Rolled Aluminum Alloy Research Articles

Microstructural Evolution of AA6082 with Small Aluminides under Hot Torsion and Friction Stir Processing

The hot rolled AA6082 aluminium alloy with aluminide dispersoids is deformed up to large strains to obtain a fine grained microstructure. Friction stir spot welding (FSSW) is carried out on rolled plates by means of a device provided by MTS System Corporation. FEM simulations determine that the material can flow up to local strains between 10 and 50 when the material reaches temperatures between 300-500°C. With this information, hot torsion tests at constant temperatures are carried out in a Gleeble ® 3800 machine for different strain rates. In both cases, in situ water quenching is applied to freeze the microstructure and avoid any static recrystallization effect after hot deformation. Light optical microscopy is used to identify the evolution of the grains as a function of the local deformation parameters determined by FEM simulations. The microstructure development by FSSW as well as by torsion is then further characterized by means of EBSD. At small strains the material deforms mainly by dynamic recovery with small low angle grain boundary formation and boundary dragging by fine aluminides and Mg2Si. At large strains grain refinement by continuous dynamic recrystallization takes place heterogeneously as a function of the original crystallographic orientation and precipitation state of each grain.

Effect of processing parameters on the relative density of spray rolling 7050 aluminum alloy strip

Spray rolling is a novel metallic semisolid near-net-shape forming technology. The problem of controlling the density of spray rolling aluminum strips is taken into two considerations: eliminating porosity before rolling and providing enough thickness reduction ratios during rolling. This simulation study reveals the relationship among the processing parameters of spray rolling, average solid fraction, and the relative density of a strip. The calculated values agree well with the experimental data. The densification mechanism during spray rolling process corresponds to the removal of porosity dominant regime. The relative density of spray rolling aluminum alloy strip depends heavily on both the solid fraction and thickness reduction ratios. The solid fraction in the range of 65–70 % corresponds with a good spray deposition condition and a high density level of strips. The present theoretical and experimental analyses suggest that spray rolling can be optimized to manufacture directly strips with a high density and excellent mechanical properties from liquid metal within one step.

Tribological Characteristics of Ai-Si Alloy Coating by Supersonic Particles Deposition

In order to improve the surfaced mechanical property of 7A52 aluminum alloy, Ai-Si alloy coating was prepared by Supersonic Particles Deposition (SPD) processing on the surface of 7A52 aluminum alloy. The wear-resisting property and wear mechanism of the coating were researched. The results show that the hardness of coating which reached to 266 HV, is similar with that of rolled 7A52 aluminum alloy; the wear weight loss of Ai- Si alloy coating decreased 40%, compared to that of 7A52 aluminum alloy on experimental condition. The dominant wear mechanism of Ai-Si alloy coating is abrasive wear, while the wear mechanism of 7A52 aluminum alloy is micro-cutting together with oxidation-wear.

DETERMINATION OF MATERIAL PARAMETERS OF SHEET METALS USING THE HYDRAULIC BULGE TEST

Hydraulic bulging experiments are performed in order to evaluate the mechanical parameters ofcold rolled steel (DC04) and aluminium alloy (EN AW 6016-T4) sheet materials. The biaxialyield stresses, and the biaxial anisotropy coefficients are derived from the biaxial stress-straincurves and the ratio between the strains in the transverse and in the rolling direction,respectively. The mechanical parameters resulted from the bulge test in combination with theresults from the tensile tests are used to determine the yield loci of the two materials. The effectof the number of input parameters on the capability of the BBC 2008 yield criterion to predictthe yield locus is also discussed in the paper.

Linking Porosity to Rolling Reduction and Fatigue Lifetime of Hot Rolled AA7xxx Alloys by 3D X‐Ray Computed Tomography

AbstractA set of hot rolled 7xxx aluminum alloys with different casting conditions and modification of processing conditions were analyzed on their fatigue life time as well as the internal microstructure using 3D computed X‐ray tomography with a lab scale scanner and optical microscopy. It is shown that large retained casting pores exist in samples with low reduction rate. The modification on the hot rolling process is now proved to be much more effective on removing large casting pores in the alloy. It is also found that with the improved casting conditions and the additional deformation imposed by increased rolling reduction, this advantage is getting retarded. The combination of porosity analysis with low cycle fatigue test at peak stress of 300 MPa indicates that reduction of the size of large pores in the sample down to 10 µm will lead to greatly improved fatigue life times.

