Aged Aluminum Alloy Research Articles

Strain-induced clustering in Al alloys

Solute clusters represent the start of decomposition during aging of aluminum alloys and can generate strengthening while keeping the strain hardening high in comparison with shearable precipitates. In this study, clusters in a pre-aged AlMgSiCu 6xxx-series and a recently developed AlMgZnCu crossover alloy were investigated by atom probe tomography (APT) and tensile testing before and after straining. Pre-aging was performed at 100 °C and 60 °C respectively, and a tensile strain of 5% was applied. The key feature detected was the formation of clusters during plastic deformation, referred to here as “strain-induced clustering”. It is explained based on diffusion enhancement by the strain-induced formation of excess vacancies during tensile testing, and evaluated by means of a simple modeling approach. In addition to the significant intrinsic contribution of clusters to strain hardening via dislocations, strain-induced clustering adds a hypothetical non-dislocation-based component to strain hardening.

Validation of on-line crack compliance data analysis methods for the residual stress intensity factor

Residual stress can significantly impact the fatigue crack growth rate (FCGR) observed in standard tests. In the present study, implementation of the on-line crack compliance (OLCC) method for determining the residual stress intensity factor, Kres, in FCGR tests is supported by validation data, details of novel data analysis methods, and strategies for data reduction. Slitting measurements on C(T) specimens of quenched (but not stress relieved) and aged aluminum alloy 7050-T74 provide reference profiles of Kres as a function of crack size. The OLCC method quantifies Kres profiles from stress intensity factor control and load control FCGR tests over a range of residual stress states. Novel OLCC data reduction techniques are developed, and data analysis attributes and limitations explored, contributing to an improved methodology for standardization. The results demonstrate that the on-line crack compliance method is a valid means of quantifying Kres during fatigue crack growth rate testing.

Multiaxial ductile fracture criteria coupled with non-quadratic non-prismatic yield surface in the predictions for a naturally aged aluminium alloy

Multiaxial ductile fracture criteria coupled with non-quadratic non-prismatic yield surface in the predictions for a naturally aged aluminium alloy

Influence of adjusting the anodizing and aging sequences on the microstructure, fatigue property and corrosion resistance of anodized AA6082 alloys

Compared with the traditional anodization of aged aluminum alloy, a novel process was carried out by anodic oxidation of solid solution aluminum alloy, followed by aging treatment to optimize the interface's composition and microstructure, under which the thickness, hardness and modulus of the oxidation film wouldn't be influenced and the strength of base materials kept the same. As β” precipitates cannot be formed in the subsequent aging process due to the consumption of Mg on the film-base interface, line defects caused by lattice distortion were avoided. Therefore, the stress concentration point in the fatigue process was reduced, and the fatigue property of the anodized material was improved from 89 MPa to 125 MPa. The anodizing of solid solution aluminum alloy helps the dispersion of Mg in the oxide film, which increases the self-corrosion potential of the oxide film from −0.97 V to −0.32 V and delays the occurrence of pitting corrosion during long-term immersion in 5 wt% NaCl solution.

Influence of the Intensity of a Constant Magnetic Field on the Process of Phase Formation in an Aged Aluminum Alloy Al–Si–Cu–Fe

Influence of the Intensity of a Constant Magnetic Field on the Process of Phase Formation in an Aged Aluminum Alloy Al–Si–Cu–Fe

Influence of tool pin profile on mechanical and metallurgical behavior of friction stir welded AA6061-T6 and AA2017-T6 tailored blanks

The heat-treated and artificially aged aluminium alloys of AA6061 and AA2017 are friction stir welded by employing five different tool pin profiles keeping the other process parameters constant. From this investigation, the mechanical properties of welded blanks were evaluated. The test results revealed that the straight square tool pin profile exhibited a higher ultimate tensile strength of 253 MPa with a tensile elongation of 6.7%. Higher Microhardness and joint efficiency were reported compared to other pin profiles. The microstructures at different zones of the welded joint were examined using optical and scanning electron microscopy. More Flowability indications with fine grain structure were examined for a straight square tool pin profile. The presence of intermetallic and the formation of fine-grain structures were accountable for the improvement in microhardness. The pulsating action of the square pin profile produced a defect-free joint.

