Rolled Aluminum Alloy Research Articles

In situ characterization of AA1050 recrystallization kinetics using high temperature nanoindentation testing

Static recrystallization kinetics, at 300 °C, of a hot rolled commercial purity aluminum alloy AA1050 has been investigated using high temperature nanoindentation. Annealing treatments were achieved inside a nanoindentation device to measure corresponding hot nanohardness versus time. Clear evidences of recrystallization phenomenon were deduced from both hardness decrease and pop-in events on load-displacement curves. The recrystallized fraction for increasing annealing time was compared to conventional post mortem characterizations – i.e. EBSD and Vickers hardness. A good agreement was found between in situ and post mortem characterization methods. High temperature nanoindentation is proved to be a powerful tool for fast characterization of materials' recrystallization kinetics.

Comparing Two Selection Laws of Active Slip Systems in Finite Element Polycrystalline Model for Numerical Material Testing

To meet the demand for high accuracy in metal forming simulation including difficult problems such as anisotropy, many material models have been developed. Since the recent material models usually possess many parameters and require cumbersome experiments, a reliable numerical material testing would be helpful to reduce the number of experiments. Therefore, we have engaged in development of a numerical material testing based on the finite element polycrystalline model in which the successive integration method is used for modeling slip systems. However, implementation based on the strain-rate dependent model, which is considered as the mainstream of such model, has not been rigorously considered in our research. In this study, two polycrystalline models were compared to establish better microstructural modeling for constructing a scheme of numerical material testing to predict material behavior that is not obtained by experiments. Numerical rolling, uniaxial tensile tests were conducted on aluminum alloy sheet with the strain-rate dependent model and the successive integration method. The crystal orientation calculated by the successive integration method exhibited close agreement with the experimental value of the rolled aluminum alloy sheet. On the other hand, the calculated crystal orientation by the strain-rate dependent model exhibited less close agreement with the experimental value of the same material than the successive integration method. To ascertain the characteristics of each model in terms of slip deformation quantitatively, the other tensile tests were conducted to calculate Lankford values caused by crystal orientation. Lankford values, calculated by the successive integration method, exhibited better agreement with experimental values than the strain-rate dependent model. These comparisons indicate that the successive integration method represented slip deformation more physically valid than the strain-rate dependent model and resulted in better calculation.

Microstructure evolution in the conventional single side and bobbin tool friction stir welding of thick rolled 7085-T7452 aluminum alloy

The microstructure evolution during the conventional single side friction stir welding (SS-FSW) and the bobbin tool FSW (BB-FSW) of 7085-T7452 alloy thick plate was extensively studied by using the state-of-the-art materials characterization techniques. The Electron backscattering diffraction results reveal that a significant grain refinement and a larger percentage of high angle grain boundaries (HAGBs) exist in the weld nugget zone (WNZ) and the thermal-mechanical affected zone (TMAZ) compared with the base material. Meanwhile, more obviously inhomogeneous refined grains and HAGBs in WNZ along the thickness direction and a larger percentage of low angle grain boundaries (LAGBs) were observed in SS-FSW joint than that in BB-FSW joint. The change of the average grain size is the result of friction heat and strain rate of plastic deformation combined with a certain degree of recrystallization. Moreover, the recrystallization is mainly controlled by the strain rate during the FSW process. The presence of Cube and Cube ND after welding shows that the discontinuously dynamic recrystallization (DDRX) is a major factor in the final microstructural response. The research and findings help the understanding of the mechanism of microstructure homogenization and further optimizing the welding process for application.

A macroscopic strain-space model of anisotropic, cyclic plasticity with hardening

We present a strain-based formulation of macroscopic plastic deformation that accounts for anisotropy in both the initial yielding and subsequent hardening. Both isotropic and kinematic hardening are considered. Thus the model captures the evolution in the deformation response on cyclic loading including the Bauschinger effect, and the accumulation of plastic strain (ratcheting response). The model is formulated in the strain space and implemented using an implicit time integration scheme. The capabilities of the model are demonstrated through material parameter studies and by calibrating the model to experimental data for uniaxial tensile loading of Inconel alloy and anisotropic yielding of rolled aluminum alloy sheets. We also show that this strain-based approach is equivalent to the more traditional stress-based approach. The strain-based formulation of this model makes it attractive for coupling with other strain-based phenomena like phase-transformations in shape-memory alloys and failure.

English

The goal of this project is to investigate the Residual Stress in hot rolled aluminium alloys where both experiments and computer simulation will be implemented in order to get highest degree of investigation. This project is a miniature investigation process of real problem faced by AIRBUS, in the field of failure of wings against superfluous residual stresses. The residual stress level achieved from simulation matches to what received from the hole-drilling measurement after quenching process, hence, the necessity of the complex and expensive hole-drilling method can simply be omitted in the real industry resulting huge time saving in mass production units.

