Commercial Purity Aluminium Alloy Research Articles

Failure mechanism during incremental sheet forming of a commercial purity aluminum alloy

Incremental sheet forming (ISF) is known for many advantages over conventional forming, such as part flexibility, low tooling cost and higher formability. Previously various studies have explored the failure mechanism experimentally and numerically. However, limited studies have been performed on the micro-mechanics of failure during ISF process. This study involves failure mechanism during incremental sheet forming of a commercial purity aluminum alloy (AA1050). During experiments, failure (fracture) was observed in truncated cone specimens by increasing the wall angle from 71° to 72°. The mechanism behind failure was explored with detailed microstructural characterization and finite element (FE) simulations. Various samples were taken from the successfully formed and failed cones for microstructural analysis. The electron backscatter diffraction (EBSD) based microtexture measurements associate this failure with more grain fragmentation and necking or localized deformation in the failed cone. Further, the X-ray diffraction (XRD) based residual stress measurements indicate high positive (tensile) hydrostatic stresses (∼157 MPa) on the outer surface of the failed (fractured) cones. Finite element analysis (FEA) with Gurson-Tvergaard-Needleman (GTN) damage model was used for fracture prediction. The FEA results also support the residual hydrostatic stress evolution in the cones, albeit at a slightly different wall angle. Based on microstructural and finite element analysis it is concluded that deformation becomes inhomogeneous when the failure occurs during ISF process.

A Correlation between Deformation-Induced Surface Roughness and In-Plane Plastic Strain in an Aluminum Alloy at the Mesoscale

Experimental and numerical studies on deformation-induced surface roughening in a commercial purity aluminum alloy are presented and discussed. Mesoscale surface profiles evolving in the experimental and numerical specimens in the course of tension are processed to reveal a correlation between roughness characteristics and in-plane plastic strains at the mesoscale. A dimensionless parameter calculated as a ratio of the rough profile length to the profile evaluation length has been used for quantitative estimations of the mesoscale roughness patterns. The dimensionless roughness parameter is shown to depend exponentially on the in-plane plastic strains at the mesoscale. The results support an early assumption that in-plane plastic strains accumulated in a loaded material can be evaluated from the estimations of mesoscale surface roughness.

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.

The effect of iron and the precipitation behavior of iron during annealing of a cold deformed commercial purity aluminium alloy

Iron is always present in any aluminium alloy and usually as an impurity element. In commercial purity alloys the concentration of iron is typically so large that iron has a strong influence on the material properties, due to its slow diffusivity and low solubility in aluminium. In the present work the effect of iron in solid solution and the precipitation behavior of iron during annealing of a cold-deformed commercial purity aluminium alloy have been investigated. Iron in solution is found to have a strong retarding effect on the softening kinetics. The resulting recrystallization texture has a distinct Cube component and some weak deformation texture components. By additional cold rolling and inter-annealing, the solute content is reduced significantly by precipitation of mainly Al3Fe and some α-AlFeSi phases. Doing so speeds up the softening kinetics by a factor of ~1000 and causes a considerable strengthening of the Cube component in the recrystallized texture.

A direct comparison of high temperature nanoindentation creep and uniaxial creep measurements for commercial purity aluminum

Measuring the uniaxial creep response from nanoindentation has been of great interest to the small scale mechanics community. However, several experimental and modeling challenges pose obstacles to direct comparison of indentation and uniaxial results. In this work, new experimental procedures are developed to improve the precision and accuracy of high temperature nanoindentation tests. Indentation creep experiments are performed on commercial purity aluminum alloy at a number of temperatures up to 550 °C. The activation energy for creep was found to be 140.2KJ/mol/K, matching the value determined with high temperature uniaxial creep experiments extremely well. Uniaxial power-law creep parameters (stress exponent and pre-exponential term) are calculated from the indentation data for direct comparison of results to the uniaxial data. The results are in good agreement with the literature values for uniaxial compression/torsion tests over a wide range of strain rates and temperatures demonstrating the capabilities of high temperature indentation creep experiments. The relative contributions and interplay of indentation size effect, strain rate and temperature on the creep response is also explored.

Modeling of isothermal recovery and recrystallization kinetics by means of hardness measurements

Recovery and recrystallization, which may happen during annealing of materials, are very important technological processes through which many properties of the material can be changed. Hence, reliable and efficient modeling of the softening process is vital. Hardness can be used as a simple and cheap measure to model the softening processes. In the present study, the isothermal recovery and recrystallization kinetics of a commercial purity aluminum alloy AA1050 is experimentally modeled using hardness test at four temperatures from 285 °C to 400 °C after cold rolling to various reductions. In order to achieve more accurate analysis, hardness data points are increased and a statistical method is used. The isothermal recovery and recrystallization kinetics are described by a logarithmic and the Johnson‐Mehl‐Avrami‐Kolmagorov relationships, respectively. It is found that hardness measurements can be performed as a parameter to quantify recovery and recrystallization kinetics. The constants of models and the activation energies for both processes are calculated in the different conditions. These constant parameters are dependent to the temperature. Also, the activation energies of recovery and recrystallization rise as these transformations proceed.

