Pitches are used on a large scale in the manufacture of carbon anodes for the production of primary aluminium. The role of the pitch is to act as a binder between the petroleum coke grains. The structure of the carbonized pitch binder (pitch coke) has an important impact on the overall performance of the anode. Even though the binder pitch is the minor constituent in an anode, it is impossible to make a good quality anode without a good quality binder pitch. Pitch is an extremely complex mixture of numerous, essentially aromatic and heterocyclic compounds derived from pyrolysis of organic material or tar distillation. Upon heat treatment pitches form cokes in relatively high yields. Physical and chemical properties of the anode such as mechanical strength, electrical resistivity, thermal conductivity and resistance towards oxidation by air and CO2 are dependent on the structure of the aggregate material as well as the carbonized binder pitch. The properties of the pitch coke is in turn mainly dependent on the chemical characteristics of the parent pitch. Coal-tar pitch is the preferred choice of binder material in anode manufacture today. However, the availability of high quality coal-tar is in decline and at least partial replacement by alternative binder sources will become increasingly important in the future. Due to environmental regulations, petroleum pitches are interesting as they generally have lower PAH emissions than coal-tar pitches during baking. Blends of coal-tar pitches and petroleum pitches are in use today on an industrial scale. The aluminium industry must be prepared to meet the challenges involved in adapting binder pitches from new sources which may be of inferior quality to the pitches available on the market today. An increased understanding of the processes involved in the transformation of a pitch into a coke and the link between raw material composition and properties and the final artifact is thus highly relevant. Traditionally, the suitability of a binder pitch for use in anodes, has been defined from parameters like softening point, insolubility in toluene (TI) and quinoline (QI), coke yield, H/C atomic ratio, ash content and density. Although these parameters, which are mostly empirical in nature, give an indication of the pitch quality, more information on the chemical characteristics and carbonization behavior of pitches is certainly valuable. The present work aims to describe and explain the link between “classical” pitch properties, hydrogen transfer properties, information derived from NMR spectroscopy and the structure of the carbonized binder pitch. Coal-tar and petroleum pitches pass through a fluid stage during carbonization. In the early stages of carbonization, free radicals are formed due to thermal rupture of C-C and C-H bonds in reactive components. Polymerization occurs mainly via a free radical mechanism leading to molecular size enlargement (aromatic growth)and the formation of oligomeric systems (mesogens). If the intermolecular reactivity of the pitch constituents is too high, extensive cross-linking and a rapid transformation of pitch molecules through polymerization will occur at a relatively low temperature. In this case, either mesophase will not be formed or the growth and coalescence of mesophase will take place under low fluidity/high viscosity conditions leading to a premature solidification of the pyrolysis system. An isotropic coke or a pitch coke of small optical domains will then be formed. On the other hand, if the pitch has a low thermal reactivity, aromatic growth is constrained and the mesogens will have sufficient mobility to stack parallel to each other and establish a liquid crystal system (mesophase). The growth and coalescence of mesophase take place at a higher temperature where the viscosity of the pyrolysis system is at a low level. Eventually, the system will solidify and an anisotropic coke of large well-developed optical domains is formed. In particular, the presence of alkyl side chains and oxygenated functional groups are considered to lead to an increased thermal reactivity. If free radicals formed by thermal rupture of bonds in reactive pitch species can be stabilized by hydrogen transfer from within the system, extensive cross-linking at a too early stage is prevented. The initiation, growth and coalescence of mesophase are facilitated and consequently a coke of large well-developed optical domains is formed. Hydroaromatic rings and naphthenic rings in hydroaromatic species are considered to be principal hydrogen donor groups. Oxygen acceptor sites are believed to deplete the supply of donatable hydrogen and leave radicals free to recombine. The thermal reactivity of a pitch is thus dependent on both the amount of reactive species and the ability of the pitch to stabilize free radicals by hydrogen transfer. In the present work, the subject of study was five coal-tar pitches and four petroleum pitches. In addition, a QI-free coal-tar