Effect of accumulative roll bonding process on textural evolution and its comparison with normal rolled AA7005 aluminum alloy

In the present work, texture evolution of AA7005 aluminum alloy during the accumulative roll bonding and conventionally rolled was investigated by X-ray diffraction. It was found that the dominant texture components of both samples were Brass, Copper, Rotated Cube and Goss components, but the ARB texture evolution was quicker and displayed complex features. When the number of ARB cycle increased, the intensity of texture components decreased at the second and third pass, then enhanced at the fourth pass, and finally decreased. During the ARB process there was a texture transition at the second and third pass from Brass and S to Rotated Cube components due to the shear texture which formed on the surface region and moved to the center during the next pass. The enhancement of texture intensity at the fourth pass might be attributed to the formation of nano shear bands. The texture intensity decreasing at final cycle was correlated to redundant shear strain and continuous recrystallization during the high ARB passes.

Anisotropic thermomechanical behavior of AA6082 aluminum alloy Al–Mg–Si–Mn

Abstract Hot rolled aluminum alloy 6082 was subjected to tensile tests and coefficient of thermal expansion measurements. These tests were realized in order to investigate the effect of direction on its anisotropic behavior. Specimens for both tests were cut in three directions (long transverse, longitudinal rolling and short transverse) with respect to rolling direction. Results showed that the longitudinal rolling and long transverse directions had limited effect on thermomechanical properties as compared to the short transverse direction. It was found that the short transverse direction exhibited higher values of stress hardening capacity and thermal expansion coefficient, lower ductility and dilatation, than the longitudinal rolling and long transverse directions. Thermomechanical anisotropy was attributed to the microstructure and precipitation behavior. It was assessed by means of tensile tests, coefficient of thermal expansion measurements, optical microscopy, X-ray diffraction and differential scanning calorimetry techniques.

Investigation of residual stresses distribution in equal channel angular rolled aluminum alloy by means of the slitting method

Equal channel angular rolling is a severe plastic deformation process which produces an ultrafine-grained structure and improves the mechanical properties of the samples. In this article, using the slitting method experimentally and finite element simulation, the residual stress distribution in an equal channel angular rolled Al alloy 5083 specimen was investigated. First, by applying the slitting technique on the considered specimen, the produced strains were measured and recorded. Then by employing the series expansion method, the through-thickness residual stresses were calculated. The compliance matrix was obtained by means of finite element analysis and 16 terms of the Legendre polynomial (L2 through L17) were used to get the compliance coefficients. According to the finite element results, the residual stresses were created in the sample because of different plastic strain deformation at the same times in different locations. The residual stress distribution was non-uniform and similar to sine curve. There was a good agreement between the obtained results by slitting method and finite element simulation.

Reactive mechanism and mechanical properties of in-situ hybrid nano-composites fabricated from an Al–Fe2O3 system by friction stir processing

In-situ Al/(Al13Fe4+Al2O3) hybrid nano-composite was fabricated using reactive friction stir processing (FSP) by introduction of Fe2O3 powder into the stir zone of rolled AA1050 aluminum alloy. Composite reinforcements were produced in-situ by exothermic reaction of Al and Fe2O3 that initiated by hot working characteristics of FSP. However, the existence of intermediate phase (Fe3O4) suggests that the reaction was not completed due to short time of FSP. EBSD results showed that the matrix mean grain size decreased to 8 and 3μm after FSP without and with introduction of powder, respectively; this was also associated with the marked increase in HAGB. The fabricated nano-composite exhibited superior hardness (45HV) and ultimate tensile strength (~171MPa) as compared to those of the base and FSPed alloy with no powder addition. Formation of in-situ reinforcements and grain refinement acted as major and minor contributors to enhancement of mechanical properties (hardness and ultimate tensile strength), respectively.

Three-dimensional mapping of the residual stress field in a locally rolled aluminium alloy specimen

Detrimental residual stresses that occur in welded joints can be removed by rolling the weld seam. In this study we show that rolling could be applied to much thicker-section welds than has previously been attempted. A residual stress field introduced by localised rolling of an aluminium alloy specimen was studied to establish whether the plastic deformation caused by rolling would be sufficient to treat thick-section welds. It was modelled using finite element analysis and characterised using detailed neutron diffraction measurements. During rolling, plastic deformation occurs through the entire thickness of the specimen and strongly compressive residual stresses are created in the rolled area. Some features of the three-dimensional residual stress field, such as a region of tensile stress beyond the end of the rolled area, could be detrimental to structural integrity. It is recommended that these should be taken into account in the design of rolling-based weld treatment and surface treatment processes.

