6061-T6 Aluminum Alloy Sheets Research Articles

Investigating the formability of 6061-T6 aluminum alloy sheets at elevated temperatures using experimental and numerical methods

The high weight-to-strength ratio of AA6061 aluminum alloys presents increased potential applications in industries such as automotive and aircraft. However, its limited formability at room temperature (RT) restricts its usage. Therefore, in the conducted study, the formability of AA6061-T6 sheets with a thickness of 2 mm was investigated at different temperatures in the range of RT up to 300°C. Both experimental and numerical methods were employed to investigate the forming limit diagram (FLD) of an AA6061-T6 sheet. The tests were conducted using a non-isothermal Nakajima standard die under dry contact conditions. Two damage criteria, the Johnson–Cook and the ductile fracture criterion (DFC), were used in a thermomechanically coupled finite element analysis in Abaqus/Explicit to predict fracture in the AA6061 sheet. To examine the impact of temperature on the friction coefficient in the punch and sheet contact, an atomic force microscope was used to measure the roughness of the sheet, after the FLD tests, were conducted at different temperatures. Results indicate an increase in FLD levels from RT up to 100°C, followed by a decrease, for temperatures surpassing 100°C. Experimental findings underscored the significance of the adhesive wear at elevated temperatures, acting as a decisive factor that hampers the material flow and the sheet deformation, in the contact between the sheet and punch.

A NEW TYPE OF PLUG-IN FRICTION-STIR LAP WELDING BASED ON THE 6061-T6 ALUMINUM ALLOY

In this study a new type of plug-in friction-stir lap welding (PFSLW) is proposed to prepare welded joints based on 4-mm-thick 6061-T6 aluminum alloy sheet. The differences in the cross-sectional morphology, microstructure, cross-sectional hardness and shear properties between the PFSLW joint and the normal friction-stir lap-welding (FSLW) joint are discussed. The results show that the cross-sectional morphology of the PFSLW joint has undergone changes. The PFSLW joint has a mechanical interlocking structure on the advancing side that is beneficial to the connection strength of the joint. The grain structure differs at the boundary between the thermo-mechanically affected zone (TMAZ) and the heat-affected zone (HAZ), and the PFSLW joints show a more pronounced bending deformation of the grain organization near the boundary. The microhardness of PFSLW joints was increased in the TMAZ and HAZ areas, and the lowest hardness is further away from the center of the weld. The failure load of the PFSLW joint has been improved, the microcracks part of the PFSLW joint has a ridge-like structure. In addition, the actual welding width of PFSLW joints was improved.

Experimental study on TIG full welding and single pass welding quality of 6061-T6 aluminum alloy sheet

6061-T6 aluminum alloy plate (3 × 150 × 300 mm3) was welded by tungsten inert gas (TIG) welding. The welding process methods are single-pass welding process and full welding process respectively. The effects of different welding processes on the performance of TIG welding 6061-T6 aluminum alloy were compared and studied. The effects of microstructure and precipitation on the microhardness and tensile strength were analyzed by optical microscope, scanning electron microscopy (SEM), Energy Dispersive Spectroscopy (EDS) characterization, electron backscattering diffraction (EBSD) characterization, microhardness and tensile test. The microstructure of the weld zone is mainly composed of aluminum solid solution (α-Al) dendritic structure and Al–Si eutectic structure. Through EBSD characterization analysis, the average grain size of the weld zone of the full welding process and the single-pass welding process is about 45 μm and 55 μm, and the grain size of the heat-affected zone and the weld zone of the two welded joints does not change significantly. The hardness curves of the two welded joints have the same distribution trend, which is roughly 'W' type distribution. In the tensile test, the tensile strength of the single pass welding process is lower than that of the full welding process, and the fracture of the tensile parts is dimple structure, which is ductile fracture. Through analysis and comparative study, the full welding process is better than the single-pass welding process when welding 6061-T6 aluminum alloy sheet.