pitch supplied by GrafTech International was studied. The pitches were characterized by 1H NMR and 13C NMR spectroscopy, hydrogen transfer properties, elemental analysis and the release of volatiles during carbonization. In addition, the pitches were characterized by more “traditional” pitch parameters like insolubility in quinoline (QI), insolubility in toluene (TI), softening point and coking value. The structure of the carbonized pitches was examined by optical microscopy and X-ray diffraction. The hydrogen transfer properties of the pitches were evaluated from their ability to donate hydrogen to an acceptor compound, anthracene, or abstract hydrogen from a donor compound, 1,2,3,4-tetrahydronaphthalene (tetralin). A mixture of pitch and anthracene or tetralin was heat treated in sealed glass tubes filled with argon gas at 400 ºC. Two different heat treatment procedures were tested. In the first, the sample was kept at 400 ºC for 8 hours while in the second, the sample was heated at a rate of 5 ºC/min to 400 ºC with no soaking time. The major hydrogenated products from the reaction between anthracene and pitch were 9,10-dihydroanthracene (DHA) and 1,2,3,4-tetrahydroanthracene (THA). After the reaction, the semi-coke residue was dissolved in carbon disulphide and analyzed by gas chromatography. The hydrogen donor ability (HDa) was calculated from the amounts of DHA and THA formed and expressed as milligrams of hydrogen transferred to anthracene per gram of pitch. For the hydrogen donor ability test, the less severe heat treatment (5ºC/min to 400 ºC, no soaking time) was found to be the most appropriate. The reaction between tetralin and pitch gave one major dehydrogenated product, naphthalene. The hydrogen acceptor ability (HAa) was calculated from the ratio of naphthalene to tetralin as determined by gas chromatography and expressed as milligrams of hydrogen transferred per gram of pitch. For the acceptor ability test, the heat treatment at 400 ºC with 8 hours soaking time was found to be the most appropriate. The release of volatiles during carbonization was studied by thermogravimetric analysis. The amount of volatiles released between 300 and 500 ºC (VM300-500)relative to the total amount of volatiles released at 1000 ºC was selected as a parameter reflecting the thermal behavior of pitches during the critical stages of carbonization. Carbonization of pitches was performed under inert gas pressure (15 bar) and the green cokes obtained at 550 ºC were studied by optical microscopy. Computerized image analysis was performed to quantify the optical texture. The output parameters from the image analysis were the mosaic index, which is a measure of the optical domain size, and the fiber index, which is a measure of the parallel alignment of optical domains. The green cokes were further heat treated to 1150 ºC and the microstructure of the resulting calcined pitch cokes was characterized by X-ray diffraction. The carbon disulphide soluble part of the pitches was investigated by 1H NMR and 13C NMR spectroscopy. Results from elemental analysis of the pitches were used in conjunction with the results obtained from the NMR spectroscopy. The main objective of the NMR analysis was to identify and quantify structures in the pitch which are considered either to increase or decrease the thermal reactivity. The coal-tar pitches were as expected found to be more aromatic than the pitches of petroleum origin. A relationship was found between the aromaticity of the pitches and the H/C atomic ratio as determined from elemental analysis. Elemental analysis is a rapid and convenient method to estimate the aromaticity of pitches. Due to a more hydroaromatic structure, the petroleum pitches were in general found to have a higher estimated concentration of donatable hydrogen which will suppress intermolecular reactivity. However, the petroleum pitches also had a high concentration of alkyl side chains which are generally believed to give increased thermal reactivity. Carbon connected to oxygen could not be distinguished in the NMR spectra. Pitch constituents containing heteroatoms are generally concentrated in the heavier pitch fractions which may not be soluble in carbon disulphide. This could be an explanation for the failure in the detection of aromatic carbon connected to heteroatoms. However,the oxygen content was determined by elemental analysis. The pitches could be distinguished due to their ability to donate hydrogen to anthracene or abstract hydrogen from tetralin. The hydrogen donor ability was not found to correlate with the concentration of donatable hydrogen (NMR) which might have been expected. A likely explanation for this apparent inconsistency is that potential donatable hydrogen in reactive pitches will be preferentially consumed by free radicals and oxygenated acceptor sites instead of being transferred to anthracene. A correlation between the hydrogen donor (HDa) and acceptor ability (HAa) was not found. This