reach 99.1% of the base metal strenght. Laser oscillating welding of 5A06 aluminum alloy is widely used in industry. In order to improve the performance of Al-based welded joints and reduce welding defects, this paper details the effects of employing an S-curve laser power which is distributed along the laser oscillating path (sine wave) to improve the microstructure and mechanical properties of the joints. By applying the S-curve and an equal power condition to the 5A06 aluminum alloy, bottom butt sinusoidal path laser oscillating welding was performed. The welding appearance, microstructure and mechanical properties of the welded joints under two laser oscillating welding processes were investigated. Our results showed that laser oscillating welding using the S-curve power allows to obtain good joints when compared to the joints produced with constant power. When the linearly varying laser power of "high-low-high" applied periodically was employed, the grains in the joint structure showed the cyclic "growth-inhibition-growth" phenomenon. This growth mechanism not only refined the grain structure, but also narrowed the columnar region, and improved the mechanical properties of the joint. Compared with the laser oscillating process with constant power, the tensile strength of the joints using the S-curve power was increased by 35.3 %. Moreover, the tensile strength of the welded test coupons with S-curve power was 337 MPa, which is about 99.1% of the base metal (340 MPa). The welded joints using the S-curve power showed larger and deeper dimples, highlighting higher ductility and good plasticity. This paper provides a new approach for the research of laser oscillating welding and the control of laser power to improve the mechanical properties of welded joints. [ABSTRACT FROM AUTHOR]

A directly thixoforged technology of wrought 5A06 alloy with low-cost and short-process was proposed to form a bracket-shape component. The results showed that complex components with a minimum wall thickness of 6 mm, a draft angle of only 1° and an allowance of 1 mm were thixofored successfully. The billet's shape had a slight influence on the filling process of the semisolid slurry during the thixforging. Solid grains in the microstructure of the thixoforged parts exhibited a large deformation degree. It led to an obvious improvement of the mechanical properties of the thixoforged parts. The yield strength (YS) varied from 129.28 MPa to 149.63 MPa, the ultimate tensile strength (UTS) varied from 293.92 MPa to 322.3 MPa, and the elongation varied from 18% to 41.48%. The YS is slightly higher than that of the rolled plate, the elongation is much higher than that of the rolled plate, and the UTS is slightly lower than that of the hot-rolled plate. The increase of plastic deformation degree caused by larger ellipsoid grains is beneficial to improve the mechanical properties of the thixoforged components. The significant improvement of elongation was attributed to homogeneous re-precipitation of the β phase (Mg 5 Al 8) in the thixoforged process. • Directly thixoforging of wrought 5A06 aluminum alloy was studied. • YS and elongation of the thixoforged part reached 149.63 MPa and 41.48%. • The deformation behavior of thixoforging contained a lot of plastic deformation of solid phase. • A possible explanation for extreme high elongation is the homogeneous re-precipitation of the β phase (Mg 5 Al 8). [ABSTRACT FROM AUTHOR]

Molten pool uniformity is a prerequisite for wire and arc additive manufacture to achieve a uniform surface appearance. The thermal boundary is a key indicator to evaluate the thermodynamic state of the molten pool. This paper focuses on thermal analysis through finite element simulation and characterizes the thermal evolution of a molten pool during bottom-up deposition. The peak temperature of the substrate plate increases from 375.7 °C to 623.1 °C when peak current increases from 120 A to 180 A. The temperature gradient decreases from 40 °C/mm to 30 °C/mm. Weld speed increases from 0.15 m/min to 0.25 m/min; the temperature gradient is kept at about 30 °C/mm. Dimensionless thermal conductivity, Ge number, is proposed and defined as the criteria to estimate layer size variation. For Ip = 140 A, the average value of the Ge number is 87.7, and it shows the best numerical stability. Dimensionless thermal conductivity, Ge, is proposed and defined as the criteria to estimate the occurrence of layer size variation. Prolonging heating time and increasing cycle frequency, Ge number shows favorable stability during bottom-up deposition. The experimental results are consistent with analytical conclusions, which proves the validity of the Ge number as an indicator of deposition stability. [ABSTRACT FROM AUTHOR]