AA1070 알루미늄 합금의 사각형상 충격압출 성형에 미치는 공정 조건의 영향

Impact extrusion is an economical and productive process that can replace the multistage deep drawing process for producing deep rectangular cases. In the current work, a three-dimensional finite element analysis of the impact extrusion process of a commercial purity aluminum alloy (AA1070) was performed to predict loads, material flow, and deformed shapes using the Hansel-Spittel rheology law, which describes the flow stress at various temperatures and strain rates. The role of various process parameters such as friction, clearance between punch and die, aspect ratio and thickness of billet on the process and the shapes was analyzed.

Structure Development and Deformation Behaviour of Pure Aluminium Processed by Constrained Groove Pressing

In this study, the relationship between the structure and properties of commercial purity aluminium alloy A1199 was investigated by applying constrained groove pressing (CGP) deformation method. The refinement of the coarse grain aluminium (Al) microstructure to sub microcrystalline size by large plastic strain at room temperature defined. The impact of various strains upon microstructure changes is investigated using transmission electron microscopy (TEM of thin foils) and electron back scatter diffraction (EBSD). A mixture of subgrains produced by grains subdivision and polygonized subgrains formed locally due to dynamic recovery was found in the deformed aluminium structure. The tensile properties and resulting hardness are related to microstructural evolution induced by constrained groove pressing deformation. A substantial impact of straining upon the increasing in tensile strength was observed after the first deformation step (first pass) Further strain increase had an insignificant effect on tensile strength but was accompanied by ductility loss. The post deformation annealing effect was then explored with aim to increase the ductility. The results indicate that changes in strength and ductility may be related to formation of a bimodal structure in deformed plates.

Recrystallization Microstructure and Texture of Highly Strained Commercial Purity Aluminium Alloy

The microstructural and textural evolutions during annealing of a highly strained (ε=4.0) commercial purity aluminium (AA1200) were followed by electron backscatter diffraction (EBSD). Boundary spacings were analyzed for crystallites of different crystallographic orientations. It was found that initially during the annealing the microstructural evolution is dominated by recovery of the highly strained microstructure, while later the microstructure consists of identifiable grains nucleating and growing at the expense of deformed and recovered matrix. No much texture change occursduring early stages of annealing, whereas a cube texture evolves and dominates after complete recrystallization.

3D microband boundary alignments and transitions in a cold rolled commercial purity aluminum alloy

Abstract In the study of microband formation during plastic deformation of face centered cubic metals and alloys, two theories have been proposed regarding the orientations of their boundaries: (i) they are aligned parallel to crystallographic planes associated with dislocation glide (i.e. {111} planes in FCC metals), or (ii) they are aligned in accordance with the macroscopic stress state generated during deformation. In this study, high resolution 3D electron backscatter diffraction (3D EBSD) was used to investigate the morphology and crystallographic nature of microband boundaries within a 19 × 9 × 8.6 μm volume of a deformed grain in commercial purity aluminum cold rolled to 22% reduction. It was found that microband boundaries correspond to both theories of orientation. Additionally, a single surface may contain both crystallographic and non-crystallographic alignments. Misorientations across boundaries in the regions of microband triple junctions have been identified for both boundary alignments.

Microstructural path model and strain dependence of recrystallisation in commercial aluminium

The isothermal recrystallisation of commercial purity aluminium alloy AA1200 cold deformed to either a true strain of 2 (86·5% reduction in thickness) or 4 (98·2% reduction in thickness) was studied phenomenologically in each material by means of quantitative microscopy. The microstructural path descriptors, VV, the volume fraction recrystallised, and SV, the interfacial area density separating recrystallised grains from deformed grains were measured stereologically by electron backscatter diffraction and microstructural path model parameters were deduced for each strain. The effects of strain were delineated and compared with the results of recrystallisation in a slightly different commercial aluminium alloy AA1050 deformed to a true strain of 2·3.