indicates that the two parameters represent two separate properties where both are linked to the thermal reactivity of the pitch. The ratio between the hydrogen donor and acceptor ability, HDa/HAa, was used as a parameter reflecting the thermal reactivity of pitches. Pitches which exhibit a high HDa/HAa ratio (low thermal reactivity) are expected to form an anisotropic coke of large optical domains. On the other hand, pitches with a relatively low HDa/HAa ratio are expected to have a high thermal reactivity and form a more isotropic (small optical domains) coke. Despite the higher concentration of donatable hydrogen, the petroleum pitches were not generally considered to have a lower thermal reactivity than the coal-tar pitches expressed by the HDa/HAa ratio. The processes taking place during thermal treatment of pitches are reflected in the release of volatiles. A correlation was observed between the HDa/HAa ratio and the relative amount of volatiles released between 300 and 500 ºC (VM300-500). Thermally reactive pitches exhibiting a low HDa/HAa ratio will have a high activity at low temperatures and release low boiling point molecules and fragmentation species. If on the other hand the pitch has a low thermal reactivity, fragmentation species will be stabilized by hydrogen transfer and retained in the pyrolysis system. The resulting thermally stable molecules of relatively low molecular weight may then act as solvating vehicles maintaining a low viscosity in the system and may also be important as hydrogen shuttling agents. When the system has reached a critical stage for mesophase growth and coalescence, these smaller thermally stable molecules (non-mesogens) are eventually released at higher temperatures. The petroleum pitches developed cokes of relatively large optical domains (coarse mosaic). A correlation was observed between the HDa/HAa ratio and the mosaic index (size of optical texture) for the petroleum pitches. As expected, a high thermal reactivity (low HDa/HAa ratio) resulted in a pitch coke of small optical domains (high mosaic index). The HDa/HAa ratio was, however, not successful in predicting the size of optical texture in the cokes obtained from the coal-tar pitches. This was mainly due to the influence of QI material on the pitch coke structure. It is recognized that particulate matter (primary QI material) hinders the growth and coalescence of mesophase. This was found for the coal-tar pitches. Scanning electron (SEM) and polarized light microscopy images taken at a high magnification revealed how the QI particles were arranged and clustered around smaller anisotropic domains. The detrimental effect of QI material on the development of anisotropic texture in the resulting coke was demonstrated by comparing the structure of the coke obtained from a QI-free coal-tar pitch and a coal-tar pitch containing QI. The QI-free pitch developed a coke of large optical domains whereas the coke obtained from the pitch containing QI material had mainly a fine mosaic texture (small optical domains). However, some large anisotropic domains were present in between the QI clusters. It is also not to be excluded that the QI fraction not only acts physically by obstructing the growth and coalescence of mesophase but may also be chemically active. Findings indicate that the oxygen is concentrated in the QI fraction. Solid QI particles with oxygenated functional groups or heteroatomic structures containing oxygen, which due to their large size are insoluble in quinoline, may act as acceptor sites for hydrogen thus increasing the thermal reactivity. The average coherent stacks of the calcined (1150 ºC) pitch cokes was found to consist of between 7 and 8 graphene layers (Lc divided by d002). The average crystallite size (Lc) was fairly similar for all the calcined pitch cokes but significant differences were found. The coal-tar pitches generally developed cokes of slightly higher average crystallite sizes than the pitches of petroleum origin. The microstructure of the coal-tar pitch cokes is probably influenced by the amount and nature of the QI fraction. For the petroleum pitches there was a tendency that a high average crystallite size was connected to a more well-developed structure (larger domains) at the green coke stage. The evaluation of hydrogen donor and acceptor abilities provides a rapid and relatively simple method to differentiate pitches which can be linked to the development of structure during carbonization. These properties thus reflect the thermal reactivity of pitches and can be connected to the release of volatiles during pyrolysis. However, for coal-tar pitches the QI content was found to be the most influential factor on the development of optical texture and must be considered in addition to the hydrogen transfer properties. Considerations on thermal reactivity from NMR spectroscopy and elemental analysis were found to generally support the results from the hydrogen donor and acceptor ability tests.

