Alloy AA2024-T3 Research Articles

Heat generation, plastic deformation and residual stresses in friction stir welding of aluminium alloy

The interactions among thermal history, plastic deformation and residual stresses in the friction stir welding (FSW) process under different welding parameters have been widely considered a crucial issue and still not fully understood. In the present study, a novel three-dimensional fully coupled thermo-mechanical finite element (FE) model based on Coupled Eulerian-Lagrangian approach (CEL) has been developed to simulate the FSW process of aluminium alloy AA 6082-T6 and to analyse the thermo-mechanical interaction mechanisms under different welding conditions. The numerical model successfully simulates the plunge, dwell, and welding steps in FSW and captures the evolution of temperature, plastic deformation, and residual stresses in the welded joint. The obtained results were validated by experimental testing with observed cross-weld thermal history, optical macrography and residual stress measurement using the neutron diffraction technique. The results reveal that the tool rotation speed governs the temperature evolution; the peak temperature increased from 740 to 850 °K when the tool rotation speed rose from 800 to 1100 rpm. The rotational speed also affected the plastic deformation, material flow, and the volume of material being stirred during the welding process. Higher plastic deformation is formed in the stirring zone by increasing the tool angular velocity. This behaviour led to an increase in the stirring effect of the welding tool, reduction of the tunnel defect size and enhancing the quality of weldments. The distribution of residual stresses in different zones of the FSW joints has been found to have an M-shaped profile. A significant tensile residual stress is characterised in the edge of the nugget zone in both longitudinal and transverse directions, balanced by compressive stresses in the thermo-mechanically affected zone, heat-affected zone and base metal. The presented FE modelling provides a reliable insight into the effects of the welding parameters on the weld quality of FSW joints and process optimisation with minimised experimental trials.

Casting and forming of nano hard aluminum oxide film on the modified 6061 Al alloys for NARSSCube satellite structure

This research focuses on metal additive manufacturing (MAM) and examines the impact of alloying materials on the anodized produced layer, placing particular emphasis on its use in the construction of the NARSSCube satellite's frame. To enhance the AA6061-T6 Al alloy's mechanical and physical qualities, Mg, Mn, Si, and Cr concentrations were changed. As a result, seven different alloys were cast, and their mechanical and physical characteristics were assessed. It is essential to anodize aluminum alloy AA6061-T6 in H2SO4 solution in order to produce an aluminum oxide film (AOF) that increases corrosion and wear resistance. This study looked into how the chemical composition of the AA6061-T6 aluminum alloy, particularly Mn, affected the production of the nano hard aluminum oxide film (NHAOF) at fixed anodization conditions of 4 °C and 20 V. Calculations were made on the thickness variation at various operating voltages throughout the anodizing process. The differences in NHAOF thickness were investigated using optical and scanning electron microscopes. Finally, anodizing the alloy with low Mn Wt.% (0.005 wt% S6) at 4 °C, 20 V, and a duration period of 120 min in a 10 % H2SO4 solution produced the oxide coating with the highest thickness (53 μm) and high-performance attributes. An increase in the hardness ratio, resistance to plastic indentation, and elastic recovery are all results of the surface's harder (5.86 Gpa) than the un-anodized sample's (1.18 Gpa) surface.

Refill friction stir spot welding of AlSi10Mg alloy produced by laser powder bed fusion to wrought AA7075-T6 alloy

In this study, refill friction stir spot welding (RFSSW) was used to join AlSi10Mg, produced by laser powder bed fusion (LPBF), to high-strength wrought AA7075-T6 alloy. The investigation showed the best mechanical properties and integrity of the joint are achieved with medium heat input, where the optimal balance between hook height and integrity was observed. The welded additive manufactured alloy shows accentuated softening in the hook region of the thermo-mechanically affected zone. The feasibility of RFSSW for joining LPBF AlSi10Mg to high-strength wrought alloys was confirmed, showing high potential for further investigations and industrial applications.