Influence of rolling direction on strength and ductility of aluminium and aluminium alloys produced by accumulative roll bonding

Sheets from commercial purity aluminium AA1050 and aluminium alloy AA6016 were processed by accumulative roll bonding to obtain an ultrafine-grained microstructure. The accumulative roll bonded samples showed a significant increase in specific strength paired with high ductility. Despite a strongly elongated grain structure, tensile testing of samples oriented 45° to the rolling direction revealed considerable improvement in elongation to failure compared to the samples oriented parallel to the rolling direction. From hydraulic bulge tests, it was observed that the accumulative roll bonded samples reached higher burst pressures and slightly lower equivalent strains in comparison to the as-received conventionally grain-sized samples. This behaviour reflects the extraordinary mechanical properties of the ultrafine-grained materials and indicates promising metal sheet formability.

Deformation Behaviour of Accumulative Roll Bonded and Friction Stir Welded Aluminium Alloys

Commercial purity aluminium AA1050 and aluminium alloy AA6016 were accumulative roll bonded and subsequently friction stir welded. The microstructure of the conventional and ultrafine-grained materials produced by accumulative roll bonding is strongly affected by friction stir welding. The elongated ultrafine-grained microstructure of roll bonded sheets becomes coarser and equiaxed in the nugget region. Hydraulic bulge tests showed that higher burst pressure can be achieved for samples without friction stir welding than for the ones with friction stir welding. Localised deformation, crack initiation and propagation, as well as the final fracture occurred within the nugget. Friction stir welded AA1050 sheet showed similar achievable burst pressures and von Mises equivalent strains compared to the as-received conventionally grained sheets. On the other hand, significantly higher burst pressures and at the same time higher von Mises equivalent strains were observed for the friction stir welded ultrafine-grained material than for the friction stir welded conventionally grained material.

Cube texture in hot-rolled aluminum alloy 1050 (AA1050)—nucleation and growth behavior

The microstructure and texture evolution at different annealing temperatures were analyzed in a hot-rolled commercial purity aluminum alloy from two-dimensional electron backscattered diffraction scans. The newly recrystallized grains were found to cluster together. Recrystallized grains have cube, { 0 0 1 } 〈 1 0 0 〉 , as the dominant texture component at all annealing temperatures. Nucleation and growth behavior of the recrystallized cube grains was observed by measuring the variations in first nearest neighbor boundary pixels of these grains. The texture of nearest neighbor pixels at low fraction recrystallized represents the nucleation environment of newly recrystallized grains. Growth rates of the recrystallized grains were estimated from the variation in grain size with time at different annealing temperatures. Analysis of nucleation and growth behavior of the recrystallized cube grains reveals a significant nucleation advantage at all annealing temperatures: a decreasing growth advantage is observed as the annealing temperature is increased. Further analysis of the nucleation environment of the recrystallizing cube grains also revealed that among the main texture components of deformed grains (S, brass and copper), they grow more rapidly into the S component than into the copper or brass components. This trend persists throughout recrystallization such that the brass component is the slowest to recrystallize. In terms of the oriented nucleation (ON) and oriented growth (OG) theories, ON has a greater impact on the development of recrystallization texture than OG.

An analysis of microband orientation in a commercial purity aluminium alloy subjected to forward and reverse torsion using Electron Backscatter Diffraction (EBSD)

High-resolution electron backscatter diffraction has been used to study the effects of strain reversal on the evolution of microbands in commercial purity aluminium alloy AA1200. Deformation was carried out using two equal steps of forward/forward or forward/reverse torsion at a temperature of 300 degrees C and strain rate of 1 s(-1) to a total equivalent tensile strain of 0.5. In both cases, microbands were found in the majority of grains examined with many having microband walls with more than one orientation. For the forward/forward condition, the microband clusters were centred around -20 degrees and +45 degrees to the equivalent tensile stress axis, whereas for material subjected to a strain reversal, the clusters were at -65 degrees and -45 degrees . There was no evidence of microbands that were formed in the forward deformation step in the reversed material, which would suggest that a strain of 0.25 is sufficient to dissolve any microstructure history generated by the first step. Furthermore, the microbands within the strain-reversed material had a reduction in misorientation compared with the lineally strained material, suggesting that these microbands only formed at the onset of the second deformation step. This confirms that microband formation is complex and sensitive to strain path; however, it is still unclear to what extent microband formation is dependent on strain path history compared with the instantaneous deformation mode.

Measurement of magnitude and direction of velocity in high-temperature liquid metals. Part II: Experimental measurements

Experimental research work on the application of the sphere melting technique to measure magnitude as well as direction of velocity in liquid metals is the focus of Part II of this series of articles. The sphere melting time is detected by means of a sensing wire, which is connected to a specially designed electrical circuit. A novel apparatus is used whereby liquid metal is rotated with a specified tangential velocity. To measure the magnitude of velocity, the sensing wire of the sphere melting is located at the center of the sphere. To detect the direction of flow, three sensing wires are employed. These wires are placed at strategic locations inside the sphere and detect the melting times at three different locations. The ratio of the melting times of these locations identifies the direction of the flow. The experimental results are compared against model predictions. In addition, an error analysis is carried out to discover the possible sources of error in the detection of metal velocity. The liquid metals used in this research work are commercial purity aluminum and AZ91 magnesium alloy.