The main objectives of the thesis work were: (1), to study the oxidation of methanol and formic acid on platinum electrodes by employing conventional and advanced electrochemical methods, and (2), to develop membrane electrode assemblies based on polybenzimidazole membranes that can be used in fuel cells up to 200 °C. D.c. voltammetry and a.c. voltammetry studies of methanol and formic acid on polycrystalline platinum in sulphuric acid electrolyte were performed to determine the mechanism and kinetics of the oxidation reactions. A combined potential step and fast cyclic voltammetry experiment was employed to investigate the time dependence primarily of methanol oxidation on platinum. Charge measurements clearly demonstrated the existence of a parallel path at low potentials and short times without formation of adsorbed CO. Furthermore, experimental results showed that only the serial path, via adsorbed CO, exists during continuous cycling, with the first step being diffusion controlled dissociative adsorption of methanol directly from the bulk electrolyte. The saturation charge of adsorbed CO derived from methanol was found to be significantly lower than CO derived from formic acid or dissolved CO. This was attributed to the site requirements of the dehydrogenation steps, and possibly different compositions of linear, bridged or multiply bonded CO. The coverage of adsorbed CO from formic acid decreased significantly at potentials just outside of the hydrogen region (0.35 V vs. RHE), while it did not start to decrease significantly until about 0.6 V vs. RHE for methanol. Adsorbed CO from dissolved CO rapidly oxidized at potentials above about 0.75 V due to formation of platinum oxide. Data from a.c. voltammograms from 0.5 Hz up to 30 kHz were assembled into electrochemical impedance spectra (EIS) and analyzed using equivalent circuits. The main advantages of collecting EIS spectra from a.c. voltammetry experiments are the ability to directly correlate the impedance spectra with features in the corresponding d.c. voltammograms, and the ability to investigate conditions with partially covered surfaces that are inaccessible in steady-state measurements. A variety of spectral types were observed, and for methanol these showed only a single adsorption relaxation aside from the double-layer/charge-transfer relaxation, though some structure in the phase of the latter relaxation hints at another process. The charge-transfer resistance showed Tafel behaviour for potentials in the rising part of the oxidation peak consistent with a one-electron process in the rate-determining step. The rate limiting step was proposed to be the electrochemical reaction between adsorbed CO and OH at the edge of islands of OH, with competition between OH and CO adsorption for the released reaction sites. Only a single adsorption relaxation in methanol oxidation was observed, implying that only one single coverage is required to describe the state of the surface and the kinetics. It was assumed that this single coverage is that of OH, and all the surface not covered with OH is covered with CO so that the coverage of CO is not an independent variable. Inductive behaviour and negative relaxation times in the methanol oxidation were attributed to nucleation and growth behaviour. Linear voltammetry reversal and sweep-hold experiments also indicated nucleation-growth-collision behaviour in distinct potential regions, both in the forward and reverse potential scan for methanol oxidation on platinum. In both methanol oxidation and formic acid oxidation, a negative differential resistance (NDR) was observed in the potential regions that possess a negative d.c. polarization slope, and was attributed to the formation of surface oxide which inhibited the oxidation of methanol or formic acid. EIS spectra for formic acid clearly showed the presence of an additional low frequency relaxation at potentials where we expect adsorbed dissociated water or platinum oxide to be present, implying that more than one single coverage is required to describe the state of the surface and the kinetics. Two potential regions with hidden negative differential resistance (HNDR) behaviour were identified in the positive-going sweep, one prior to platinum oxide formation, assumed to involve adsorbed dissociated water, and one just negative of the main oxidation peak, assumed to involve platinum oxide. Oscillatory behaviour was found in the formic acid oxidation on platinum by adding a large external resistance to the working electrode circuit, which means that there is no longer true potentiostatic control at the interface. By revealing the system time constants, impedance measurements can be used to assist in explaining the origin of the oscillations. In the case of formic acid, these measurements showed that the oscillations do not arise from the chemical mechanism alone, but that the potential plays an essential role. Preparation and optimization of gas-diffusion electrodes for high temperature polymer electrolyte fuel cells based on phosphoric acid doped polybenzimidazole (PBI) membranes was performed. This fuel cell allows for operating temperatures up to 200 °C with increased tolerance towards catalytic poisons, typical carbon monoxide. In this work we employed pure hydrogen and oxygen as the fuel cell feeds, and determined the optimum morphology of the support layer, and subsequently optimized the catalytic layer with respect to platinum content in the Pt/C catalyst and PBI loading. A smooth and compact support layer with small crevices and large islands was found to be beneficial with our spraying technique in respect to adhesion to the carbon backing and to the catalyst layer. We found that a high platinum content catalyst gave a significantly thinner catalyst layer (decreased porosity) on both anode and cathode with superior performance. The PBI loading was found to be crucial for the performance of the electrodes, and a relatively high loading gave the best performing electrodes.