Effect of additional heating on corrosion of dissimilar friction stir welded aluminum alloys

In the present work, aluminum alloys AA2014-T6, AA6061-T6 and AA7075-T651 are used to fabricate two different dissimilar friction stir welds of AA6061-AA7075, and AA6061-AA2014 using a threaded tool pin with three flat faces at tool rotational speed of 1200 rpm, weld speed 98 mm/min and employing additional secondary heating. Additional heating is provided using butane gas torch which principally expedites better material mixing supplementarily resulted in increased corrosion resistance. The higher working temperature provides steeper cooling rates necessary for grain refinement and additional breakdown or dissolution of corrosion susceptible particulates. The joints fabricated sustained corrosive environments for adequate duration and ultimate tensile strength of the joints are retained after 14 days of immersion in corrosive saline solution. AA6061 experienced pitting as well as intergranular corrosion, AA2014 shows pitting and AA7075 exhibited exfoliation corrosion. The fracture morphology shows substantial size dimples indicating the loss in ductility for all the joints due to the after effects of heating.

Damping behaviour of submerged friction stir welded AA6061-T6 alloy with addition of brass interlayer

• The present paper mainly investigates the damping behaviour of AA6061. • Grain refinement was studied with the help of electron back scattered diffraction. • Intermetallic behaviour was studied under the scanning electron microscope. • Damping behaviour is correlated with grain size and intermetallic behaviour. The effect of brass interlayer and water cooling on the damping behavior of friction stir welded AA6061 was investigated in the present work. The results revealed that weld samples showed better damping capacity than base metal attributed to the grain refinement. Moreover, the damping capacity of weld with the addition of interlayer is enhanced due to more grain refinement, formation of hard intermetallics, and high inherent damping capacity of brass. The reduced intermetallics and formation of smooth interface obtained for water-cooled weld attributed to the faster cooling rate improved the mobility of grain boundaries which enhanced the damping capacity than natural cooling. The water-cooled weld with interlayer showed better damping at high temperatures than other weld joints due to the increased grain boundary area.

The effects of laser peening treatment on the very high cycle fatigue properties for AA2024-T351 alloy using a crystal plasticity framework

The effects of laser shot peening (LSP) on very high cycle fatigue (VHCF) properties of AA2024-T351 alloy were investigated using the combination of experiment and modified crystal plasticity finite element (CPFE) method. The experimental observation found a contradictable result that the fatigue life decreased after laser peening with relatively high pulse energy in this work. The fatigue fracture observation shows that there are obvious facets and refined grains on the shot peening surface, which are not uniform and their aspect ratio is obviously larger than that of the matrix material. In particular, the fracture surface of the sample treated with 20 J pulse energy shows a highly distorted zig-zag crack propagation path. In order to further understand the ultra-high cycle fatigue failure mechanism of aluminum alloy treated with laser shot peening, a modified crystal plasticity (CP) model was applied to find a possible explanation for the contradictable experimental results. In this model, the critical resolved shear stress (CRSS) evolution of the deformation systems in the CP model was variable due to the refined average grain size after different laser peening conditions using the Hall-Petch type relationship. Additionally, the effects of grain morphology characterized by aspect ratio were considered after LSP of AA2024-T351. The fatigue indicator parameters (FIPs) were calculated based on the modified CPFE model under cyclic low stress amplitudes to estimate the fatigue driving force for fatigue crack initiation and microstructural small crack propagation. It is found that the LSP treatment has a beneficial effect on the fatigue properties only considering the refined influence of grain size. However, LSP has a detrimental effect on VHCF properties when considering the combined influences of grain refinement and the changing of grain aspect ratio due to the laser peening surface treatment with relative high pulse energy in this work.

A Novel Friction Stir Deposition Technique to Refill Keyhole of Friction Stir Spot Welded AA6082-T6 Dissimilar Joints of Different Sheet Thicknesses.

