O objetivo deste trabalho foi determinar a influência do ferro e do manganês em uma liga de alumínio com 9% de silício (% em peso). Para isto, foram elaboradas duas famílias de liga Al-9%Si: uma com os teores de 0,1%, 0,4%, 0,8% e 1,2% de Fe e uma segunda liga de Al-9%Si-0,8%Fe com teores de 0,1%, 0,4% e 0,7% de Mn. Para a realização deste estudo, foram produzidos corpos de prova de tração fundidos em coquilha, segundo a norma ASTM B108. Os corpos de prova obtidos foram tracionados para avaliação das propriedades mecânicas, em seguida, foram submetidos a uma análise microestrutural por microscopia óptica (MO) e eletrônica de varredura (MEV). As superfícies de fratura dos corpos de prova tracionados foram também observadas por MEV com a finalidade de comparar o efeito das adições de Fe e Mn. O efeito da adição crescente de Fe na liga Al-9%Si foi observado no ensaio de tração que mostrou queda tanto nos limites de resistência e de escoamento como no alongamento, decorrentes da formação da fase β-Al5FeSi que apresentou morfologia em plaquetas, interrompendo a continuidade da matriz de alumínio. Para teores abaixo de 0,4% de Fe, ocorreu um ligeiro aumento da resistência mecânica que pode ser atribuído à formação da fase α-Al8Fe2Si, que apresentou morfologia tipo escrita chinesa, que não interrompe a continuidade da matriz. Com adição de teores crescentes de Mn na liga Al-9%Si-0,8%Fe ocorreu uma elevação do limite de resistência e do alongamento, mas uma queda do limite de escoamento, quando comparados com a mesma liga sem adição de Mn. Conclui-se que esse comportamento pode ser atribuído a mudança de morfologia do intermetálico de plaquetas para escrita chinesa que intercala a matriz dúctil com a fase frágil, devido a adição do Mn. / This study aims to determine the influence of iron and manganese in an aluminum alloy with 9% silicon (% by weight). Were prepared two families of alloy Al-9%Si: one with the content of 0.1%, 0.4%, 0.8% and 1.2% Fe and a second alloy of Al-9% Si-0,8%Fe content of 0.1%, 0.4% and 0.7% Mn. For this study, tensile specimens were produced in permanent mold casting according to ASTM B108. The specimens obtained were pulled for quantitative evaluation of the mechanical properties and were subjected to a qualitative metallographic evaluation. Qualitative analysis of the bodies of tensile fracture test was conducted in order to compare the effect of additions of Fe and Mn. The effect of incremental addition of Fe in the alloy Al-9% Si was observed in the tensile test that showed a decrease in both the tensile and elongation flow as resulting from the formation of β-Al5FeSi phase platelet morphology showed that interrupting the continuity of aluminum matrix. To levels below 0.4% Fe, there was a slight increase in strength can be attributed to the formation of α-Al8Fe2Si phase morphology presented in chinese script that does not interrupt the continuity of the matrix. With addition of increasing concentrations of Mn in the alloy Al-9% Si-0, 8% Fe was an increase in the tensile strength and elongation but fall of yield stress when compared to the same alloy without Mn addition. We conclude that this behavior can be attributed to a change in morphology of the intermetallic platelets to chinese writing interspersing the ductile matrix with brittle phase due to the addition of Mn.

O presente trabalho apresenta um estudo sobre o amolecimento após laminação e recozimento da AA 7075, uma liga de alumínio endurecível por precipitação . As amostras recebidas no estado T6 foram caracterizadas com auxílio das técnicas de microscopia óptica de luz polarizada, microscopia eletrônica de varredura, espectroscopia de raios X por dispersão de energia, difração de raios X, condutividade elétrica e dureza Vickers . As amostras foram então separadas em dois grupos. O primeiro sofreu um tratamento térmico de solubilização (485°C por 5 horas) enquanto o segundo foi submetido a um tratamento de superenvelhecimento (300°C por 5 horas) e, em seguida, ambos os grupos de amostras tratadas foram novamente caracterizadas pelas técnicas descritas anteriormente (exceto microscopia óptica) e laminadas a frio. Durante a etapa de laminação, constatou-se a dificuldade em causar deformação plástica na amostra solubilizada. Optou-se em conduzir o estudo com as amostras superenvelhecidas, que foram laminadas com reduções de 45%, 75% e 90% em espessura. A seguir, estas foram submetidas a tratamentos isotérmicos e isócronos com o objetivo de estudar a cinética de amolecimento das amostras deformadas a frio. As amostras superenvelhecidas e deformadas em 45% em redução de espessura, apresentaram somente indícios de início de recristalização (nas amostras tratadas a partir de 250°C por 1 hora) via EBSD, sendo que a maior parte do amolecimento pode ser explicada pelo mecanismo de recuperação. Além disso, a cinética de amolecimento das amostras recozidas nesse grupo apresentaram boa concordância com a lei logarítmica proposta por Kulhmann (1948) e (coincidentemente) também com o consolidado modelo JMAK. As amostras superenvelhecidas e deformadas em 75% e 90% apresentaram comportamento similar (isso é, principalmente recuperação) para recozimentos realizados em temperaturas de até 350°C por uma hora. Recozimentos realizados a 400°C promoveram a recristalização total das amostras desse grupo para tempos inferiores a 15 minutos. Dessa forma, não foi possível estudar a cinética de recristalização para esse segundo grupo de amostras. / This work presents a study about the softening after cold rolling and annealing of aluminium alloy AA 7075. Firstly, polarized light optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, electrical conductivity and Vickers hardness have been used at the starting material (T6). The samples were then separated in two groups. The former underwent a solubilization heat treatment (485°C for 5 hours) whilst the latter underwent an overaging treatment to grow up the existing precipitates (300°C for 5 hours). Both groups of treated samples were again characterized by the techniques described above (except optical microscopy). In the rolling stage, the difficulty in straining the solubilized sample and the relative ease for doing so to the overaged sample was verified. It was therefore decided to conduct the study with the samples of the second group, which were 45%, 75% and 90% rolled in thickness reduction. Then, they underwent isothermal and isochronous treatments in order to study its softening kinetics by Vickers hardness measurements, polarized light optic microscopy and EBSD. The overaged and rolled samples (45% in thickness reduction) didn\'t present evidences of recrystallization except by very few grains found via EBSD (in samples treated from 250 ° C for 1 hour). So, most of the observed softening can be explained by recovery. In addition, the softening kinetics of the annealed samples in this group showed good agreement with the logarithmic law proposed by Kulhmann (1948) and (coincidentally) also with the consolidated JMAK model. The overaged samples that underwent thickness reduction of 75% and 90% showed a similar behavior (that is, mainly recovery) for annealing at temperatures up to 350 ° C. Annealing at 400 ° C promoted total recrystallization of the samples from this group (75% and 90% in thickness reduction) in less than 15 minutes. Thus, it was not possible to study the kinetics of recrystallization for this second group of samples.