In the past more and more advanced and fine-tuned processes for steel production have resulted in increased demands for new and more costeffective ferroalloys used as constituents in the processes. Casting techniques and equipment are continually studied for potential improvements. In order to ensure a high and consistent quality in the alloys and the casting equipment, the heat transfer from the alloy to the mould during casting must be understood. Research on free metal flows is scarce and to remedy this a doctoral study at the Norwegian University of Science and Technology was initiated. The study was limited to the region around the impingement point of the metal jet, because this is the critical area for both heat and mass transfer. The flow develops radially, first as a thin film spreading evenly over the surface. At a certain point the thickness of the film increases suddenly - known as a hydraulic jump. Only steady-state conditions on a flat plate (without accumulation of fluid) are studied. The jump develops before the flow reaches the edge of the plate and maintains this position until steady-state conditions are obtained. This system is believed to be a good approximation for the initial conditions during the filling of an open mould. This is also the period when the thermal load on the mould is greatest. Numerous practical and mathematical simulations have been carried out and a relatively simple analytical model depicting the surface rofile of the liquid metal including heat transfer to the surroundings has been developed. The computational fluid dynamics code FLUENT was also used to compute the surface profile with the Volume-Of-Fluid technique, but with little success. The code was instead used to determine the flow and temperature fields inside the already established surface profile.Various laminar and turbulent flow models (variations of the k - εmodel) were tried and compared. Experiments with water were carried out for studying the flow field. Tin was used for heat transfer studies. Finally, these simulations were compared with results from the practical experiments. Introductory experiments were carried out with ferrosilicon with the intent to perform complete experiments with this metal.Measured heat flow usually exceeded predicted values, particularly in the stagnation region. Good agreement is shown between the results from the FLUENT simulations and the new analytic model, which shows good promise of acting as a useful alternative to the much more demanding numerical simulations.

