6061-T6 Aluminum Alloy Research Articles

Experimental study on mechanical behaviour of friction stir welded aluminium alloy butt joints

The purpose of this paper is to understand the softening extent and stress-strain behavior of the normal-strength 6061-T6, 6013-T6, and high-strength 7075-T6 aluminium alloy butt joints using the novel friction stir welding (FSW) technique. A total of 107 monotonic tensile coupons and 33 Vickers hardness coupons were prepared from 8- or 12-mm thick welded plates using various tool rotation speed, welding transverse speed and tool configurations. The surface morphology, stress-strain curves and hardness distribution laws after welding were evaluated. The W-shaped hardness profiles were clearly observed, with the fracture location positively correlated at the lowest point of Vickers hardness near the edge of the weld toe. The strength reduction and softening extent of extruded aluminium alloys in T6 temper induced by FSW were superior to those of aluminium alloys using fusing welding process outlined in the Chinese and European standards, indicating the effectiveness and applicability of the FSW technique in the formation of components and connections for aluminium alloy structures. Additionally, the current widely used constitutive models generally yielded under-estimations on the strength under large strains. The developed three-stage Ramberg-Osgood model, using seven key input parameters, significantly improved the accuracy and consistent predictions in the full-range stress-strain curve of FSW aluminium alloys. Furthermore, the suggested model could still achieve a great balance between accuracy and practicality when using just three common available parameters with the employment of predictive expressions on other four parameters.

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.

High-Temperature Oxidation of the 304/6061 Welding–Brazing Joint and Its Effects on Corrosion Characteristics

Laser–MIG hybrid welding–brazing was used to weld 304 stainless steel and 6061-T6 aluminum alloy with a thickness of 2 mm. The microstructure, morphology, chemical composition and corrosion behavior of the samples after high-temperature oxidation were investigated. The results reveal that the 304/6061 dissimilar joint had a thicker intermetallic compound layer (7–8 μm) during high-temperature oxidation (HTO) treatment than the sample without HTO treatment (2–3 μm). The oxide film thickness of the 6061 side of the weld joint treated by HTO (2401 nm) increased compared to the samples (181.1 nm) without HTO treatment. Unlike other metals treated by high-temperature oxidation, the high-temperature treatment process in this paper can reduce the corrosion resistance of the base metal and dissimilar joints, and the sequence of the corrosion current density was weld (HTO) >weld>6061 (HTO) >6061>304 (HTO) >304.

New ultra-low cycle fatigue model for metal alloys

Ultra-low cycle fatigue failure is an important ultimate limit state of the structures. Based on the ductile fracture model proposed by the authors, the Coffin-Manson model, and the Miner law, a new model was proposed in this study. The strategy of the proposed model is intended for the prediction of ultra-low cycle fatigue fracture onset covering a wide range of stress triaxiality and being suitable for the variable amplitude straining. Three kinds of metal alloys, Q345qC steel, G20Mn5QT cast steel, and 2024-T351 aluminum alloy, were used to verify the model. The results showed that the proposed model advanced the original Coffin-Manson model greatly. More importantly, the verification demonstrates that the proposed model can predict the ultra-low cycle fatigue fracture initiation over a wide range of stress triaxiality and under variable amplitude straining. Besides, compared with the ULCF-2021 model, the proposed model has a relatively lower average error.

Optimization of 2024-T3 Aluminum Alloy Friction Stir Welding Using Random Forest, XGBoost, and MLP Machine Learning Techniques.

This study optimized friction stir welding (FSW) parameters for 1.6 mm thick 2024T3 aluminum alloy sheets. A 3 × 3 factorial design was employed to explore tool rotation speeds (1100 to 1300 rpm) and welding speeds (140 to 180 mm/min). Static tensile tests revealed the joints' maximum strength at 87% relative to the base material. Hyperparameter optimization was conducted for machine learning (ML) models, including random forest and XGBoost, and multilayer perceptron artificial neural network (MLP-ANN) models, using grid search. Welding parameter optimization and extrapolation were then carried out, with final strength predictions analyzed using response surface methodology (RSM). The ML models achieved over 98% accuracy in parameter regression, demonstrating significant effectiveness in FSW process enhancement. Experimentally validated, optimized parameters resulted in an FSW joint efficiency of 93% relative to the base material. This outcome highlights the critical role of advanced analytical techniques in improving welding quality and efficiency.

