6061-T6 Alloy Research Articles

The effect of precipitates on low-cycle fatigue behavior of WE54 magnesium alloys under stress-controlled mode

The precipitates have a significant influence on fatigue behavior in magnesium (Mg) alloy. In this work, the effects of precipitates on deformation mode, cracking mode and mechanical behavior during low-cycle fatigue under stress-controlled mode in WE54 Mg alloy at room temperature (RT) was analyzed quantitively and statistically via quasi-in-situ electron backscattered diffraction (EBSD), slip trace analysis, coupled with transmission electron microscopy (TEM). The results reveal that precipitates promoted the activation of pyramidal < c + a > dislocation slip and suppressed the activation of tension twinning in the T6 alloy. In the T4 alloy, persistent slip band (PSB) induced cracking together with intergranular cracking dominated fatigue damage, while intergranular cracking was the primary cracking mode in the T6 alloy. The obvious cyclic hardening behavior of the T4 alloy was attributed to dynamic precipitation, whereas suppressed dynamic precipitation, restrained multiplication of dislocations, together with the appearance of PFZ generated the marginal cyclic hardening behavior in the T6 alloy. Both the T4 and T6 alloys exhibited ratcheting behavior, and precipitates suppressed ratcheting deformation in the T6 alloy. Moreover, the underlying mechanism for the higher fatigue resistance in the T6 alloy was also discussed.

Investigation of the effect of minimum quantity lubrication and Ranque–Hilsch vortex tube cooling on cutting forces, surface roughness and cutting zone temperature in turning Al 6082 T4 alloy

Aluminium alloys are widely utilized, particularly in the automotive and aerospace industries, because of their great corrosion resistance, high strength/density ratio and propensity to increase mechanical qualities during ageing. With this widespread use, there are also various machining problems. Therefore, in this study, the cutting forces, average surface roughness and cutting zone temperature of different cooling conditions in turning Al 6082 T4 alloy were investigated. In the experiments, three different cutting conditions (Ranque–Hilsch vortex tube (RHVT), minimum quantity lubrication (MQL), and dry) were used in the experiments. As cutting parameters, three cutting speeds and feed rates (500, 625 and 800 m/min and 0.1, 0.125 and 0.15 mm/rev) were chosen. Taguchi-based grey relation analysis was applied to the data obtained after the experiments. As a result, it has been observed that MQL and RHVT methods positively affect the cutting forces, average surface roughness and cutting zone temperature values. As a result of Taguchi-grey relational analysis, optimum results were obtained with RHVT cooling, 800 cutting speed and 0.1 feed rate.

Effect of continuous retrogression and re-ageing treatment on mechanical properties, corrosion behavior and microstructure of an Al-Zn-Mg-Cu alloy

The mechanical properties, electrical conductivity, corrosion behavior and precipitation evolution of an Al-Zn-Mg-Cu alloy during the continuous retrogression and re-ageing (CRRA) treatment with slow heating-cooling rates are investigated systematically. The results reveal that the partial dissolution of pre-existing precipitates (GP Ⅰ zone and η' phase), and the growth of remaining precipitates, as well as the formation of new η' phase occur in the retrogression heating process, which are similar to the phase transformation in the retrogression stage of the discontinuous retrogression and re-ageing (DRRA) treatment. The isothermal retrogression stage of the CRRA treatment plays a key role for precipitates coarsening. The alloy retrogressed at 190 °C for 10 min and re-aged (RRA190–10 alloy) obtains high strength and excellent corrosion resistance, as well as high electrical conductivity simultaneously. Furthermore, the thermodynamic stability of the precipitates in RRA190–10 alloy (η' phase + η phase) is greater than that of T6 alloy (GP Ⅰ zone + η' phase). The microstructure features related to the property changes are discussed.