An apparatus to measure compressive creep in carbon materials has been developed. Using the final experimental set-up five material properties could be measured in each electrolysis experiment. Creep, sodium expansion, compressive strength and E-modulus were measured for 3 commercial cathode materials at 25 and 980 °C with and without electrolysis. The sodium diffusion coefficient (D) was calculated from the sodium expansion results. Filler materials for cathode blocks, i.e., certain anthracite and petrol coke qualities, were exposed to sodium vapour to examine crack evolution. Creep The three commercial cathode materials were found to deform with time under compression at 25 °C, 980 °C and during electrolysis at 980 °C. Only samples from one block for each quality was studied, so care must be taken before extending the ranking to all classes of cathode materials. The ranking from low to high creep at 980 °C and during electrolysis was: Semigraphitized < Anthracitic < Semigraphitic The creep is larger during electrolysis than at 980 °C for all materials and the increase in creep from virgin to electrolysed material at 980 °C is largest for the anthracitic material. Repeated loadings did not influence the shape of the creep strain curve, which could be described by the expression (time)n. The magnitude of the creep strain ranged from 0.01 to 0.07 % with a load of 20 MPa held for one hour. The largest measured creep was approximately 0.35 % after 20 hours of electrolysis in the semigraphitic material. The stress-strain diagram of the anthracitic material is unchanged before and after electrolysis and exhibits a more linear behaviour than in the other materials. The stress-strain diagram of the semigraphitic and semigraphitized materials changes after loading and tend to increase after electrolysis. Cracks All anthracite grains cracked to some extent after being exposed to sodium vapour at 800 °C. The lowest heat treated grains cracked the most. Cracks through grains were also found in the commercial material during electrolysis. In the petrol cokes only grains calcined to 1500 °C with a structure characterised by a gradient from mosaic to flow was observed to crack after exposure to sodium vapour at 800 °C. Diffusion coefficient The diffusion coefficient of sodium in carbon during electrolysis has been calculated with three different solutions of Fick’s law and is found to increase with current density and graphitic character of the material. Two of the calculations were based on the expansion of the sample (penetration from bottom and radial penetration) and one on a rather few measured sodium concentrations. The diffusion coefficient was calculated to be in the range 8-10-5 to 5-10-4 cm2/s at current densities from 0.06 to 0.88 A/cm2, which is around 10 times larger than reported before (Table 2.1). The cryolite ratio did not influence D as the saturation time for samples in acidic or basic melt was the same. The ranking from larger to smaller diffusion coefficient in the studied materials was Semigraphitized > Semigraphitic > Anthracitic The diffusion coefficient increased with heat treatment temperature in some laboratory produced materials.

In this study, the oxygen permeation and stability properties of disk shaped and asymmetric membranes, both of the composition La0.2Sr0.8Fe0.8Al0.2O3-δ were investigated. Strontium doped Lanthanum ferrite is an oxygen deficient mixed ionic electronic conducting perovskite related material. Co-doping with Aluminum enhances the stability of the system. Received precursor was ball milled and sieved to 250 µm. Phase purity was determined by means of X-ray diffraction. Further on particle size distribution and surface area data were collected by dynamic light scattering and nitrogen absorption (BET).Ceramic disks were fabricated by dry uniaxial dye pressing and sintered at different temperatures. Densities of green bodies were measured by geometric means to be approximately 40% of theor. and final densities were measured using Archimedes method. to be approximately 96% of theor. at a sintering temperature of 1230 °C for 2 h in air.Asymmetric membranes consist of a porous support and a dense functional layer. For preparation of porous supports the powder precursor was mixed with 30 wt-% carbon black and 3 wt-% ethyl cellulose. Supports were calcined at 950 °C and then dip coated with a stabilized suspension of La0.2Sr0.8Fe0.8Al0.2O3-δ in ethanol. After dip coating, membranes were pre sintered at 1100 °C, dip coated again and finally sintered at different temperatures. Visual densities were investigated by scanning electron microscopy. Final sintering parameters were 1230 °C for 2 h respectively. Furthermore, investigations on surface modification were carried out by wet chemical etching using 6M hydrochloric acid, resulting in a partly or complete dissolved functional layer.Oxygen flux of membranes was finally measured in a flux furnace with coupled gas chromatograph.Disk shaped membranes reached oxygen flux values up to 1.77 ml*min-1*cm-2 and asymmetric membranes up to 15.33 ml*min-1*cm-2. After flux measurements were completed, the membranes were checked for degradation by means of XRD and SEM/EDS. Both, disk shaped and asymmetric membranes were overall single phase but showed some morphological degradation.