Micro-scratching tests of a rolled aluminium alloy AA2024-T351 thick plate using a diamond micro-blade

The present research work is focused on investigating the apparent coefficient of abrasive friction of a rolled thick plate of an AA2024-T351 aluminium alloy, using micro-scratch tests. For this study, specific materials specimens and a particular UMT Micro-Scratch Equipment were used. The test involved the generation of a scratch process at a local scale using a diamond stylus (micro-blade defined by a radius of 0.8 μm) moving along a specified path under a constant normal force (10 N) and with a constant speed (0.2 mm/s). For the characterization of the surface quality, two orthogonal directions were considered: the longitudinal one, along the rolling direction, and the corresponding transversal one. Given the fractal nature of the surface, an investigation was done in order to assess its influence on the coefficient of abrasive friction. The fractal dimension Df, one of the most important parameters in a fractal surface analysis, was used to determine this influence in the global friction and abrasion phenomena. The abrasion factor was calculated using the Zum Gahr method for the data obtained with a specialized Mitutoyo SJ-301 surface tester. Measurements were made at the beginning, middle and at the end of the scratch channel. The obtained value for the abrasion factor was slightly less than zero. Other influences of anisotropic material features on global abrasion effects were also analyzed via comparisons of the coefficients of abrasive friction for both static and kinematic conditions.

Multi-cycle rolled aluminum alloy 3103 sandwiches: mechanical properties and stamp ability

Constructional part producing by sheet stamping of multilayer composites requires the stamping ability data. The aim of a work is to estimate mechanical properties, stamping ratio and anisotropy indexes of 2, 4, 8 and 12 layer sandwiches produced from aluminium alloy AA3103. The pieces were received by the cold rolling. Interoperation annealing was at 500°C for 1 hour. Charts of tensile strength, yield stress, elongation depending on layer thickness were composed. It was found that cold strain hardening does not disappear after annealing if the foil’s thickness become 0.4 mm and less. Microstructure analysis has shown a good contact between layers for all samples and thicker outer layers.

Study of Residual Stress Relaxation Mechanics Using a Micro-indent Method

The aim of this study is to show the feasibility and accuracy of a micro-indent method to comprehensively evaluate the relaxation mechanics of residual stress in specimens of rolled aluminium alloy. This micro-indent method was adapted to implement four annealing treatments. The residual displacements were measured using a high-accuracy measuring machine, which enables to decrease the absolute error down to ±300 nm. This study presents an innovative data analysis using Mohr's circles, which allowed to study all directions of the in- plane residual stress for different relaxation times. The results revealed that the relaxation process finishes when the residual stress relief is completed in some preferential directions and then, a brief stress recovery phase begins.

Salt fog corrosion behavior of friction stir welded AA2014-T651 aluminum alloy

AbstractHigh strength aluminum alloys of type AA2014 are used in aerospace applications. This alloy is considered unweldable using fusion welding processes. Friction stir welding being a solid state process has been proved to be a suitable process for obtaining sound welds of these materials. In the current study, 8 mm thick rolled AA2014-T651 aluminum alloy plates were joined using friction stir welding. The corrosion behavior of base material and friction stir welds was investigated using the salt fog test (ASTM B117). The corrosion resistance of the welds and parent material in the basic solution was found to be better than that in acidic and neutral solutions. It was also found that the corrosion rate increases with increase in time of exposure. It has been observed that corrosion attack is greater in the weld region than in the parent material and within the weld, heat affected zone has been found to be more susceptible to corrosion compared to the weld nugget and thermomechanically affected zone regions. Transmission electron microscopy studies revealed coarser precipitates and precipitate-free zones in the heat affected zone which are concluded to be the reasons for more susceptibility to corrosion.

Finite Element Simulation of Heat Transfer during Cryogenic Asymmetric Sheet Rolling of Aluminum Alloys

Aluminum and its alloys are widely used as structural materials in aerospace, automotive and other industries due to low density and high specific strength. Efficient way to increase strength and other properties of aluminum alloys is to form an ultra fine grain structure using severe plastic deformation methods. Cryogenic asymmetric sheet rolling under liquid nitrogen temperature is a process of severe plastic deformation that can be used to improve the aluminum alloys structure and properties. Prediction of sheet temperature during plastic deformation is very important. The temperature of sheet is changed due to the conversion of mechanical work of deformation into heat through sliding on contact surfaces. This paper presents the results of the finite element simulation of heat transfer during cryogenic asymmetric sheet rolling of aluminum alloy 6061. The effect of thickness reduction, rolling velocity and friction coefficient on the deformation heating and temperature field of aluminum alloy 6061 was found. The results of investigation could be useful for the development of the optimal treatment process of aluminum alloys by cryogenic severe plastic deformation to obtain the ultra fine grain structure and high strength properties.