Residual stress investigation of quenched and artificially aged aluminum alloy 7175

Residual stress investigation of quenched and artificially aged aluminum alloy 7175

Research on compression deformation behavior of aging AA6082 aluminum alloy based on strain compensation constitutive equation and PSO-BP network model

It is important to model the flow behavior of an aged aluminum alloy AA6082 as an extrusion material before design and optimize of the forming process. In this study, the isothermal compression tests were carried out on Gleeble-3800 thermal simulator in the temperature range of 423−773 K and the deformation condition of 0.01–1.0 s−1 to study the cold temperature and hot deformation behavior of aluminum alloy AA6082. Considering the experimental error, the discussion based on friction and temperature correction is carried out. According to the modified data, based on the traditional Arrhenius constitutive model, a method combining the strain compensation Arrhenius model and PSO-BP neural network was proposed to describe the flow behavior of aluminum alloy AA6082. The prediction ability and stability of the model are evaluated by using the linear correlation coefficient(r), the average relative errors (AARE), the Root mean square errors(RMSE) and the relative errors (RE) in statistical analysis. The results show that the 3-10-8-1 double hidden layer neural network model based on PSO-BP has higher effect in predicting the flow characteristics of aging aluminum alloy AA6082 than that of Arrhenius model based on strain compensation. The linear correlation coefficient, mean relative error and root mean square error are 0.9996 %, 2.001 % and 1.665 MPa respectively.

Structural And Mechanical Response of Artificially Aged Aluminum Alloy 6061

Structural And Mechanical Response of Artificially Aged Aluminum Alloy 6061

Multi-Criteria Optimization of Aerospace Alloys in WEDM Using TOPSIS

Wire EDM is commonly used for machining of complex profiles in hard and exotic materials. In the present work the key performance of Wire EDM such as wire cutting speed, surface roughness and cut width in machining of three different aerospace class materials such as near beta titanium alloy, forged nickel base alloy and aged aluminum alloy are studied. Apart from electrical parameters, the wire with zinc coated brass and plain brass are used. TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) is the Multi-Criteria Decision-Making method used for selecting the best setting of control parameters. Parameter sets are ranked from best to worst based on the performance score. Zinc coated wire outperforms the brass wire almost for every response variable in case of Ni and Ti alloy while with Al it is as good as plain wire.

Simulation of Microstructure Evolution in Metal Materials under Hot Plastic Deformation and Heat Treatment

The development of modern computational techniques and equipment enables one to perform high-precision calculations of complex processes for industry, including metallurgy. This review has classified the basic physical and mathematical models of structure formation during heat and deformation treatment. The Kocks–Mecking–Estrin model describing the dislocation structure at the initial stage of hot plastic deformation has been analyzed. The models of dynamic, metadynamic, and static recrystallization kinetics based on the Johnson–Mehl–Avrami–Kolmogorov equation have been considered. The models of the kinetics of phase transformation upon heating and cooling of steel have been reviewed. The Kampmann–Wagner model that describes the decomposition of supersaturated solid solution during the aging of aluminum alloys has also been considered. The main computational techniques to calculate microstructural evolution, such as the cellular automaton, Monte Carlo, and multiphase-field techniques have been considered. They exhibit high accuracy when calculating recrystallization processes and phase transformations. The systematization of the existing models that describe structural evolution has revealed the possibility to develop complex models for the comprehensive calculation of full cycles to process metal materials by heating and deformation. These models can be used for the optimization and development of new processing techniques.

A Constitutive Model for Yield Strength and Work Hardening Behaviour of Aluminium Alloys during Artificial Ageing

In this study, a unified constitutive model has been developed for both yield strength and work hardening behaviour prediction of aluminium alloys with different types of precipitates during and after artificial ageing. The different type and dimensions of general precipitate shapes (sphere, plate, rod) have been classified and modelled by a primary dimension and aspect ratio, with which a general set of equations has been utilised to model the precipitates evolutions during ageing of various aluminium alloys. In addition, the effects of main microstructures on not only yield strength but also work-hardening behaviour of artificially aged aluminium alloys have been considered and modelled, based on which, a whole set of unified constitutive model considering both micro- and macro-properties for long-term artificial ageing of aluminium alloys has been proposed. Artificial ageing of two representative aluminium alloys (an Al-Mg-Si alloy AA6063 and an Al-Cu-Li alloy AA2198) has been adopted to show the capability and effectiveness of the developed model. The results show that the model can successfully predict the microstructures, yield strength and work hardening behaviour of various aluminium alloys with different precipitate types after long-term artificial ageing process, e.g., from 0 h to 500 h. It is believed that the model can be used for ageing of other aluminium alloys with dominant sphere, plate or rod-shaped precipitates.