A study of strain path related effects on recrystallisation in aluminium has been carried out. The recrystallisation process has been studied after deformation in torsion and one pass hot rolling. For both deformation models, the work has been a combination of experimental studies of the deformation microstructure and recrystallisation process, as well as use of models for prediction of the deformation- and recrystallisation process. For deformation in torsion AA1050 and AA3103 has been studied. Cyclic deformation to zero net strain resulted in restoration of the initial grain structure, while monotonic deformation yielded an increasingly more elongated grain structure. Studies by EBSD revealed no difference in subgrain size as function of strain path, but the subgrain misorientation was larger after monotonic deformation. Similarly, the distance between high angle boundaries was smaller after monotonic deformation. The recrystallised grain size was larger after cyclic deformation, compared to monotonic deformation to the same cumulative strain. In AA1050 the difference in recrystallised grain size was mainly sees as an effect of difference in grain boundary area, leading to fewer nuclei after cyclic deformation. A small difference in driving pressure also contributed to the difference in recrystallised grain size. In AA3110 an additional effect of weakening of deformation zones surrounding particles was purposed, resulting in lower density of PSN-nuclei after cyclic deformation and accordingly larger grain size. The experimental study of the hot rolling pass was performed on an AA3103 alloy. A slight increase in Vickers hardness was seen from center to surface of the rolling slab after deformation. The microstructure after rolling was predicted by a combination of FEM-simulations and a microstructure model. This approach resulted in a larger predicted gradient in flow stress through thickness than calculated from the hardness measurements. The recrystallisation kinetics were monitored and were found to be fastest in the surface areas. The experimentally measured gradient in recrystallisation kinetics from center to surface was much larger than what was modeled. This was seen as an effect of the models limited coverage of changes in the density of nuclei as a result of other mechanisms than a difference in the driving pressure.

<p>The present work has been carried out in order to investigate Al-Mg-Si alloys that are deformed at moderate temperatures. These temperatures are in the range between 200 C and 300 C. Also some experiments are performed at room temperatures. Two deformation models have been applied in the experiments: material deformation by compression testing and by forward extrusion. </p><p>The investigated alloys are AA6063, AA6082 and an alloy that is named “Alloy R” in this work. The latter alloy is the industrial alloy AA6082 without the Mn-addition (0.56wt%Mn in the AA6082). The “R” denotes the recrystallized microstructure in the material after hot forming operations.</p><p>The investigations show the effect of changing the temperature in the given temperature interval on the stress-strain relationship for each alloy. From the compression testing, it is found that none of the alloys AA6063 or Alloy “R” reaches a steady state condition as true strain approaches 0.8 for deformation temperatures between 200 C and 250 C. At compression testing performance at 300 C, the alloy “R” reaches a steady state condition at a true strain equal to 0.4.</p><p>As true stress-true strain relationship has been investigated for the “Alloy R” and the AA6063 at comparable deformation parameters, it is shown that the alloy “R”, with the highest Si-content, requires the highest true stress for a given true strain value (AA6063: 0.45wt%Si, Alloy “R”: 0.87wt%Si).</p><p>From the compression testing, the effect of Mn on the material properties in the AA6082-alloy has been determined. For the Alloy “R” and the AA6082, the true stress reached the same value after a certain amount of deformation. As deformation temperature increases, this common value of true stress corresponds to a decrease in true strain.</p><p>The AA6082 and Alloy “R” are also compared in experiments performed in forward extrusion. One observes that for the same deformation temperature and at identical die diameters, the ram force is identical. It is worth noticing that these alloys did not show the same relationship during the compression testing at low values of true strain (<0.8). On a microscopic scale, one concludes that Mn has no significant effect on the stress-strain relationship for the applied deformation parameters in the forward extrusion equipment.</p><p>Hardness measurements indicate that the age hardening potential in the extruded test specimen decreases as the deformation temperature increases. The hardness data is similar for both the AA6082 and the Alloy R, thus indicating that the Mn content has no significant effect on the strength of the material.</p><p>The deformed material has been annealed in order to investigate the recrystallization process in the AA6082 and the Alloy “R”. The recrystallization grain size in the Alloy “R” is significantly larger than in the AA6082 at comparable deformation parameters after annealing at 530 C for 15 minutes. This result is due to the effect of Mn-containing dispersoids in the AA6082. The recrystallization grain size in the Alloy “R” seems to be unaffected by the deformation temperature after annealing for 15 minutes. The observation of the AA6082 is quite different. A small increase in grain size is observed for both reduction ratios as the deformation temperature is elevated from 20C to 200 C and further to 250 C. At extrusion temperatures of 300 C the recrystallization grains are significantly larger.