On the laser surface pre-treatment to enhance the surface texture, wettability and adhesion bonding strength of aluminium 7075-T6 laminates

ABSTRACT In this study, a laser surface pre-treatment strategy was applied to aluminium 7075-T6 alloy, in which the laser power, speed and frequency were varied to determine the best modified surface property in terms of surface wettability. Surface texture, topography, roughness, contact angle and adhesive bonding strength of the treated surface were measured and characterised. Results showed that the laser-treated surface at a laser power of 30 W, speed of 1.2 m/s and frequency of 8 kHz provided the highest surface wettability by showing the lowest contact angle of 17°, which was attributed to the deeper surface cavities and higher surface roughness. The laser treatment increased the adhesion strength up to 8.5 MPa which was 45% higher than that of the untreated surface (of 5.9 MPa). Its adhesion strength nearly matched with that of the oxalic acid treatment. The laser-treated failed specimen shows predominantly adhesion–cohesion failure mode with a strong interfacial bonding. FTIR spectra confirmed the presence of required functional chemical groups of the adhesive after curing, demonstrating a strong bonding force and affinity between the adhesive and the modified surface. The findings clearly indicate that the laser surface pre-treatment would be a viable surface modification strategy without environmental and health hazard to provide adequate strength in the adhesively bonded joints.

Effect of post-heat treatment on the microstructure, mechanical, and corrosion properties of laser powder bed fused Al–Zn–Mg–Cu–Si–Zr–Er alloys

Three different post-heat treatments, including direct aging (DA), solution heat treatment + precipitate hardening (T6), and retrogression and re-ageing (RRA), were carried out on a Si–Zr–Er modified Al–Zn–Mg–Cu alloy, which is manufactured by laser powder bed fusion (LPBF). The results show that direct aging maintains the cellular structure of the as-printed (AP) alloy, while T6 and RRA promoted the damage and decomposition of the cellular structure. The size of the primary Al3(Er,Zr) phase increased after heat treatment, and secondary Al3(Er,Zr) phases were uniformly distributed in the matrix with a size of 5–20 nm. The Mg2Si phase in the DA alloy was a long strip pattern, but uniformly distributed in the T6 and RRA alloy. The ultimate tensile strength of the AP, DA, T6, and RRA alloys reached 468, 474, 389, and 354 MPa, respectively. The size, shape, and distribution of the Al3(Er,Zr) and Mg2Si phases have a significant impact on their corrosion resistance, with the latter having a stronger effect. To sum up, the strength of the DA alloy is increased, but its corrosion performance is decreased with heat treatment. On the other hand, the strength of the T6 and RRA alloys is somewhat sacrificed, but their plasticity and corrosion resistance are significantly enhanced.

Effects of workpiece size on bending angle in laser forming of al 6061-T6 sheet

In the laser forming process, the effect of workpiece size, including variations in width and length, plays a crucial role in determining product quality. To better understand the deformation behavior and obtain the desired bending angle with varying workpiece sizes, the size effect on laser forming of Al 6061-T6 aluminium alloy has been investigated. Due to the fact that Al 6061-T6 alloy sheets have more deformability and high strength properties, they have been studied in this paper. A three-dimensional numerical model that considers temperature-dependent properties of the material, and convection-radiation heat losses is constructed to investigate the sheet deformation. The numerical model is verified by performing experimental tests under the considered operating conditions. The suggested model is found to be in reasonable agreement with the experimental findings, and it is shown to have a maximum error less than 8 % when predicting the bend angle. Computed results through the numerical model show that the bending response is increased with the increase in workpiece width; however, it is marginally affected with workpiece length. Based on simulation results, the edge effect is also explored in relation to workpiece size. Edge effect increases as sheet width increases; whilst it decreases as sheet length increases. This investigation will be helpful in laser-based forming industries for obtaining desired bending of Al 6061-T6 sheets.