Joining dissimilar sheet thicknesses of AA6082-T6 alloys by friction stir spot welding (FSSW) provides many advantages in automotive and aerospace applications. The formed keyhole at the end of the FSSW process is one of the typical features after the welding process, which owns the same size as the rotating pin that remains at the joint center. This keyhole destroys the joint continuity and can stimulate serious stress concentration when the FSSW joint bears an external force. To solve this issue, a novel refilling technique was developed for the FSSW keyholes using a friction stir deposition (FSD) technique. The FSSW joints of AA6082-T6 sheets were welded at various rotation speeds from 400 to 1000 rpm and a constant dwell time of 3 s, where a 2 mm sheet thickness was an upper sheet, and a 1 mm sheet thickness was a lower sheet. All the keyhole refilling processes were achieved using a specially designed AA2011-T6 consumable rod to be used for friction stir deposition of continuous layers at a constant deposition parameter of 400 rpm consumable rod rotation speed and a 1 mm/min feed rate. The heat input energy for both the FSSW and refilled FSSW lap joints was calculated. In addition, the FSSW and the FSD temperatures were measured. Macrostructure, microstructure, and mechanical properties in terms of hardness and tensile shear maximum load were evaluated for both the friction stir spot welded (FSSWed) and the refilled FSSW lap joints. The obtained results showed that the keyhole could be successfully refilled with defect-free continuous multilayers after the refill friction stir spot welding (RFSSW) process. All the RFSSW lap joints showed higher tensile shear loads than that given by the FSSW (before refill) lap joints. The RFSSW joint (welded at 600 rpm/3 s and refilled at 400 rpm/1 mm/min) showed a higher tensile shear load of 5400 N ± 100 compared with that recorded by the unrefilled joint (4300 N ± 80). The fracture location and fracture surface of the FSSW and RFSSW were examined and discussed.

Microstructural and Mechanical Behavior of Friction-Stir-Welded AA6061-T6 and AZ31 Alloys with Improved Electrochemical Corrosion

Microstructural and Mechanical Behavior of Friction-Stir-Welded AA6061-T6 and AZ31 Alloys with Improved Electrochemical Corrosion

Evaluating the corrosion behaviour of AA6061-T6 alloy and its friction stir welded joints

ABSTRACT The cold rolled aluminium alloy (AA6061-T6) and its friction-stir welded joints (with varied tool-tilt angle and joint configuration) were investigated for their corrosion performance using a corrosion immersion test in two stages. First, the influence of corrosion conditions on the performance of base metal was investigated using the design-of-experiments approach with the central composite design of response surface methodology. Among the three input corrosion variables (namely time, temperature and NaCl-concentration) selected at three levels each, the contribution of temperature to corrode the base metal was found to the order of ≈50%, followed by time (21%) and NaCl-concentration (7%). Further, parameters were optimised to attain minimum and maximum corrosion rate conditions. In the second-stage, the optimised corrosion conditions were used to study the corrosion behaviour of the welded joints. Among all welds, the single-pass joint fabricated with 0° tilt angle showed minimum corrosion rate but possessed 96% higher mass-loss compared to the base metal. Moreover, the corrosion rate was found to increase with the increase in tool-tilt angle, as-well-as with the change in joint configuration from single-pass to double-pass. The optical and scanning electron microscopy revealed the pitting and intergranular corrosion to be the dominating corrosion mechanisms for the base metal and welded joints.

Strengthening mechanism of high-pressure linear friction welded AA7075-T6 joint

The high-pressure linear friction welding of AA7075-T6 alloy was performed to investigate the relationship between the microstructures and mechanical properties of the joints. It was found that the joint obtained by the high-pressure linear friction welding of 470 MPa exhibited a complete flat hardness distribution across the welding line by maintaining precipitation strengthening. The precipitates formed in the weld regions of the AA7075-T6 joints are mainly composed of MgZn2 phase and Cr-bearing dispersoids. At the low pressure of 60 MPa, the volume fraction of both MgZn2 phase and Cr-bearing dispersoids at the weld center significantly decreased due to the relatively high welding temperature. Consequently, the softening occurred at the weld interface of the joint fabricated at low pressure even though the equiaxed grains were refined due to the DRX, thus the joint efficiency was approximately 58%. On the other hand, at high pressure (i.e. low welding temperature), the volume fraction of the Cr-bearing dispersoids was maintained even though the volume fraction of the MgZn2 phase was reduced, due to the high thermal stability of the Cr-bearing dispersoids. Therefore, a sound joint with superior mechanical properties, which is equivalent to the base material, was obtained since the effect of the precipitation strengthening in the weld regions was maintained in the high-pressure linear friction welded AA7075-T6 joint.