Novel methods for optimizing CNC aluminum alloy machining parameters in polymer mold cavities

The examination of the machining of 7075-T6 aluminum alloy polymer mold cavities using Taguchi optimization and analysis of variance is presented in this paper. This study identified the best CNC milling cutting parameters and used a mathematical model to quantify the surface roughness of the machined cavities. The findings showed that while using a flat endmill, the spindle speed multiplied by feed rate contributed 28.01% to surface roughness, and when using a ball endmill, the squared depth of cut contributed 41.27%. Using both flat and ball endmills, the depth of the cut contributed 98.53% to the material removal rate. A refined second-order linear regression model was employed to forecast the endmill-machined surface roughness. The Warp Surf Portable tester measured values that were outside the error range of approximately 0.257% and 2.8%, respectively, for the expected values. Surface roughness has a 99.97% correlation coefficient in the regression model, indicating a very significant link. Additionally, the study improved the cutting parameters for a ball endmill, which were 3005 Rpm, 726.7 mm/min, and 0.43 mm, and for a flat endmill, these were spindle speed (2500 Rpm), feed rate (650 mm/min), and axial cut depth (0.5 mm). The outcomes demonstrated how well the techniques enhanced mold cavity machining and cost estimation using Ra and MRR data. Consequently, these results can be applied to future academic studies and industrial applications.

Initiation and growth of fatigue cracks in sheets with U-shaped notches in the first and mixed modes of fracture

Initiation and growth of fatigue cracks in sheets with U-shaped notches in the first and mixed modes of fracture

Electrochemical behaviour of thermally treated aluminium 2024 alloy exposed to B. mojavensis

The copper-rich zone plays a key role in understanding the deterioration process of 2024 aluminium alloy. The intermetallic on the surfaces makes this alloy susceptible to both local corrosion and microbial colonization. The adhesion of bacteria on the surface could deteriorate the metallic substrate in a phenomenon known as microbiologically influenced corrosion (MIC). The triggering mechanism of MIC in 2024-T3 is unclear. An electro­chemical study was conducted to determine the influence of the second phase (Al2Cu) on the corrosion of the 2024-T3 aluminium alloy exposed to bacteria. The 2024-T3 alloy was thermally treated to increase the amount of Al2Cu by nearly 67 % on the surface. The bacterium under study was collected from the corrosion products of a Chilean Air Force aircraft. The isolated bacterium was identified by 16S RNA sequencing as Bacillus mojavensis (99.99 %). Results obtained by electrochemical impedance spectroscopy showed a decreased impedance of 2024-T3 and an increased impedance of heat-treated, both samples exposed to bacteria. The increased impedance could be associated with the antibacterial effect due to the high ion release of copper on the surface, which can inhibit biofilm formation and biocorrosion.

Laser peening without coating fabricated superhydrophobic aluminum alloy with favorable mechanical properties

This study prepared 2024-T351 aluminum alloy surfaces with excellent hydrophobic properties by laser peening without coating(LPwC) and post-treatment process (silane solution immersion modification treatment). The surface morphology, microhardness, roughness and residual stress of the specimens before and after LPwC were characterized. Besides, the surface composition and droplet contact angle of the specimens before and after LPwC were measured to investigate the mechanism of enhancing the hydrophobic properties by LPwC. The results showed that after LPwC treatment, the surface of the specimen was uniformly distributed with a large number of micro-nano porous structures and the surface roughness was significantly increased. After the modification treatment with fluorosilane solution, the F element on the surface of the specimen significantly increased, the surface energy decreased, the droplet contact angle rose to above 150°, and the sliding angle dropped to below 10°, which imparted the superhydrophobicity on the surface. After LPwC treatment, the grain size of the specimen near-surface layer was reduced, and high magnitude residual compressive stress was generated inside the matrix, which increased the microhardness of material. The as-prepared superhydrophobic surface exhibits excellent water flow repellency and favorable mechanical properties, which promoted the application of superhydrophobic preparation process in the aerospace field.