Measuring and Modelling the Microstructures of Two-Phase Aluminium Alloys after Deformation

The effect of second-phase particles on the deformation and annealing behaviour of metals is re-assessed in the light of some new techniques. Using an EBSD method which provides much improved angular resolution, the effect of small non-deformable particles on the homogeneity of the deformation microstructure has been quantified. The presence of micron sized second-phase particles alters the deformation microstructure adjacent to particles, and a 3-d investigation of the deformation structures associated with large (>1μm) second-phase particles in cold rolled aluminium alloys has been carried out using 3-d FIB sectioning combined with EBSD, and the microstructures compared with the predictions of 3-d CPFEM modelling. The effects of grain orientation, strain and particle size have been investigated, and the results compared with earlier TEM investigations of such microstructures.

Plane strain compression of aluminium alloy sheets

The theory of plane strain compression is applied to rolled aluminium alloy sheet. Two contrasting grades of the alloy are tested: naturally aged AC 120 and half-hard HE 30. While AC 120 displays a smooth stress–strain curve under homogenous straining, HE30 shows a serrated stress–strain curve due to its banded plastic strain behaviour. It is shown that, provided the r-values can be established reliably to characterise each sheet’s orthotropy, a flow curve to large strain (≃2) is provided by the plane strain test. Certain modifications to the original test procedure are made to achieve this. Equivalence in flow curves, as required of orthotropic plasticity theory, is examined from plane strain, bulge forming and tension tests conducted at various orientations to the roll. Despite the contrasting limiting strains between the three tests (tension≃0.1, bulge forming≃0.8) an acceptable correlation has been found between their equivalent flow curves across three decades of strain. The dependence of equivalent plastic strain upon equivalent stress for each material conforms to the Hollomon law. The Ramberg–Osgood law allows for the addition of elastic strain.

Analysis of Edge Cracks in Hot Rolled Aluminium Alloy Sheets Contained of Magnesium for Can Usage

the edge crack frequently occurs in hot rolled 5182 alloy. SEM, EDS,etc.are used to analyze the factors leading to the cracks. It is discovered that high sodium content, and coarse intermetallic phase and inclusion are the main reason for these cracks. Meanwhile, some measures are suggested to be taken to avoid this kind cracks: making sure sodium content below 3 ppm; controlling the casting process and chemical composition to avoid coarse intermetallic phase; refining the melting aluminium to eliminate inclusion; setting a suitable scalping depth.

Relating the fatigue lifetime of hot rolled AA7xxx alloys to the pore size distribution as determined by 3D X-ray tomography

ABSTRACTA set of hot rolled 7xxx aluminum alloys with modification of processing conditions were analyzed on their fatigue life time as well as the internal microstructure using 3D computed X-ray tomography with a lab scale scanner and optical microscopy. It is shown that for conventional hot rolling conditions many large (>300μm) casting pores were retained in the material. With modifications of the rolling conditions the size and density distribution of the retained casting pores were significantly reduced, leading to greatly improved fatigue life times.

Quantifying microstructurally small fatigue crack growth in an aluminum alloy using a silicon-rubber replica method

A variation of the replica method is presented for quantifying microstructurally small fatigue crack growth rates in a rolled aluminum alloy. Repliset®, a two-part silicon-rubber compound, was employed to make surface impressions on notched specimens subjected to interrupted cyclic loading. Employing the high resolution capability of the scanning electron microscope, this replication method characterized fatigue crack growth rates of the 7075-T651 aluminum alloy for cracks as small as 10 μm in length.