Investigation of Mechanical Properties of 6061-T6 Aluminum Alloy Sheets Joined by Cold Metal Transfer (CMT) Using Different Current Intensity

Bu çalışmada, 1,5 mm kalınlığa sahip 6061-T6 serisi alüminyum saclar, alüminyum esaslı (AlMg4,5Mn) teli ile soğuk metal transfer (CMT) yöntemiyle birleştirilmiştir. Numuneler, alın birleştirme formunda hazırlanmış ve birleştirme işlemleri 60, 70, 80 ve 90 A kaynak akım şiddetinde yapılmıştır. CMT işlemlerini gerçekleştirdikten sonra; 6061-T6 serisi alüminyum sacların CMT tekniği ile birleştirilebilirliğini görmek için birleştirmelerin çekme özellikleri tespit edilmiş, mikro sertlik değerleri ölçülmüş ve birleştirmelerin mikro ve makro yapıları incelenmiştir.

Sequentially combined thermo-mechanical and mechanical simulation of double-pulse MIG welding of 6061-T6 aluminum alloy sheets

Double-pulse MIG (DP-MIG) welding is an efficient aluminum alloy jointing technique, which can form heterogeneous aluminum alloy welded sheets with different microstructure and mechanical properties. In order to accurately analyze and predict mechanical properties of welded structures, the geometrical features, local material properties and residual stresses of different welded zones should be synthetically considered in the numerical simulation. This work proposes a sequentially combined thermal-mechanical and mechanical simulation to accurately characterize the mechanical properties of the welded joint through the finite element analysis (FEA) method. The thermo-mechanical simulation was carried out to analyze the transient temperature field and residual stress distribution, which are conductive to build mechanical simulation model with detailed geometric features, the corresponding local material properties as well as attached residual stress. Subsequently, the mechanical simulation was performed to investigate the stress distribution of the welded joint. The deformation behavior and load-carrying capacity of the welded joint from numerical simulation are all in good agreement with corresponding experimental study, which indicates the feasibility and superiority of the developed sequentially combined thermal-mechanical and mechanical simulation method. Also, the stress distribution of the welded joints analyzed by numerical simulation reveals that the fracture evolution mechanism depends on whether the reinforcement has been removed from the welded specimen. The existence of the weld reinforcement leads to the increase of shear stress under tensile condition; hence, the fracture morphology includes equiaxed dimples and elongated dimples. When the reinforcement is removed, the mechanism is trans-granular and inter-granular mixed fracture in the welded zone; otherwise, trans-granular fracture occurs in the heat-affected zone.

Analysis and control of axial pressure in high-speed friction stir welding of alloy sheet

Aiming at the high-speed friction stir welding deformation and thickness reduction of 1 mm 6061-T6 aluminum alloy sheet, the characteristics of the axial pressure of the welding process and its influence on the joint structure and mechanical properties were analyzed in this paper. Experiments were performed to optimize process parameters. A fuzzy controller with axial pressure error and its change rate as input and welding speed as output had been designed to realize axial pressure control during friction stir welding. The welding axial pressure fluctuates slightly around the target value, and the system was stable with the controller. Besides, the microstructure of the corresponding weld nugget area was uniform, dense, and the transition area was uniform without obvious welding defects. The joint hardness distribution was stable with the classic “W” shape distribution. The mechanical properties of the joint were excellent, and the tensile strength reaches 195 MPa, which was about 70% of the base material (290 MPa).

Magnetic Pulse Welding Conditions for High-Tensile Steel of 1 GPa Class and 6061-T6 Aluminum Alloy Sheets

Magnetic Pulse Welding Conditions for High-Tensile Steel of 1 GPa Class and 6061-T6 Aluminum Alloy Sheets

Performance Analysis of Friction Stir Welded Lightweight Aluminum Alloy Sheet

The present research envisaged the performance analysis of a 1-mm thick 6061-T6 aluminum alloy sheet welded by the friction stir welding technique, using optical microscopy, micro-hardness measurement, a tensile test, a friction and wear test, and a salt spray corrosion test. It was found that the grain in the welded zone obtained was refined under each parameter. When the rotating speed of the tool was 15,000 rpm and the traveling speed of the tool was 300 mm·min -1 , the tensile strength of the welded zone was highest, i.e. 74.8% of the base metal. Furthermore, the hardness distribution curve of the welded zone was of the ‘W’ type under each parameter, but the hardness value was lower than that of the base metal. The friction coefficient of the welded zone was lower than that of the base metal under each parameter, and the wear form was found to be mainly adhesive wear accompanied by abrasive wear. The welded zone and the base metal were subjected to salt spray corrosion after 12 hours under each parameter, which had a negative effect on the quality. However, after 12 hours of subsequent corrosion, the quality of each sample and the base material was not obvious.