Effect of laser micromachining crater-array–multi-grooves on the bonding strength and failure mode of aluminum alloy adhesive joints

The strength of aluminium (Al) alloy adhesive joints is essential for aerospace, ship and automotive applications. This study proposes the two-step laser processing of crater-array–multi-groove (CAMG) to maximize the shear strength of adhesive joints for 7075-T6 aluminum alloys. Firstly, the effects of CAMG feature parameters (groove pattern, groove spacing L, and groove depth Gp) on the surface roughness (Sa), shear strength (τ), and microscale failure mode were studied. The failure mode and anchoring structure reveal the influence mechanism of CAMG feature parameters on τ. Then, the parameters are optimized to obtain the best combination that maximizes τ. Finally, the advantages of CAMG were demonstrated by comparing it with a reference specimen and analyzing the surface morphology, wettability, chemical properties, and anchorage structure. The results show that for CAMG the surface had high cleanliness, wettability, and chemical modifications. The multi-scale anchoring structure formed by the grooves, craters, and micropores on the surfaces with the adhesive was sufficiently strong to allow cohesive failure (CF) to occur throughout the bonding region, maximizing τ. When the groove pattern is parallel-groove, L ≤ 100 μm, and the number of scans is N = 2–5, CAMG maximizes τ (∼29.34 MPa). To increase efficiency and save energy, the optimal combination of parameters for laser processing CAMG is parallel-groove, L = 100 μm, and N = 2. Compared with laser processing multi-grooves, CAMG improved the processing efficiency by 3.5 % and reduced the laser energy by 35.2 %. The proposed method shows great advantages in improvement of bonding strength.

Influence of milling parameters on the microstructural evolution mechanism of 7075-T6 aluminum alloy

This study evaluates the influence of milling parameters on the milling process and microstructural changes in 7075-T6 aluminum alloy using experimental and simulation methods. Key findings include a direct correlation between milling parameters and higher chip temperatures, particularly influenced by milling speed which at its third level can cause temperature elevations up to 36 °C, ordered by impact as ap > f > v.Increasing milling depth markedly affects grain recrystallization, especially near the tool's trailing face (P3), leading to a 45.8% reduction in dynamic recrystallization, whereas lower depths expedite this process. Additionally, grain size and number at the leading face (P1) are also depth-dependent, with larger grains diminishing in volume yet increasing in quantity as depth increases. Enhanced milling speeds up to 500 mm/min significantly refine grains to near 1 μm at P1, with an 80.7% rise in recrystallization numbers, while at P3, grain size initially contracts then enlarges at 416 mm/min. Feed rate primarily impacts the quantity of recrystallized grains at the tool tip (P2), with a notable 60.4% increment and a swift transition from larger to smaller grains. Both P1 and P2 experience about a 20% reduction in grain growth due to feed rate, with more pronounced effects at P1 and the fragmentation of larger boundary grains into smaller, irregular shapes.

Effects of sealing and prior shot peening treatments on fatigue behavior of sulphuric acid anodic oxidation coated 6082-T6 aluminium alloy

In this study, the effects of sealing and prior shot peening treatments on the fatigue behavior of the sulphuric acid anodic oxidation coated 6082-T6 aluminium alloy were investigated. Experimental results indicate that the preferential fracture of anodic oxidation coatings due to its higher brittleness and lower fracture toughness as well as the stress concentration of near-interface substrate caused by the interface cyclic dislocation accumulation could cause the fatigue failure of anodic oxidation coated specimens. Consequently, the fatigue property of anodic oxidation coated specimens notably decreases compared to as-machined specimens, with a decrease of 26.7 % in the fatigue limit corresponding to 2 × 107 fatigue cycles. Additionally, the sealing treatment introduces numerous cracks that penetrate the coating entirely, diminishing the coating's resistance to cracking under fatigue loading; this alteration changes the fatigue failure mechanism of anodic oxidation coated specimens, ultimately resulting in a decrease of 15.5 % in the fatigue limit of anodic oxidation coated specimens. Despite exacerbating the surface integrity and increasing the surface roughness of anodic oxidation coated specimens, the prior shot peening treatment increases the fatigue limit of anodic oxidation coated specimens by 82.8 % since the affecting layer beneath the interface plays a crucial role in inhibiting the further propagation of coating cracks into the substrate as well as the crack propagation in the substrate beneath the interface.