Microstructure evolution and strengthening mechanisms of high strength Al-Zn-Mg-Cu alloy via pre-hardening forming

The precipitating and strengthening behavior of the pre-hardening forming (PHF) process for a high-strength Al-Zn-Mg-Cu alloy is studied. The PHF process obviates the need for artificial aging (120 °C for 24 h) during hot forming. Despite the considerably lower volume fraction of η' (with a maximum of 0.54 %) in the PHF samples compared to that of the T6 samples, the maximum yield strength of the 12 h-5 min tensile specimen is 496 MPa, similar to that of the T6 alloy (490 MPa). It is assumed that the GPII zones have compensated for the insufficient yield strength in PHF samples. Through the integration of small-angle X-ray scattering (SAXS) experiments and the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equations, the strengthening effects attributable to GPII zones and η' have been discerned. Intriguingly, the contribution of GPII zones to yield strength (219 MPa in the 12 h-5 min sample) equals that of η' (167 MPa in the 12 h-5 min sample). A comprehensive yield strength model is subsequently established, including both GPII zones and η' phase, exhibiting a deviation between fitting and experimental results of less than 5 %.

Analysis of the Combine ECAP's Heat Treatment for Creating Aluminum Chips, as Well as a Correlation and Regression Analysis of the solid-state data

The primary objective of this study is to provide a green solution for aluminum recycling. For the aluminum industry to become more circular, it is crucial that innovative recycling methods be developed to maximize the potential for scrap reuse and reduce CO2 emissions. In this article, we discuss how energy and material costs were reduced by recycling aluminum chip waste without first remelting the chips. Solid state recycling or direct recycling are common terms for the method shown here. Chips are cleaned, cold pre-compacted, and hot direct extruded in the solid state recycling process. This is followed by equal channel angular pressing (ECAP) and heat treatment. The effect of artificial aging time and temperature, as well as holding time during solid solution treatment, on the mechanical characteristics of recycled EN AW 6082 aluminum chips was studied. The studies were carried out using a response surface methodology and a design of experiments strategy. The effect of changing the settings of the heat treatment for the proposed solid state recycling process on the mechanical properties of the recycled samples was modeled using a regression analysis. When compared to commercially manufactured EN AW 6082 aluminum alloy in T6 temper condition, the mechanical properties of the recycled samples obtained using the innovative process were found to be comparable. The recycled samples were also analyzed using metallography. Models using regression and correlation analysis have been created to describe the impact of heat treatment settings on the mechanical properties of the generated samples reported in the statistical analysis. using MATLAB as analytical program to conduct correlation and regression.

Microstructural evolution and corrosion mechanism of micro-alloyed 2024 (Zr, Sc, Ag) aluminum alloys

The 2024 aluminum alloy has excellent mechanical and low corrosion due to the existence of the high Cu levels, which shortens its service life. In this paper, we have systematically investigated the mechanism of the influence of three elements (Sc, Zr, and Ag) on the microstructure and corrosion behavior of 2024 aluminum alloy after microalloying. The results showed that microalloying treatment of 2024 aluminum alloy reduced the dendritic spacing of cast aluminum alloy; decreased the sizes of Cu-rich intermetallic particles (Cu-IMPs) within the peak aging of the T6 alloy to make their distribution more uniform; and changed the grain boundary phases (GBPs) and precipitate-free zones (PFZs) width of the T6 alloy. Microalloying treatment significantly changed the corrosion resistance of the alloy. Both Zr and Ag elements significantly improved the corrosion resistance of the alloy and reduced IGC depth and electrochemical corrosion rate, however, the Sc elements deteriorated the corrosion resistance of the alloy. Moreover, the corrosion mechanism of the alloy was also discussed in detail.

Alumoxane film for corrosion protection of 2024 aluminum alloy

Alumoxane film on anodized 2024 was obtained using stearic acid to prevent corrosion in a chloride medium. A cleaning pretreatment was applied to the metal surface to improve the adhesion and formation of the alumoxane film using three different sprays, ethanol, water, and NaOH. Then a molten stearic acid was applied to form an alumoxane. The obtained films were characterized by X-ray photoelectron spectroscopy and glow discharge optical emission spectroscopy, and electrochemical techniques, such as linear sweep voltammetry and electrochemical impedance spectroscopy, evaluated the corrosion protection. The surface analyses suggested an interaction between the boehmite and stearic acid to form alumoxane, and the electrochemical results revealed that alumoxane film using ethanol significantly improved the protection against corrosion due to the formation of compact and homogeneous films with a hydrophobic characteristic for the 2024-T3 alloy.