Microstructural and Mechanical Properties of AZ31B to AA6061 Dissimilar Joints Fabricated by Refill Friction Stir Spot Welding

Dissimilar friction stir spot welds (FSSW) between the magnesium and aluminum alloys are joined, using a novel approach called refill friction stir spot welding. The present work aims to evaluate the macrostructural and mechanical properties of refill friction stir spot welded AZ31B and AA 6061-T6 alloys in two combinations, i.e., identical Mg-to-Mg and dissimilar Mg-to-Al joints, and the results are compared with the results obtained in conventional friction stir spot welding. The hardness profiles of the similar welds had the appearance of a W-shape, and the Thermo mechanically affected zone and heat-affected zone of both methods had lower hardness values than the rest of the weld. Along with the interface between the aluminum and magnesium sheets, a thin intermetallic compound layer of Al12Mg17 has been identified, which has led to an increase in hardness. The static shear strength of both similar and dissimilar refill spot friction welds was much greater than that of traditional spot friction welds. In both similar and dissimilar spot friction welds, two distinct failure scenarios are discovered.

Comparative study of microstructure and mechanical properties using a novel filler rod ER 4943 and autogenously butt welded joint during laser welding of AA 6061-T6 in 1G position

A 4 mm thick heat-treated aluminum alloy AA 6061-T6 has been butt welded in 1 G position using a 12-kW disk laser. A novel high magnesium content filler rod ER 4943 belonging to the 4xxx series of aluminum alloys has been used to investigate its effects on microstructure, mechanical properties and alloying elements segregation in the fusion zone. The results have also been compared with an autogenous laser butt welded joint case. A solidified microstructure has been analyzed by EBSD. It was found that additional solute content brought by filler rod into the molten pool caused a higher proportion of equiaxed grain zone after solidification due to an enhanced constitutional supercooling ahead of solid/liquid interface. For an autogenous butt welded joint, the columnar morphology sustained for a longer period and a narrower equiaxed grain zone were observed. Point analysis by an EDS revealed a higher retention of magnesium and silicon inside the solid solution with filler rod welding. In addition, the area map of magnesium also observed a denser distribution of magnesium inside the fusion zone. Both hardness and tensile strength of filler rod welded joint were higher than without filler rod welding. It is believed that a higher proportion of equiaxed grains and additional solute content within the solid solution are the primary causes of higher mechanical properties owing to hampered dislocation motion. The much desirable results obtained in terms of microstructure and mechanical properties could be of great significance to the welding industry.

Effect of Welding Parameters on Mechanical Properties and Microstructure of Friction Stir Welded AA7075-T651 Aluminum Alloy Butt Joints.

The aim of this study was to examine the mechanical properties of 5-mm-thick AA7075-T651 alloy using three different welding velocities, 50, 75 and 100 mm/min, and four various sets of tool rotation speeds: 400, 600, 800 and 1000 rpm. All obtained joints were defect-free. In all cases, the values of UTS exceeded 400 MPa, corresponding to 68.5% minimum joint efficiency. The highest value of 447.7 MPa (76.7% joint efficiency) was reported for the joint produced via 400 rpm tool rotation speed and 100 mm/min welding velocity. The SZ microstructure of the strongest joint was characterized by a 5.2 ± 1.7 μm grain size and microhardness of approximately 145 HV0.1. The TMAZ/HAZ interface was identified as the low-hardness zone (105–115 HV0.1, depending on parameters), where the failure of the tensile samples takes place. The fracture mechanism is dominated by a transgranular ductile rupture with microvoid coalescence.

Fatigue behaviour of re-entrant auxetic structures made of the aluminium alloy AA7075-T651

An investigation of the fatigue behaviour of the re-entrant auxetic structures made of the aluminium alloy AA 7075-T651 is presented in this study. The analysed auxetic structures represent a new class of cellular structures that show anomalous deformation responses such as negative Poisson’s ratio. In the proposed work, the influence of the unit cell orientation on the crack path and fatigue life was studied using experimental and computational approaches. The Low Cycle Fatigue (LCF) tests were performed at load control with the load ratio 0.1 in tension. In the LCF tests five loading levels were selected, and at least two tests were performed at each loading level. The same loading conditions were then applied in the computational model in the framework of the ANSYS software package, where a nonlinear kinematic material model was applied to obtain the stress–strain relationship. The strain-life approach, with consideration of the Morrow mean stress correction, was then used to obtain the fatigue life of the analysed auxetic structures. The experimental and computational results showed that the unit cell’s orientation has a minor influence on the fatigue life of both analysed auxetic structures, but impact on the direction of the fatigue failure path significantly.