Experimental Investigation of Friction Stir Welding on 6061-T6 Aluminum Alloy using Taguchi-Based GRA

The use of aluminum alloys, nowadays, is swiftly growing from the prerequisite of producing higher strength to weight ratio. Lightweight components are crucial interest in most manufacturing sectors, especially in transportation, aviation, maritime, automotive, and others. Traditional available joining methods have an adverse effect on joining these lightweight engineering materials, increasing needs for new environmentally friendly joining methods. Hence, friction stir welding (FSW) is introduced. Friction stir welding is a relatively new welding process that can produce high-quality weld joints with a lightweight and low joining cost with no waste. This paper endeavors to deals with optimizing process parameters for quality criteria on tensile and hardness strengths. Samples were taken from a 5 mm 6061-T6 aluminum alloy sheet with butt joint configuration. Controlled process parameters tool profile, rotational speed and transverse speed were utilized. The process parameters are optimized making use of the combination of Grey relation analysis method and L9 orthogonal array. Mechanical properties of the weld joints are examined through tensile, hardness, and liquid penetrant tests at room temperature. From this research, rotational speed and traverse speed become significant parameters at a 99% confidence interval, and the joint efficiency reached 91.3%.

Wear Resistance Analysis of a Lightweight Aluminum Alloy Sheet Friction Stir Joint Area

The friction stir joining experiment was performed on a 6061-T6 aluminum alloy sheet 1 mm thick by optimization of different process parameters, and the microstructure and performance analysis of the joint area using a metallographic microscope, friction and wear testing machine, and scanning electron microscope were evaluated. The results show that the crystalline grains in the joint area of the specimen were refined under a given parameter, and the precipitation of the reinforcing phase improved the performance of the joint area. The best parameters for grain refinement were found to be a rotation speed of 8000 rpm and a traverse speed of 300 mm/min. The specimen obtained at 15,000 rpm and 200 mm/min exhibited the smallest milling weight loss. The smallest average friction coefficient of the specimen was observed at 8000 rpm and 300 mm/min. The friction weight loss trend of the specimens obtained under each parameter was basically the same as the friction coefficient. The wear form of each specimen was found to be mainly the adhesive wear, accompanied by the abrasive one.

Magnetic pulse welding conditions for high-tensile steel of 1 GPa class and 6061-T6 aluminum alloy sheets

Magnetic pulse welding conditions for high-tensile steel of 1 GPa class and 6061-T6 aluminum alloy sheets

Effect of pinless tool shoulder diameter on dieless friction stir extrusion joining of AA 5052-H32 and AA 6061-T6 aluminum alloy sheets

A new spot joining process called dieless friction stir extrusion is proposed, in which simultaneous mechanical interlocking (collar formation) and metallurgical bonding is the key aspect of joint formation. The pinless flat stir tool eliminates pinhole and hook formation, the common defects of friction stir spot welding. Aluminum alloy sheets such as AA 5052-H32 and AA 6061-T6 are spot joined and the effect of change in tool shoulder diameter (10–18 mm) on joint strength and joint formation is evaluated. Lap shear fracture load of 6.22 kN obtained at optimum tool shoulder diameter of 14 mm is higher than that of conventional spot joining techniques. Macrostructure analysis revealed that increase in tool shoulder diameter results in poor mechanical interlocking. Consequently, pin shear failure is common at highest tool shoulder diameter. Critical weak zones of failure are identified. The change in tool shoulder diameter has significant impact on the external joint morphology.