</p><p>Annealing experiments performed at 430 C on the AA6082 indicates that a change in the deformation temperature from 200 C to 250 C does not affect the amount of stored energy in the material significantly.</p><p>The Forge2 programme has been used to perform numeric simulations of the forward extrusion experiment. From this the temperature distribution, strain rate variation and true strain development in the test piece had been investigated. As the simulated true strain values are compared to the grain size in the annealed material, the recrystallization grain size is related to the amount of stored energy in the material in a very convincing way. It is also shown that the recrystallization grain diameter is related to the amount stored energy as the grain diameter is investigated in the radial and the extrusion direction separately.</p>

The present work has been carried out in order to investigate Al-Mg-Si alloys that are deformed at moderate temperatures. These temperatures are in the range between 200 C and 300 C. Also some experiments are performed at room temperatures. Two deformation models have been applied in the experiments: material deformation by compression testing and by forward extrusion. The investigated alloys are AA6063, AA6082 and an alloy that is named “Alloy R” in this work. The latter alloy is the industrial alloy AA6082 without the Mn-addition (0.56wt%Mn in the AA6082). The “R” denotes the recrystallized microstructure in the material after hot forming operations. The investigations show the effect of changing the temperature in the given temperature interval on the stress-strain relationship for each alloy. From the compression testing, it is found that none of the alloys AA6063 or Alloy “R” reaches a steady state condition as true strain approaches 0.8 for deformation temperatures between 200 C and 250 C. At compression testing performance at 300 C, the alloy “R” reaches a steady state condition at a true strain equal to 0.4. As true stress-true strain relationship has been investigated for the “Alloy R” and the AA6063 at comparable deformation parameters, it is shown that the alloy “R”, with the highest Si-content, requires the highest true stress for a given true strain value (AA6063: 0.45wt%Si, Alloy “R”: 0.87wt%Si). From the compression testing, the effect of Mn on the material properties in the AA6082-alloy has been determined. For the Alloy “R” and the AA6082, the true stress reached the same value after a certain amount of deformation. As deformation temperature increases, this common value of true stress corresponds to a decrease in true strain. The AA6082 and Alloy “R” are also compared in experiments performed in forward extrusion. One observes that for the same deformation temperature and at identical die diameters, the ram force is identical. It is worth noticing that these alloys did not show the same relationship during the compression testing at low values of true strain (&lt;0.8). On a microscopic scale, one concludes that Mn has no significant effect on the stress-strain relationship for the applied deformation parameters in the forward extrusion equipment. Hardness measurements indicate that the age hardening potential in the extruded test specimen decreases as the deformation temperature increases. The hardness data is similar for both the AA6082 and the Alloy R, thus indicating that the Mn content has no significant effect on the strength of the material. The deformed material has been annealed in order to investigate the recrystallization process in the AA6082 and the Alloy “R”. The recrystallization grain size in the Alloy “R” is significantly larger than in the AA6082 at comparable deformation parameters after annealing at 530 C for 15 minutes. This result is due to the effect of Mn-containing dispersoids in the AA6082. The recrystallization grain size in the Alloy “R” seems to be unaffected by the deformation temperature after annealing for 15 minutes. The observation of the AA6082 is quite different. A small increase in grain size is observed for both reduction ratios as the deformation temperature is elevated from 20C to 200 C and further to 250 C. At extrusion temperatures of 300 C the recrystallization grains are significantly larger. Annealing experiments performed at 430 C on the AA6082 indicates that a change in the deformation temperature from 200 C to 250 C does not affect the amount of stored energy in the material significantly. The Forge2 programme has been used to perform numeric simulations of the forward extrusion experiment. From this the temperature distribution, strain rate variation and true strain development in the test piece had been investigated. As the simulated true strain values are compared to the grain size in the annealed material, the recrystallization grain size is related to the amount of stored energy in the material in a very convincing way. It is also shown that the recrystallization grain diameter is related to the amount stored energy as the grain diameter is investigated in the radial and the extrusion direction separately.