Experiment on Hot Rolling Deformation Resistance of Aluminum Alloy and Mathematical Modeling

In order to investigate the impact factor of hot rolled aluminum alloy, a experiment was finished in a factory, to determine the effects of hot-rolled aluminum alloy plate with the system deformation resistance coefficient of the various factors and to mark the influence about the temperature to the hot rolling deformation resistance; Then, established the mathematical models of 1100,3003,5052 series hot rolled aluminum alloy plate's deformation resistance; The data calculated by the theoretical mathematical models is in good agreement the measured data. So this mathematical have the importance actual significance to actual production.

Aluminum Ingot Thermal Stress Development Modeling of the Wagstaff<sup>®</sup> EpsilonTM Rolling Ingot DC Casting System during the Start-up Phase

Based on sequentially coupled CFD and FEM models, aluminum alloy rolling ingot thermal stress simulations have been conducted in order to understand start-up phase cold cracking phenomena and optimize tooling designs for 520×2120 mm rolling ingot casting on Wagstaff® Epsilon™ Ingot Tooling. In the CFD model, ingot surface temperature dependant and water flow rate dependant water boiling curves are applied. Thermal boundary conditions for the complex water intrusion phenomena under the ingot butt have been attempted. Temperature dependant elastic-plastic materials constitutive relationship has been employed in the transient thermal stress FEM model. Results of thermal stress development at ingot surface and inside the ingot are presented; Connection of cold cracking (ingot butt quarter and center cracks) with near surface stress development at the ingot butt is shown and the effect of water intrusion under the ingot butt on the butt stress development is also discussed. The predicted temperatures are validated against temperatures measured from cast-in thermocouples at strategic locations in field ingots in order to obtain realistic thermal boundary conditions. The predicted butt curl is also verified through field observation and measurement.

Texture‐Induced Anisotropy in Asymmetrically Rolled Aluminium Alloys

AbstractThe formability of Al alloys is strongly correlated to the crystallographic texture and thus can be controlled by thermomechanical processing parameters. Texture‐induced anisotropy is studied in asymmetrically hot and cold rolled Al alloys from the 6xxx series. It is found that the strain mode of both hot and cold rolling processes significantly affects the anisotropy of recrystallized material. The recrystallization textures produced in the ASR process improve the normal anisotropy, whereas the in‐plane anisotropy does not benefit significantly from the ASR process. Results of crystal plasticity calculations show that an improved normal anisotropy in asymmetrically rolled sheets (${\bar {r}}$ = 0.77) ensures an increased limiting drawing ratio of ≈ 2.11, which is beneficial for formability.

Comparative study on effects of microstructures of hot rolled and twin roll casting 1235 aluminium alloy on surface quality of aluminium foils produced

Twin roll casting is an attractive technology for producing aluminium sheets for foils. But, surface defects, such as matte defects, may occur on aluminium foils produced in this way. However, it is not the case on aluminium foils produced by traditional hot rolled process. Optical microscopy, scanning electronic microscopy, energy spectrum and transmission electronic microscopy were used to investigate the effects of the microstructures of the twin roll cast and hot rolled aluminium alloy sheet for foils on the surface defects of the foils produced. It is discovered that central segregation band and surface microsegregation band in twin roll casting aluminium sheet may result in a non-uniformly distributed secondary Al–Fe and Al–Fe–Si particles in workpieces in a lower reduction pass. These non-uniformly distributed Al–Fe and Al–Fe–Si particles and microporosities in a size of several microns generated in solidification process of twin roll casting are the main cause for the surface matte defects of the aluminium foils produced.

Modeling and simulation of constituent particle clustering and distribution in rolled aluminum alloys

It is recognized that corrosion damage in aluminum alloys is the direct result of local galvanic coupling between constituent particles and the metal matrix. Heavily clustered groups of constituent particles have been shown to form the most severe corrosion pits, and the morphology of these pits has been found to exhibit a strong correlation with that of the instigating particle cluster. To predict damage evolution accurately in three dimensions, the spatial distribution of the constituent particles in a given material must be quantified. The tomographic reconstruction methods currently available are time consuming and possess characteristic length scales that are insufficient for large-scale corrosion studies. To accommodate this larger length scale, a model for three-dimensional constituent particle microstructure is proposed. This model employs a fusion of classic stereological techniques and qualitative observations to describe the constituent particle microstructure of rolled aluminum alloys in three dimensions. A method is described for generating statistically representative three-dimensional constituent particle microstructure from two-dimensional orthogonal cross sections. This novel simulation algorithm allows for detailed three-dimensional particle microstructure simulations to be carried out using standard optical microscopy and image analysis techniques.