Synergistic effect of CeCl3 and benzotriazole on corrosion resistance of naturally aged and artificially aged AA2024 aluminium alloy

Abstract The corrosion behaviours of naturally aged and artificially aged AA2024 aluminium alloys in 0.5 mol/dm3 NaCl solution in the presence of environmentally friendly corrosion inhibitors of 10 mmol/dm3 CeCl3, 10 mmol/dm3 BTA and the inhibitor mixture (5 mmol/dm3 CeCl3 + 5 mmol/dm3 BTA) were analyzed. The goal of this work was to determine the level of the synergistic effect of the inhibitor mixture and to explain the nature of this effect. Corrosion properties of the inhibitor layer were studied using the electrochemical impedance spectroscopy (EIS), while the resistance to pit formation and pit growth was studied by applying potentiodynamic polarisation tests. The results of scanning electron microscopy (SEM/EDS) showed that the size of pits formed in naturally aged aluminium alloy was smaller than that formed in artificially aged alloy. The synergistic effect of the inhibitor mixture on corrosion properties of naturally aged alloy was observed throughout 96 h, and in later phases of testing of artificially aged alloy. The synergistic effect of the inhibitor mixture was not noticed on pit formation and pit growth.

Resistance to Pit Formation and Pit Growth for Different Tempers of AA2024 Aluminium Alloy in Presence of Benzotriazole

The paper analyses the corrosion behaviour of both naturally and artificially aged AA2024 aluminium alloy in NaCl solution in the presence of the corrosion inhibitor benzotriazole (BTA). The differences between these two aging tempers in terms of resistance to general corrosion are explained as well as the differences in terms of pit formation and pit growth. Based on the values of the polarisation resistance and the corrosion current density, the general corrosion resistance of the alloy is determined in the absence and in the presence of BTA. The resistance to pit formation and pit growth is determined on the basis of the polarisation measurements results. Scanning electron microscopy confirmed the expected differences in the appearance and size of the pits formed in naturally aged and artificially aged alloy. In the presence of the corrosion inhibitor BTA, for both aging tempers of the alloy, the corrosion resistance is significantly higher compared to the resistance in the solution without the inhibitor. The value of the polarisation resistance for both aging tempers increases over time. However, at the same time, the value of the constant phase element increases as well. An explanation for this phenomenon is provided. The calculated average value of the thickness of the adsorbed inhibitor layer on the surface of the aluminium alloy is in accordance with the inhibitor protective ability for both aging tempers.

Work hardening and plastic anisotropy of naturally and artificially aged aluminium alloy AA6063

The plastic anisotropy of an extruded AA6063 alloy after different heat treatments was investigated in a previous study by Khadyko et al. (2017). The material was available in temper T1 (naturally aged to a substantially stable condition) and directly heat treated to the peak aged, overaged and soft annealed conditions without solution heat treatment. Tensile tests in different material directions were performed for these materials and it was found that the plastic anisotropy depended in a complex way on the heat treatment. In the present study, the experimental programme is extended to investigate further the influence of heat treatment on the plastic anisotropy. The AA6063 extruded alloy is first solution heat treated, and then either naturally aged to temper T4 or artificially aged to tempers T6 (peak aged) and T7 (over-aged). Tensile tests in three material directions are performed for these tempers and in the solution heat treated condition (temper W) to reveal the plastic anisotropy. The microstructure evolution of all these materials is then modelled using a nanostructure model (NaMo), which predicts the size distribution of hardening particles, the solute content, the yield strength and the work hardening. The predictions of NaMo are validated using the available data from the tensile tests and TEM observations, and used to analyse the correlation between the stress-strain behaviour and the heat treatment and microstructure of the different materials.

Precipitate Evolution and Fatigue Crack Growth in Creep and Artificially Aged Aluminum Alloy

The fatigue performance of high-strength Al-Cu-Mg alloys is generally influenced by the process of creep age formation when applied to acquire higher strength. The results show that creep aging accelerates the precipitation process, leading to a more uniform precipitation of strengthening phases in grains, as well as narrowed precipitation-free zones (PFZ). Compared with the artificially aged alloy, the yield strength and hardness of the creep aged alloy increased, but the fatigue resistance decreased. In the low stress intensity factor region (ΔK ≤ 7 MPa·m1/2), the fatigue crack propagation (FCP) rate was mainly affected by the characteristics of precipitates, and the fatigue resistance noticeably decreased with the increased creep time. In a 4 h creep aged alloy, the microstructure was dominated by Cu-Mg clusters and Guinier-Preston (GP) zones, while S″ phases began to precipitate in the matrix, showing better fatigue resistance. After aging for 24 h, the needle-shaped S’ phases were largely precipitated and coarsened, which changed the mode of dislocation slip, reduced the reversibility of slip, and accelerated the accumulation of fatigue damage. In stable and rapid crack propagation regions, the influence of precipitates on the FCP rate was negligible.