Study on the Ductile Fracture Rule of 6061-T6 Aluminum Alloy Sheet Under Different Strain Conditions

In recent years, some ductile fracture criteria, such as Cockcroft–Latham (C–L) criterion, Brozzo criterion, Oyane criterion, and Gurson–Tveergard–Needleman (GNT) criterion, have been proposed to analyze various material damage behaviors in the plastic deformation process. However, the first three criteria do not consider the effect of shear stress on ductile fracture, and the GNT criterion is a complex structure and a high computational cost due to the consideration of micromechanics. Therefore, Mohr–Coulomb criterion (M–C) has been proposed to describe material damage behaviors with the sample structure and the consideration of shear and principal stress. In this study, the effect of the thickness and the strain rate on the fracture strain is carefully analyzed based on uniaxial tensile tests of sheet metal, and the M–C model of coupled thickness factor is established to predict the ductile fracture of various thickness and strain conditions with 6061-T6 aluminum alloy sheet. Meanwhile, the fracture process of various strain conditions is predicted based on Abaqus/Vusdfld, and the relevant rule of ductile fracture is obtained using the numerical simulation analysis of coupled fracture criterion.

Pinless tool for FSSW of AA 6061-T6 aluminum alloy

Pinless tools have been proposed to eliminate pinhole problems during friction stir welding; while strength of the joint could be decreased. Two probe tools with pin lengths of 2 and 3 mm and two pinless tools with the scroll groove and L-shaped grooves were used for lap welding of 2 mm thick 6061-T6 aluminum alloy sheets. The average tensile shear strength of the weld created by the long probe tool was about 3 times larger than that of the joint fabricated by the short probe tools. This difference was related to the larger stir zone and higher volume of the displaced metal resulted from the higher plunge depth, the higher heat input and more severe stirring induced by the long probe tool. The pinless welds were stronger due to the larger effective cross section area and absence of the keyhole. The application of the proposed pinless tool with L-shaped grooves produced welds with the average tensile shear strength of 2595 N in comparison to 2222 N of the welds created by the pinless tool with the scroll groove. This slight improvement was resulted from the larger stir zone and more severe stirring caused by the grooves with sharp corners.

Microstructure Evolution and Mechanical Properties of High-Speed Friction Stir Welded Aluminum Alloy Thin Plate Joints

Sound friction stir welded (FSW) joints of 6061-T6 aluminum alloy sheets with an 0.8 mm thickness were obtained at conventional speed (2000 rpm, 300 mm/min) and high speed (11,000 rpm, 1500 mm/min). The recrystallization mechanism, precipitate evolution, mechanical properties and fracture behavior were investigated in detail. Microstructure analyses revealed that the grain structure evolution in the nugget zone (NZ) was dominated by continuous dynamic recrystallization. In the process of FSW, high speed facilitates the formation of finer equiaxed recrystallized grains, higher density of dislocations and substructures, and a larger number of precipitates in the NZ compared to the conventional speed, which further significantly improves the hardness and tensile strength of the joints. The maximum tensile strength was obtained with 292.6 MPa, 83.2% for the 6061-T6 aluminum alloy and 122.6% for the conventional-speed FSW joints. This work provides an effective method for preparing FSW aluminum alloy thin plate joints with excellent mechanical properties.

Interface Characterization and Materials Flow Pattern Analysis for Friction Stir Welding Overlap Joints of Mg/Al Dissimilar Alloys

In this paper, the interface characterization and materials flow pattern of overlap joints of dissimilar alloys of 6061-T6 aluminum alloy and AZ31B magnesium alloy welded by friction stir overlap welding with a reverse conical pin tool were investigated. The results shown that: when AZ31B magnesium alloy sheet was placed over 6061-T6 aluminum alloy sheet, and AZ31B magnesium alloy sheet was settled at advancing side while 6061-T6 aluminum alloy sheet was at retreating side, it could eliminate the influence of migration interface on the strength of the lap joints. What is more, the intermetallic compound Mg17Al12 were formed at advancing side of magnesium alloy sheet and retreating side of initial interface between magnesium alloy sheet and aluminum alloy sheet. According to the distribution of intermetallic compound and the characteristics of migration interface, the plastic flowing pattern of metal in welding process was also evaluated.