Tailoring surface properties of aerospace-grade aluminium alloy through solid-state friction stir processing

Aerospace grade AA7075-T6 alloy was friction stir processed at different tool rotation speeds and traverse speeds with a square profiled pin and the resulting microstructural evolution, texture formation and mechanical properties were analysed in this study. Low-magnification optical macroscopy, electron back-scattered diffraction, and bulk-texture analysis were conducted to probe material consolidation, microstructural grain refinement and crystallographic orientation of the grains inside the stir zone. Mechanical properties such as microhardness and tensile strength analysis were further conducted and the results correlated. Macrostructural observations show better consolidation in the specimens processed at 1050 r/min with 30 and 60 mm/min traverse speeds, and 1200 r/min with 30 mm/min as traverse speed. Electron back-scattered diffraction results confirm significant grain refinement in the sample processed at 1050 r/min, 60 mm/min and having a minimum grain size of 3.49 μm. Bulk-texture analysis indicated the presence of randomized grain orientation with copper and S as major texture components. Maximum hardness and tensile strength of 147.1 HV and 432 MPa were exhibited by the specimen processed at 1050 r/min and 60 mm/min due to grain refinement, increased dislocation density and finely distributed strengthening precipitates. Unprocessed base material displayed bimodal ductile and brittle mode of failure, while ductile fracture behaviour was exhibited by the friction stir processed specimen.

Electrodeposition of silane/reduced graphene oxide nanocomposite on AA2024-T3 alloy with enhanced corrosion protection, chemical and mechanical stability

Hydrophobic silane/reduced graphene oxide (rGO) nanocomposites were successfully constructed on an AA2024-T3 aluminum alloy surface using a facile co-electrodeposition process. The composition and morphology were characterized by ATR-FTIR, XRD, Raman spectroscopy, EDX, XPS and SEM. The results revealed that the implanted GO nanosheets were partially reduced and successfully covalently bonded with silanol groups to fabricate a more compact and denser coating. Electrochemical measurements demonstrated that the electrodeposited silane/rGO nanocomposite markedly decreased the corrosion rate of the AA2024-T3 alloy in 3.5 wt% NaCl solution. The protection efficiency was maintained over 96% after 120 h of exposure, presenting excellent chemical stability. Meanwhile, a sand paper abrasion test was performed to evaluate the mechanical robustness and the contact angle was reduced by only 4.5° after 150 abrasion cycles. The excellent anti-corrosion property and mechanical robustness, along with the feasible electrodeposition procedure, show its great potential for industrial applications.

A novel post-weld composite treatment process for improving the mechanical properties of AA 6061-T6 aluminum alloy welded joints

The welded joint for a heat-treated aluminum alloy AA 6061-T6 showed softening in the fusion zone (FZ) and the heat-affected zone (HAZ). This paper proposed a post-weld composite treatment process that overcame the joint softening by coupling the solubilization treatment (ST), aging treatment (AT), and cold rolling (CR). Three post-weld composite treatment processes were investigated to reveal the effect of the interaction between precipitation hardening and work hardening on joint mechanical properties. Experimental results showed that the post-weld “ST-AT-CR” composite treatment process could improve the microhardness of the FZ and HAZ to the level of the original base metal (BM), and the joint strength and ductility could reach up to 100 % and 67 % of the BM, respectively. On the other hand, it was also observed that the post-weld “CR-ST-AT” composite treatment process could make the joint softening more serious. The higher pre-existing dislocation density by the CR process would provide more diffusion channels for the solute atoms during the ST-AT process and promote the over-aging of strengthening phases, while the ST-AT process would significantly reduce the pre-existing dislocation density.