Effects of different profiled pins used in friction stir welding of Al 6061 T6

Abstract In this study, Al 6061 T6 alloy was joined by friction stir welding method with the same parameters using with different profiled pins. As a result of the experiments carried out, the samples were subjected to metallographic examination, hardness measurements, tensile test and bending test. As a result of the examinations carried out, changes in welding performances were determined with the change of pin profiles. As a result of these changes, it was determined that the pin profile suitable for the applied welding parameters was pyramid. It has been concluded that in the use of triangular profile pins, the welding parameters in question should be higher, and the most important reason for this is that the stir zone is larger.

Orthogonal impact load in 6061-T651 and 7075-T651 aluminum alloy plates

Orthogonal impact load in 6061-T651 and 7075-T651 aluminum alloys was evaluated. Clamped square plates with the dimensions of 300 × 300 × 6.35 mm were experimentally impacted at 200, 400 and 600 J with different velocities by means of a drop tower-device. Impacted force-time and -displacement curves were obtained to evaluate the absorbed energy. Also, the impact damage was evaluated in terms of the transverse displacement and overall crack length induced to the plate. Further, explicit finite element and analytical approaches were used to compare against the experimental results. Considering the absorbed energy as a direct function of the induced damage, it was observed that the 7075-T651 alloy had a better performance than 6061-T651 for the 200 J impact test. Even though both alloys had a similar response for the 400 J impact test, it was not the case at 600 J where the absorbed impact energy for the 6061-T651 alloy was higher than for the 7075-T651. The induced damage (crack length) tends to increase with the strain rate for a given impact energy level.

The Behaviour of Hybrid Aluminium-Steel Resistance Spot Welded Joints in Case of Dynamic Loading

Hybrid joints between aluminium and steel are used sometimes in case of thin sheets for example for a car body. Resistance welding for this joining challenge is not frequently used, but the resistance welded joints basically have good mechanical properties. During resistance spot joining of these hybrid joints, fusion between the two materials cannot occur, but with the right technological parameters an intermetallic compound (IMC) appears in the joint line. The properties of the IMC have significant effect to the joint properties, because the researchers basically investigate this. The original static mechanical tests can show good, comparable results for the joint properties. If we see the dynamic tests basically really difficult to find results in case of spot welding of steels and joining of hybrid aluminium – steel joints. The aim of this paper to show the dynamic properties of these hybrid joints. During our investigation DP600 dual-phase steel was used as the steel part because this grade is frequently used in a car chassis. For the aluminium part, two types of aluminium were applied: non-heat treatable 5754-H22 alloy, and heat-treatable 6082-T6 alloy. The different aluminium alloys have different properties, so different technological parameter combinations were used. To test the resistance of hybrid joints against dynamic loading, instrumented impact tests were performed. This special impact test is considered as an impact-bending test, because the load is perpendicular to the welded point joint. Force – time diagrams of impact tests were shown too in this paper. The intermetallic compound is necessary for joint, but it is very brittle with very big hardness, but in case of dynamic testing this hardness has no significant effect, so these specimens show good result in case of dynamic loading. The two different aluminium – steel joints show different resistance against dynamic loading, and the fracture modes were different too.