Evaluation of Hydrogen Embrittlement of Electroless Ni–P Plated 6061-T6 Aluminum Alloy by Three-Point Bending and Rotating Bending Fatigue Tests

Evaluation of Hydrogen Embrittlement of Electroless Ni–P Plated 6061-T6 Aluminum Alloy by Three-Point Bending and Rotating Bending Fatigue Tests

Study on Fatigue Life of Aluminum Alloy 6061-T6 Based on Random Defect Characteristics.

A certain number of hole-like defects will occur in aluminum alloys under cyclic loading. The internal holes will reduce the strength of the material and cause stress concentration, which will aggravate the development of fatigue damage. A classification method of defect features based on X-ray CT damage data is proposed. The random hole distribution model is established through the linear congruence method and the region division method. The hole parameter is introduced as the intermediate variable of the 3D reconstruction model of internal defects. In the mesoscopic stage, the function relationship between the distribution of random holes and the fatigue life is established based on the coupling relationship between the number and proportion of pores and the fatigue life. In the macroscopic stage, the relationship between the random holes and the macroscopic crack growth life is established by taking the crack length as the damage variable. The crack propagation rate decreased with the increase in the number of holes. The prediction model of the whole life stage is established using the life function from microcrack initiation to macroscopic crack propagation. Finally, the validity of the whole stage fatigue life prediction model is demonstrated through the comparison and verification of experiments, which provides a certain engineering value for the life estimation of 6061-T6 aluminum alloy materials.

Stability properties of 6061-T6 aluminum alloy members with double-layer H-type sections under eccentric compression loads

The stability properties of double-layer H-section aluminum alloy members were studied under eccentric compression loads in this paper. Firstly, six double-layer members were designed and tested under a set of eccentric compression loads with different eccentric distances; as a contrast, six single-layer members were also tested under the same loading conditions; based on the test results, it was compared that the ultimate bearing capacity and buckling modes of the single-layer and double-layer members with different load eccentricity ratios. The experimental results indicated that the stability properties of double-layer H-section aluminum alloy members were better than corresponding single-layer members, but the ultimate strengths of double-layer members were less than the twice of that of single-layer members. A numerical simulating method for single-layer and double-layer H-section aluminum alloy members was established and validated against the experimental results.

Notch Fatigue Property of 7050-T7451 Aluminum Alloy under Bending Resonance Environment

Based on the electromagnetic shaker table, the resonant fatigue testing system and the corresponding conventional fatigue testing system were designed respectively. The fatigue life (S-N) curves of smooth and notched 7050-T7451 aluminum alloy specimens were measured in the range of 105-107 cycles, and the notch fatigue property of 7050-T7451 aluminum alloy under bending resonance environment was studied. The results indicate that the fracture mechanism under bending resonant fatigue environment is roughly the same as that under bending conventional fatigue loading. All the S-N curves obtained through resonant and conventional fatigue tests show a continuously downward trend, and there are no obvious fatigue limits. Notch fatigue property under bending resonance environment presents “stage characteristics”, which increases first and then decreases with the increase of cycles. There is a critical cycle number Nc at 8×105 cycles, corresponding to the maximum fatigue notch factor Kf-max (or the maximum notch sensitivity factor qmax). There are two critical cycles N1 and N2. When N1<N<N2, the notch fatigue property of the material and the corresponding structures under resonance environment requires more consideration than conventional fatigue loading.