Microstructure and mechanical properties of twin-wire arc sprayed Ni-Al composite coatings on 6061-T6 aluminum alloy sheet

We have systematically studied the microstructure and mechanical properties of Ni-5wt%Al and Ni-20wt%Al composite coatings fabricated on 6061-T6 aluminum alloy sheet by twin-wire arc spraying under different experimental conditions. The abrasive wear behavior and interface diffusion behavior of the composite coatings were evaluated by dry/wet rubber wheel abrasive wear tests and heat treatment, respectively. Experimental results indicate that the composite coatings exhibit features of adhesive wear. Besides, the Vickers microhardness of NiAl and Ni3Al intermetallic compounds is relatively larger than that of the substrate, which is beneficial for enhancing the wear resistance. With the increase of annealing temperature and time, the interface diffusion area between the Ni-Al coating and the substrate gradually expands with the formation of NiAl3 and Ni2Al3 phases, and is controlled by diffusion of aluminum atoms. The grain growth exponent n of diffusion kinetics of the Ni-Al coating, calculated via a high-temperature diffusion model at 400, 480, and 550°C, is between 0.28 and 0.38. This satisfies the cubic law, which is consistent with the general theoretical relationship of high-temperature diffusion.

Quantifying residual stresses in resistance spot welding of 6061-T6 aluminum alloy sheets via neutron diffraction measurements

Residual strains of resistance spot welded joints of 6061-T6 aluminum alloy sheets were measured in three different directions denoted as in-plane longitudinal (σ11), in-plane transversal (σ22), and normal (σ33). The welding process parameters were established to meet or exceed MIL-W-6858D specifications (i.e., approximately 5.7mm weld nugget and minimum shearing force of 3.8kN per weld confirmed via quasi-static tensile testing). Electron backscatter diffraction (EBSD) and optical microscopy (OM) were performed to determine grain size and orientation. The residual stress measurements were taken at a series of points along the weld centerline at depths corresponding to the weld mid-plane and at both 1mm below the top surface of the plate and 1mm above bottom surface. The residual stresses were captured on the fusion zone (FZ), heat affected zone (HAZ) and base metal (BM) of the resistance spot welded joint. Neutron diffraction results show residual stresses in the weld are approximately 40% lower than yield strength of the parent material. The maximum variation in residual stresses occurs, as expected, in the vertical position of the specimen because of the orientation of electrode clamping forces that produce a non-uniform solidification pattern. Despite the high anisotropy of the welding nugget and surrounding area, a significant result is that σ33 measured stress values are negligible in both the horizontal and vertical directions of the specimen. Consequently, microstructure–property relationships characterized here can indeed inform continuum material models for application in multiscale models.

Effect of Filler Wire Composition on the Nd:YAG Laser Weldability of 6061 Aluminum Alloy

2 mm thick 6061-T6 aluminum alloy sheets were I square butt welded using 3kW Nd:YAG laser. Filler wires of 1 mm diameter, 5183A(Al-4wt.%Mg), 4043A(Al-5wt.%Si) and 4047A (Al-12wt.%Si) were used. The welds made with 4047A wire showed the lowest solidification cracking among the welds investigated. Abundant amount of Al-12wt.%Si eutectic which was observed at the grain boundaries of the 4047A wire feed welds was closely related with the reduced solidification cracking susceptibility. Yield and tensile strength, and formability of the welds made with 4047A wire were improved compared to the welds made with other filler wires, which is attributed to the reduced cracking susceptibility in the welds.

金属間の熱伝達を利用したアルミニウム合金板の部分軟化熱処理

Partial softening heat treatment of aluminum alloy sheets was investigated using heat transfer between the sheet and a couple of heated metal dies to prepare a peripherally softening blank for deep drawing. It was found, from the heat conduction analysis, that the aluminum blank could be heated to the temperature of the heated dies by contacting with them in less than 1 s and the temperature gradient more than 20 degrees/mm could be obtained near the contacting region. The temperature of the sheet contacted with the heated dies depends on heat transfer from the heated dies and the temperature recovery of their surfaces. Production of the peripherally softening blanks was examined for 5052-H24, 1100-H24 and 6061-T6 aluminum alloy sheets. In the blank of 6061 aluminum alloy sheets, the difference in hardness of the central hard part and the peripheral soft part was about 1.8 times. The softening region was changeable according to inner diameters of the heated dies.