Modifying the microstructure and stress distribution of crossover Al-Mg-Zn alloy for regulating stress corrosion cracking via retrogression and re-aging treatment

For next-generation high-performance Al alloys, stress corrosion cracking (SCC) under the combined action of anodic dissolution and hydrogen embrittlement has been a long-standing problem. Herein, a novel SCC-resistant Al alloy design strategy that maintains high strength by optimizing the microstructure and microstress distribution is proposed and developed. Results demonstrated that stress corrosion cracks sprouted and expanded along stress concentration regions. In a T-phase strengthened crossover Al–5.0Mg–4.0Zn alloy, minimal stress concentrations at the grain and phase boundary improved the SCC resistance by high-temperature retrogression and re-aging treatments. Compared with the T6 alloy, the high-temperature retrogression RRA435 °C alloy reduced stress concentration by 36.7% and decreased the diffusion rate of H atoms by 81 folds. The improved SCC resistance was primarily attributed to the reduced diffusion coefficient of hydrogen because of the minimal stress concentrations.

Fatigue behavior of notched and unnotched 7075-T6 aluminum alloy subjected to retrogression and re-aging (RRA) heat treatment and plasma nitriding

Aluminum alloys are widely used in aircraft components, which present the fatigue process as one of the main failure modes. The aeronautical industry has been searching for alternatives to increase the service life and safety of structural components. To address this issue, this work subjected the 7075-T6 alloy to retrogression and re-aging (RRA) heat treatment and plasma nitriding in order to obtain an improvement in the corrosion resistance. The objective was then to evaluate whether such treatments affected the fatigue behavior. Fatigue tests were carried out on the material with a smooth surface and with a notch (theoretical stress concentration factor of 5.7). A maximum likelihood estimation method was used to estimate the S-N curve parameters. The fatigue behavior without notch for the T6 and RRA treatments was similar, which is expected because the resulting microstructure of the RRA condition is composed of a homogeneous distribution of very fine η’ precipitates in the aluminum matrix, similar to the T6 condition. The worst fatigue behavior without notch was found for the material underplasma nitriding for two main reasons: the softening of the microstructure after processing and the substantial increase of the surface roughness. Regarding the notched material, the fatigue performance was reduced to a similar level regardless of the condition.

Effect of pH on wettability properties on aluminium alloy surfaces treated with direct laser writing

Nowadays, lightweight materials become more important in diverse industrial applications, such as automotive and aeronautics. Innovative surface features like superhydrophobicity enable further fields of applications. In this context, aluminium Al 2024-T351 alloy is structured using direct laser writing (DLW) to achieve a superhydrophobic surface. To address the effect of pH on the superhydrophobic behaviour, the static contact angle (SCA) is measured at different pH values (pH 1, 2, 4, 7, 9, 11 and 14), in comparison to a non-structured reference sample. The results show that superhydrophobic state in DLW samples is preserved in the pH range 2 – 9 with SCA between 151.1 ± 1.5° and 157.0 ± 0.5°. While stable hydrophobicity is still observed at pH 1, the samples exposed to pH 11 and 14 solutions exhibit collapse in the droplet and a fast chemical reaction, respectively. Concerning the non-structured samples, SCA is lower at pH 4, 11 and 14 than at neutral pH 7. This effect can be rationalized considering dealloying of Al2CuMg precipitates present in the surface of Al 2024-T351 alloy. Differences between non-structured and laser structured samples can be explained taking into account the change in present phases after laser ablation.

Effect of natural aging on the tensile properties and the toughness of friction stir welds of 2024-T3 aluminum alloy

During friction stir welding of metallic alloys, four different microstructure zones are formed in the weld, resulting in heterogeneous mechanical properties in this latter. In the case of aluminum alloys, these properties are bound to change with aging, whether natural or artificial. In this study, changes in the toughness and tensile behavior of friction stir welds in Al 2024-T3 alloy over time are investigated. Only specimens found to be defect free, by X-ray imaging, are tested. Characterized by the area under the stress-strain curve of the material, the toughness is found to be 19% lower after 24 months of natural aging. This decrease in toughness is mainly due to a loss of ductility as the elongation of the material drops by 27% while the ultimate tensile strength increases by 9%. The fracture zone and pattern remain the same for both natural aged and freshly welded specimens. These results can be used to estimate the service life of structures using such a material, as in aeronautics.