Development of friction stir powder deposition process for repairing of aerospace-grade aluminum alloys

This paper presents development of a novel friction stir powder deposition (FSPD) process for potential repairing applications of aerospace-grade aluminum alloy AA6061-T6. Powder form of the deposition material was thermo-mechanically processed at a temperature below its melting point. Influence of various process parameters on thermal cycles, deposition quality, deposition height, microstructure, and mechanical properties have been studied. Higher degree of deformation resulted in a dynamically recrystallized fine-grained microstructure which gave better mechanical properties. EDS study revealed uniform distribution of the major alloying elements throughout the deposition. Best quality deposition showed maximum microhardness and wear rate 0.84 and 1.07 times respectively than the substrate AA6061-T6 alloy. FSPD process is found to be capable of depositing maximum height of 0.45 mm, maximum deposition efficiency of 22% with an energy consumption of 73.7 J/mm 3 per unit deposition material consumption. Moreover, it used current in the range of 5-7 Ampere. This research shows that FSPD process can provide considerable cost and energy savings over fusion-based additive manufacturing processes making it a viable alternative for repairing aerospace-grade aluminum alloys. • Developed friction-stir powder deposition as a solid-state AM process for aerospace-grade Al alloys. • Max. deposition height: 0.45 mm; deposition efficiency: 22%; Avg. peak temperature: 293 °C. • Higher deformation gave dynamically recrystallized fine-grained microstructure. • Uniform distribution of alloying elements in the deposition. • Deposition microhardness and wear rate are 0.84 and 1.07 times than substrate AA6061-T6.

Electrochemical corrosion of AA6061-AA7075 double sided FSW joints prepared with and without secondary heating

The present study aims to evaluate corrosion behavior of different zones in the double-sided dissimilar friction stir weld between precipitation hardening aluminum alloys AA6061-T6 and AA7075-T651 of 12.7 mm thickness obtained without and with employing secondary/additional heating. Each specific zone of the welds is tested for corrosion potential, corrosion current and impedance spectroscopy. The stir zone formed is more corrosion resistive than AA7075 but less in comparison to AA6061. The corrosion resistivity of AA7075 dominated region increases significantly on the application of secondary heating. The increase is attributed to the disintegration of large corrosion susceptible precipitates due to intense mixing and stirring facilitated at elevated temperature with the application of additional heating. Although, AA6061 experienced trivial decrease in corrosion resistance as high working temperature resulted in increased grain boundary along with high misorientation angle. The scanning electron microscopic images and elemental line scan at corroded stir zone identified AA7075 as the sacrificed alloy due to galvanic coupling with AA6061 at macroscopic scale and dissolution of Mg/Si at microscopic scale. The regions with higher percentage of high angle grain boundaries observed to undergo faster corrosion rates. The heat produced in second pass left annealing effect on prior welded region wherein lower microhardness is noted. • Corrosion resistance of SZ in AA6061-AA7075 DS-FSW joints is enhanced compared to AA7075 while reduced compared to AA6061. • HAZ and TMAZ on RS (AA7075) showed significantly increased corrosion resistance employing secondary heating. • Breakdown of corrosion sensitive intermetallic helped in increasing corrosion resistance. • Slight drop in corrosion resistance of AA6061 observed after secondary heating as increased fraction of HAGBs promoted IGC.

Friction Stir Welding of Thin Sheets of the AA2024-T3 Alloy with a Ceramic Tool: RSM and ANOVA Study

In this study a new ceramics tools with different groove distributions were designed and manufactured in order to enrich technological storage of joining thin-wall structures and obtain sound joint with high quality of alclad AA2024-T3 alloy of 0.5 mm in thickness. Four types of tools were tested, without grooves, with 1, 2 and 6 grooves. The tools are made of two materials. The straight shank is made from tungsten carbide and tool body made from ceramics strengthened with whiskers. The influence of technological parameters on the strength of FSW joints was tested by the RSM (Response Surface Methodology) and ANOVA (analysis of variance) method. The least durable weld is produced by a tool without grooves. The 1 and 2-flute tool produces a good quality weld over a wide range of tool speeds. It has been shown that the grooves on the tool shoulder significantly affect the quality of the obtained FSW joint.