The effect of quench paths on hardness in an infinitely long aluminium cylinder

A single-internal variable constitutive model is used to predict the micro-hardness for a commercial purity aluminium alloy subjected to various quenching histories. The delayed quenching, higher nucleate boiling amplitude, and wider nucleate boiling range increase the micro-hardness. A limited study of the effect of cylinder size does not yield significant changes in the microhardness. The modelling methodology developed here can be used in modelling commercial quenching processes.

Microstructural path and temperature dependence of recrystallization in commercial aluminum

The isothermal recrystallization of 90% cold-rolled commercial purity aluminum alloy AA1050 was studied by means of quantitative microscopy at four temperatures from 245°C to 280°C. The microstructural properties, V v, the volume fraction recrystallized, S v, the interfacial area density separating recrystallized grains from deformed grains and 〈 λ〉, the mean recrystallized grain free length, were measured stereologically as a function of time. The kinetics, microstructural path, grain boundary migration rates and temperature dependence of recrystallization were quantified experimentally. Based on analysis of all data and microstructural path modelling, recrystallization was determined to be growth (boundary migration rate) controlled; all nucleation occurred in time periods short compared to the earliest annealing times. The activation energy for grain boundary migration was calculated to be 172–183 kJ/mole suggesting that a solute-limited grain boundary migration rate mechanism was operative in the alloy. The recrystallization microstructural path was found to be isokinetic, i.e. identical at all the annealing temperatures studied. Two stages of recrystallization kinetics were observed; an early transient-like stage characterized by decreasing growth rates and a later stage in which the kinetics approached Avrami behavior and the growth rates were approximately constant. The transient-like behavior is attributed to the steep, deformation-induced stored energy gradients surrrounding precipitate particles where the recrystallized grains are nucleated.

Finding boundary conditions: A coupling strategy for the modeling of metal casting processes: Part I. Experimental study and correlation development

A generalized temperature boundary condition coupling strategy for the modeling of conventional casting processes was implemented via experiments and numerical simulations with commercial purity aluminum, aluminum alloy, and tin specimens in copper, graphite, and sand molds. This novel strategy related the heat transfer coefficient at the metal-mold interface to the following process variables: the size of the air gap that forms at the metal-mold interface, the roughness of the mold surface, the conductivity of the gas in the gap, and the thermophysical properties of both the metal and mold. The objective of this study was to obtain, apply, and evaluate the effect of incorporating an experimentally derived relationship for specifying transient heat transfer coefficients in a general conventional casting process. The results are presented in two parts. Part I details the implementation of a systematic experimental approach not limited to a specific process to determine the heat transfer coefficient and characterize the formation of the air gap at the metal-mold interface. The heat transfer mechanisms at the interface were identified, and seen to vary in magnitude during four distinct stages, as the air gap formed and grew. A semiempirical inverse equation was used to characterize the heat transfer coefficient-air gap relationship, across the various stages, for experimental data from the literature and this study.

Recrystallization texture in a cold rolled commercial purity aluminum: on the plausible macro- and micro-mechanisms

In the cold rolled commercial purity aluminum alloy AA1080, the most significant aspect of the recrystallization texture is the strengthening of the Cube {001}〈100〉 component. The increase is primarily attributed to the ‘frequency advantage’ of the Cube grains—i.e. the recrystallized Cube grains are higher in number but not larger in size. In general, Cube grains appear first and the deformed Cube regions have lower stored energies. The average spacing (along normal direction, ND) of the original hot band Cube regions is 450 μm, while average Cube band spacings after 60 and 80% deformations are 195 and 120 μm. Recrystallized Cube grains originate from these deformed Cube bands and an approximate estimation of the nucleation ability (the so-called nucleation factor of Cube or N C ) of the Cube bands is obtained from the geometrical relationship A C = N C d C / λ C , where A C , d C and λ C are the area fraction, average recrystallized Cube grain size and average spacing of the deformed Cube bands, respectively. Irrespective of annealing at 350 or 500°C, approximate N C values are estimated as 0.94 and 0.83 after 60 and 80% deformation. The apparent drop in N C after 80% deformation, in spite of the observation that more of deformed S {231}〈346〉 is found next to deformed Cube, belittles the possible role of ‘micro-growth advantage’ in determining the ‘final’ Cube recrystallization texture.