Research of Friction Stir Welding (FSW) and Electron Beam Welding (EBW) Process for 6082-T6 Aluminum Alloy.

The paper presents the results of the joining tests of the EN AW-6082 T6 alloy. The materials were joined using the EBW high-energy (electron beam welding) and friction stir welding (FSW) methods. In the case of FSW welding, the following parameters were used: the linear speed was 355 mm/min, and the rotational speed of the welding tool was 710. In the case of EBW welding, the following parameters were used: accelerating voltage U = 120 kV, beam intensity I = 18.7 mA, welding speed v = 1600 mm/min and, in the case of a smoothing weld, U = 80 kV, beam intensity I = 17 mA, and welding speed v = 700 mm/min. Comprehensive microstructural tests of all welded joints (MO, SEM and TEM) and mechanical property tests (tensile and hardness tests) were carried out. The topographies of the fractures after the tensile test were also examined. Based on the results, it was found that the strength properties of the EBW joint were reduced by 23% and the FSW joint by 38% compared to the base material. A decrease in elongation was also noted, with an FSW elongation of 7.2% and an elongation of 2.7% for EBW. In the case of the EBW joint, magnesium evaporation was found in the weld during welding, while in the FSW joint, the dissolution of the Mg2Si particles responsible for strengthening the material during heat treatment to the T6 state was observed.

Scaled fatigue cracks under service loads

Scaled experimentation is a powerful engineering tool yet its application to fatigue is limited by significant changes in behaviour with scale. The recent discovery of new similitude rules however opens new possibilities that are explored in this work through numerical experimentation for industrially representative fatigue-crack growth scenarios. It is shown for the first time, how the geometric size effects present in mixed mode fatigue tests are eliminated by performing two appropriately designed scaled experiments. The first order finite similitude theory is applied to mixed mode (modes I and II) fatigue crack growth in three case studies, viz., compact tension shear (CTS) specimen, wing fuselage attachment lug, and a T-joint with an inclined semi elliptical crack. Both planar and non-planar crack growth feature, along with surface and through thickness cracks. Low and high cycle fatigue (up to circa 60,000 cycles) is examined for three different materials (Al-6061 T6 alloy, structural steel, and AISI 316 stainless steel) under a variety of load ratios. The new rules return near exact crack-path predictions whereas lifecycle predictions have errors ranging between 1 % and 9 %. Paris law constants C and m are predicted with up to 99.9 % accuracy supporting the theory that Paris law is a first order similitude rule. Geometric size effects afflicting industrial type scaled-fatigue studies employing a damage tolerant design approach are confirmed to be eliminated on combination of information from two appropriately designed scaled models.

Effect Mechanism of Sc Addition and T6 Heat Treatment on Precipitated Phase and Mechanical Properties of Al‐Cu‐Mn Alloy

The microstructure and mechanical properties of cast Al‐Cu‐Mn alloy influenced by various Sc additions (viz. 0.1, 0.2, 0.3, 0.4, and 0.5 wt%) are investigated. It is found that the grain size of α‐Al and the area proportion of the second phase are decreased with the addition of Sc. In addition, the morphology of the precipitated phase in Al‐Cu‐Mn alloy also evolves at different stages, and the solidification temperature range and initial enthalpy change of the alloy are changed, resulting in the formation of a variety of second‐phase containing Sc. Owing to the grain refinement and precipitation strengthening effects, the hardness of as‐cast alloys is better than T6 alloys. Moreover, it is observed that when the Sc content is 0.3%, the mechanical properties of the as‐cast Al‐Cu‐Mn alloy are the minimum, and the Al‐Cu‐Mn alloys after T6 heat treatment are the maximum. These results confirm that the mechanical properties improvement effect of the as‐cast Al‐Cu‐Mn alloy is greater than that of the T6 heat treatment Al‐Cu‐Mn alloy with the addition of Sc. Meanwhile, the Orowan strengthening mechanism is found to have lost its dominant position.