Finite Element Simulation of Shear Strain during High-Ratio Differential Speed Rolling of Aluminum Alloy 5083

High-ratio differential speed rolling (HRDSR) is a process of severe plastic deformation (SPD) that can be used to improve the structure and properties of aluminum alloys. The mechanism of SPD during HRDSR comes from its large equivalent strain, which is composed of compressive strain and additional shear strain. Plastic strain control of aluminum alloys are of importance for improvement of sheet microstructure and properties. This paper presents the results of the finite element simulation of shear strain during high-ratio differential speed rolling of aluminum alloy 5083. Four deformation routes UD, TD, RD and ND were simulated. By the route UD the sheet was not rotated between two deformation steps, while by the other three cases it was rotated with 180° degrees. By the route RD the rotation axis was the rolling direction, by the route TD the transverse direction and by the route ND the normal direction. The effect of rolls velocity ratio, friction coefficient and deformation route on the shear strain and the effective strain of Al 5083 was found. The results of investigation can be used to optimize the high-ratio differential speed rolling process to improve microstructure and mechanical properties of aluminum sheets.

Modeling of Structure Evolution During Hot Rolling of Aluminum Alloys in the Software Package Deform

The study provides modeling of aluminum alloy 5182 БТ (Al-Mg 4,5%) structure evolvement during hot rolling in each stand of 5-stand continuous hot rolling mill. Mathematical modeling was made in DEFORM software product, Johnson-Mehl-Avrami-Kolmogorov equation was used for recrystallization kinetics setup. DEFORM enables to consider recrystallization of three types: dynamic, meta-dynamic and static recrystallization. Proceeding from actual rolling process temperature and speed parameters, the task was converted to static recrystallization calculation. Input coefficients were taken from literature data review. The output is volume of recrystallized grains and their sizes calculated throughout the rolling process. Description of processes related to grain size changes in rolling aluminum alloys is peculiar due to lack of consistent patterns. This is explained by the fact that grain growth during rolling is influenced by many factors associated with both internal metal structure and individual process specifics. That is why modeling results should be compared with industrial experimental data. In this case, texture and structure evolvement data received as a result of Hot Rolling Mill 2800 forced stop with subsequent quenching of metal were used for comparison.

Analysis of snake rolling force and torque with changes of thickness depending on unequal roll radii based on pure aluminum experiments

An analytical model, in which unequal radii are replaced with an equivalent radius, is creatively proposed to predict the rolling force and roll torque in general case of snake rolling. With the model, the effects of roll radius ratio, roll speed ratio, offset distance between rolls, reduction and friction coefficient on rolling forces in hot snake rolling of aluminum alloy are obtained. Also, the thicknesses of slab are investigated in different zones, which firstly propose the changes of thickness during snake rolling. Owing to the good agreement with the results measured in experiments and calculated by finite element method and other traditional models, those calculated by the proposed model are verified. The proposed model can be used to predict more accurate theoretical results for snake rolling force and torque.

The influence of work roll roughness on the surface/near-surface microstructure evolution of hot rolled aluminum–magnesium alloys

The effect of work roll roughness on the surface/near-surface evolution of aluminum alloys during hot rolling was examined with the use of a rolling tribo-simulator. Work rolls made of steel alloy AISI 52100 with two different surface roughness (Ra) values, 0.1μm and 1.1μm, were used to hot roll Al-Mg alloy samples under similar laboratory conditions for one and ten passes. Surface features on both rolled samples included cracks, grooves, and rolling ridges, but shingles were only observed on the samples rolled with the rougher work roll. Near-surface damage was observed to increase with work roll roughness. Cross-sectional examinations revealed that transverse micro-cracks on the sample rolled with the smoother work roll extended to depths of2.8μm, while cracks were 3.2μm in depth for the rougher work roll. In addition, the oxide-rich near-surface layers formed on the samples were thicker and more discontinuous for the rougher work roll. The oxide distribution in the transverse direction could be correlated to the size of the rolling ridges, which were larger for the samples rolled with the rougher work roll. A critical work roll surface roughness was proposed to influence the initiation of shingles on the aluminum alloy surfaces. The extent of the near-surface damage and the surface features formed on the rolled aluminum alloys were shown to be dependent on, but not limited to, the work roll surface topography.

Amorphous iron nanoparticles formed on aluminum surfaces during thermomechanical treatment

Iron nanoparticles were observed on the surface of commercial purity aluminum alloys after thermomechanical treatment using a hot rolling tribo-simulator with a roll surface roughness (Ra) of 0.01µm. These nanoparticles were spherical in shape and possessed an amorphous structure. They were observed lying on the oxide layer of the alloy surface and on crack faces. Iron nanoparticles have not been previously reported on aluminum surfaces under this thermomechanical condition. The surface of the hot rolled aluminum alloy was also covered with fractured iron-rich intermetallic particles embedded into the surface and caught within cracks.