Atomistic insights into cluster strengthening in aluminum alloys

In certain naturally aged aluminum alloys, significant strengthening can be obtained due to the decomposition of a super-saturated solid solution into clusters. The origins of such strengthening remain unclear due to the challenge of differentiating solute cluster strengthening from solid solution or precipitate strengthening. To shed light on the origin of cluster strengthening in aluminum alloys, the interaction between the smallest possible type of clusters (i.e. dimers) and moving dislocations in a model Al–Mg alloy is studied using atomistic simulations. Additionally, theoretical models for both the parelastic and dielastic interactions between clusters and dislocations is used to identify which factor among order strengthening, elastic interaction, and change of stacking fault energy controls cluster strengthening. The comparison of the results from these models to that of the atomistic simulations show that in the case of Mg dimers, the strength of the strongest ones are dominated by the dielastic contribution through the change of stacking fault energy.

Influence of Potential Scan Rate on Corrosion Behaviour of Heat Treated AA 7075 Alloy in Sulphuric Acid Solution

In this paper, the effect of scan rate on the corrosion parameters and electrochemical behaviour of Retrogression and Re-aging (RRA) heat treatment of 7075 aluminium alloy has been investigated by Potentiodynamic polarization (PD) and electrochemical impedance spectroscopy (EIS) methods. The Potentiodynamic polarization (PD) curves were obtained at various scan rates for aged aluminium alloys in 0.5 M H2SO4 solution. The results show that at high scan rates shows unpredicted fluctuation of charging current, whereas at lower scan rates fewer disturbances are observed. The aged samples were chemically and mechanically characterized. It was observed that the RRA at 0.7 h shown improved corrosion property as well as mechanical properties compared to T6 temper. The corrosion properties were confirmed by EIS and polarization experiments.

Evolution of dislocation patterns inside the plastic zone introduced by fatigue in an aged aluminium alloy AA2024-T3

The formation of dislocations patterns within the plastic zone ahead of a crack tip introduced by fatigue loading in AA2024-T3 sheets is studied by electron channelling contrast imaging (ECCI) and electron backscatter diffraction (EBSD). The aim lies in correlating local plastic effects at grain level with digital image correlation (DIC) results obtained at coarser resolution. While dislocation patterns are observed already prior to fatigue loading, the presence of dislocation sources and dislocation entanglements increases towards highly deformed regions near the crack path. Also, deformation veins are revealed by EBSD in grains located along the crack path. Based on ECCI and EBSD the dislocation density was determined and shows a gradient towards the crack tip. The results help linking the process of fatigue deformation at grain-level to the deformation field probed at the meso-scale level.

EFFECT OF DISPERSED PHASE COMPOSITION AND DISTRIBUTION AFTER AGING ON FORMABILITY OF D16 ALUMINIUM ALLOY SHEETS

The relevance of this paper is connected with rising accuracy requirements to stamped parts made of aged aluminium alloys applied also for layered composite making. These requirements can be met by controlling the sheet blank structure, and particularly its phase composition. The paper provides experimental results obtained when studying the effect of aging modes on the composition, dispersed phase distribution pattern and formability of sheet samples made of D16 (AA2024) aluminium alloy. Heat treatment consisted in quenching from a temperature of 500 °С into room temperature water and further aging: natural aging during 7 days, artificial aging at temperatures of 50, 100, 150 and 200 °С and holding at each temperature during 15, 30, 60, 120 and 240 minutes. The quantitative method is proposed to evaluate the dispersed phase distribution pattern by microstructure pictures. Formability was evaluated using the stamping number, i.e. a proof/ultimate factor. It was found that the stamping number rises as the aging temperature and holding time are increased, which shows the lower alloy applicability for sheet stamping operations. No dispersed phase was formed when aged at t = 50 °С in both optical metallography and scan electron microscopy cases. The non-uniformity of dispersed phase distribution inside a grain rises at initial aging stages with a holding time less than 1 hour at 100, 150 and 200 °С and decreases with a further increase in the holding time up to 4 hours. No correlation was observed between the uniformity of phase distribution and the stamping number. The chemical composition of phases has a greater effect on the formability and changes depending on a heat treatment mode: annealing and natural aging primarily lead to the θ and S phase precipitation; aging at temperatures below 150 °С with a holding time less than 1 hour lead to the θ, S and T phase precipitation; θ phase appears after aging at temperatures over 150 °C with long holding times.