Effects of rolling parameters on temperature distribution in the hot rolling of aluminum strips

A model for the study of hot strip rolling of aluminum alloys is proposed, and the approach is based on thermo-mechanical analysis using the Finite-Element Method (FEM). To assess the rolling behavior of materials during a pass, finite element program Abaqus/Explicit has been employed and the hot rolling process was modeled in three dimensions. The appropriate models for heat transfer mechanisms are considered and the temperature distribution along the rolled strip and the temperature variation during hot strip rolling process is predicted. The effects of various process parameters such as rolling speed, amount of thickness reduction, initial thickness of the strip and interface heat transfer coefficient are considered. To verify the validity of the model and predicted results, a multi-pass hot rolling program is used and a comparison is carried out between the predicted results by model with plant-recorded results.

Near-Surface Deformed Layers on Rolled Aluminum Alloys

Near-surface deformed layers, which are characterized by nano-sized fine grains, are generated in aluminum alloys by hot and cold rolling. During the rolling processes, the alloy surface and near-surface regions experience a high level of shear deformation that results in significant microstructure refinement, leading to formation of near-surface deformed layers with microstructures different from that of the underlying bulk alloy. Two types of near-surface deformed layers are observed. Type A is characterized by fine grains with grain boundaries decorated by oxide particles; type B is characterized also by fine grains but with the grain boundaries free of oxide particles. The high levels of shear deformation result in dynamic recrystallization. Together with mechanical alloying, this is responsible for the formation of the near-surface deformed layer. Furthermore, the structure in the near-surface deformed layer can survive the typical annealing process particularly if the grain boundaries are pinned by oxide particles.

Formation of a single, rotated-Brass {1 1 0}〈5 5 6〉 texture by hot cross-rolling of an Al–Zn–Mg–Cu–Zr alloy

The present work describes the evolution of a strong, single-component rotated-Brass ((1 1 0) ) texture in an Al-Zn-Mg-Cu-Zr alloy by an uneven hot cross-rolling with frequent interpass annealing. This texture development is unique because hot rolling of aluminum alloys results in orientation distribution along the ``beta-fibre''. It has been demonstrated that the deformation by cross-rolling of a partially recrystallized grain structure having rotated-Cube and Goss orientations, and the recrystallization resistance of near-Brass-oriented elongated grains play a critical role in development of this texture. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Effect of stress on the annealing behavior of severely plastically deformed aluminum alloy 3103

The influence of a mechanical stress during annealing on the softening behavior of an ECAP deformed and a cold rolled aluminum alloy 3103 was investigated. An analysis of the work hardening behavior and the microstructural evolution during annealing proved that recrystallization is substantially retarded by the applied stress. This can be attributed to significantly accelerated recovery processes.

Effects of laser peening treatment without protective coating on axial fatigue property of aluminum alloy

Axial fatigue tests with stress ratio of −1 and 0.1 were conducted in order to investigate effects of laser peening treatment without protective coating (LPwC) on fatigue property such as the fatigue strength and the surface crack behaviors of rolled aluminum alloy A7050-T7451 for aircraft structures. As results, The LPwC treatment was effective for the fatigue strength improvement in fatigue lives regime before 2∼3×106 cycles, but the treatment reduced the strength after the cycles at the both stress ratios conditions. Fatigue cracks initiated at the surface on the higher stress amplitude levels, but the cracks initiated in the internal positions on the lower stress levels. From these results, it is clear that the LPwC treatment could control the crack initiation and propagation behaviors. The fatigue crack propagation property from the pre-crack by the LPwC treatment was evaluated by the stress intensity factor range including the residual stress induced by the LPwC treatment.