An enhanced surface treatment for effective bonding of 7075-T6 aluminium alloys

ABSTRACT This study research focuses on optimising adhesion through surface treatments on 7075-T6 aluminium alloy substrates using a chromium-free protocol. The treatment involves acetone degreasing, NaOH etching, and sulphuric acid-based solution etching. Wettability analysis and scanning electron microscopy were used to characterise the treated surfaces, highlighting the effectiveness of the proposed protocol. The proposed etching protocol was then applied to aluminium alloy substrates, and fracture surfaces corresponding to each treatment were compared. Mechanical testing, specifically double cantilever beam (DCB) experiments, assesses the fracture energy of bonded assemblies in mode I. The results demonstrate that the sulphuric acid-based treatment significantly improves the surface characteristics, leading to enhanced adhesion and optimal fracture energy in bonded aluminium assemblies.

Improved Interface Morphology and Failure Load of Ultrasonic-Assisted Friction Stir Lap Welding Joint of 2024 Aluminum Alloy to 304 Stainless Steel

Achieving high-strength welding joint of aluminum to steel is a highly pressing and challenging task in the manufacturing industries, and friction stir lap welding (FSLW) has advantages for joining these two metals. To further heighten the strength of dissimilar aluminum and steel metals (Al/steel) FSLW joint, the ultrasonic-assisted FSLW (UAFSLW) process was used, and the upper 2024-T4 aluminum alloy and the lower 304 stainless steel were chosen as research object. The results show that the addition of ultrasound eliminates the micro pores, changes the aluminum-rich intermetallic compounds (IMCs) into the iron-rich IMCs and enhances the micro and macro mechanical interlocking structures along the Al/steel lap interface. Under the rational IMCs layer thickness lower than 1.5 μm, the UAFSLW joint has the failure load higher than the traditional FSLW joint. The maximum failure load of UAFSLW joint reaches 7.06 kN, and the loading capacity of this joint is higher than that of reported Al/steel traditional FSLW joint. The UAFSLW process is an effective way to fabricate the high-strength Al/steel lap joint.

Tungsten Inert Gas Welding of 6061-T6 Aluminum Alloy Frame: Finite Element Simulation and Experiment.

In order to address the irregularity of the welding path in aluminum alloy frame joints, this study conducted a numerical simulation of free-path welding. It focuses on the application of the TIG (tungsten inert gas) welding process in aluminum alloy welding, specifically at the intersecting line nodes of welded bicycle frames. The welding simulation was performed on a 6061-T6 aluminum alloy frame. Using a custom heat source subroutine written in Fortran language and integrated into the ABAQUS environment, a detailed numerical simulation study was conducted. The distribution of key fields during the welding process, such as temperature, equivalent stress, and post-weld deformation, were carefully analyzed. Building upon this analysis, the thin-walled TIG welding process was optimized using the response surface method, resulting in the identification of the best welding parameters: a welding current of 240 A, a welding voltage of 20 V, and a welding speed of 11 mm/s. These optimal parameters were successfully implemented in actual welding production, yielding excellent welding results in terms of forming quality. Through experimentation, it was confirmed that the welded parts were completely formed under the optimized process parameters and met the required product standards. Consequently, this research provides valuable theoretical and technical guidance for aluminum alloy bicycle frame welding.

Residual stress effects on short crack propagation behavior in friction stir welded 7075-T6 aluminum alloy panel under biaxial loading: An experimental and numerical study

The effects of residual stress on short crack propagation behavior of friction stir welded (FSWed) 7075-T6 aluminum alloy panel was investigated under biaxial loading. The biaxial fatigue tests were carried out on three kinds of cruciform samples, including base material (BM) cruciform sample and FSWed cruciform sample with crack perpendicular or parallel to the weld. Scanning electron microscope (SEM) fractography was conducted to identify and relate fracture surface features to governing fatigue damage mechanisms. Finite element method combined with stress intensity factor (SIF) analysis was used to simulate the biaxial fatigue propagation. In a comparison of the crack path in BM and FSWed cruciform samples, experimental and numerical results showed that residual stress can change the nominal biaxiality ratio, leading to crack path changes in FSWed cruciform sample with crack parallel to the weld, and the curved fatigue crack front formed on the fracture surface due to the non-uniform distribution of the residual stress through the thickness. The fatigue damage mechanisms are different depending upon the biaxiality ratio as well as the weld direction.