The effect of high temperature, high strain rate deformation on the evolution of second phase particles in commercial aluminium alloys has been investigated. Three model alloys provided by Novelis have been examined, and the evolution of particles during deformation has been examined for the alloy that most closely resembles the composition of alloys used in commercial applications. The effect of deformation mechanisms was expected to be an enhancement of diffusion controlled processes; therefore the first part of the work was to develop a heat treatment that would produce a fine distribution of dispersoid particles. This heat treatment was then used to prepare material for torsion testing, at strain rates similar to those found during the hot rolling stage of commercial production. Testing was performed at both the end of heat treatment temperature, to remove thermal effects, and at a lower temperature which more closely represents the temperature during commercial rolling. Material was examined by optical microscopy, FEGSEM and TEM and the particle populations were characterised by backscattered FEGSEM imaging and image analysis. This demonstrated that the disperoid particle population develops in multiple ways. Along with the enhancement of coarsening there is a significant shape change to the dispersoid particles, suggesting a change in the character of their interface. It has also been demonstrated that there is nucleation of new particles, despite a long prior hold time, in material deformed at the same temperature as the heat treatment. Material deformed at lower temperatures also demonstrated a larger increase in the volume fraction of dispersoid than material with the same thermal history. A constitutive model for diffusion enhancement and a model for particle evolution have been combined to simulate the effects of thermomechanical processing on the particle population.

No description available.

Aluminium salen and aluminium salan complexes are excellent catalysts for the ring-opening polymerisation of lactide. This thesis studied their efficacy in the polymerisation of novel monomers and their ability to build new macrostructures. Aluminium salen and aluminium salan complexes were tested as catalysts for ring-opening polymerisation of common aliphatic monomers where controlled polymer synthesis has not yet been achieved with similar systems. Excellent control over molecular weight and dispersity was achieved for β-caprolactone polymerisation, with high molecular weights accessible. Immortal polymerisation could also be performed with an extremely high level of chain transfer agent (up to 100 equivalents) and the highest monomer turnover (10000 monomer equivalents) with aluminium salen catalysts to date. Addition of functional groups to the monomer was also studied; the effect of steric bulk in polymerisation of methylsubstituted derivatives was significant. Protected alcohol functionalities can also be introduced into easily synthesised homopolymers and copolymers. The first example of synthesising a polyester with aromatic functionality within the polymer backbone via polymerisation of cyclic ester monomers was studied with an aluminium salen catalyst. 2,3-Dihydro-5H-1,4-benzodioxepin-5-one polymerisation was facile and proceeded under mild conditions. The resulting polymer could be depolymerised back to starting monomer with the same aluminium salen catalyst under dilute conditions. Random, AB diblock and ABA triblock copolymers were readily synthesised with L-lactide and β-butyrolactone as comonomers. Block copolymers with β-butyrolactone could also be selectively depolymerised, to give poly(3-hydroxybutyrate) homopolymers. Attempted polymerisation of a range of other aromatic monomers was unsuccessful due to addition of steric bulk, changing orientation of the monomer ester bond or decreasing the ring size. Synthesis of homopolymer and ABA triblock copolymers with L-lactide and alkyl-substituted β-lactones was investigated. Homopolymerisation of all alkyl-substituted β-lactones resulted in well controlled polymer, with rate decreasing as alkyl-substituent length increased. A sequential addition of monomers method with β-butyrolactone, β-valerolactone and β-heptanolactone was employed for copolymer synthesis. Copolymers synthesised from β-butyrolactone and β-valerolactone resulted in tunable glass transition and melting temperatures. Copolymers synthesised from β-heptanolactone resulted in thermoplastic elastomers exhibiting microphase separation, supported by differential scanning calorimetry and small-angle X-ray scattering. Finally, optimisation of in situ generated carbonylation catalysts was studied. Optimisation of literature complexes allowed for synthesis of β-valerolactone, β- heptanolactone, β-tridecalactone, 4-chloro-β-butyrolactone and β-6-heptenolactone on relatively large scales under much easier experimental protocols. Additionally, tuning of ortho-phenylene bridged salen ligand framework gave to structure-activity relationships. Using this optimised catalyst system, 4-chloro-β-butyrolactone and β- 6-heptenolactone were prepared and used in ring opening polymerisation. Well controlled and efficient polymerisation of 4-chloro-β-butyrolactone was easily achieved with aluminium salen and salan catalysts. Homopolymers and block copolymers with poly(ethylene glycol) and β-6-heptenolactone were readily synthesised.

The industrial use of recycled aluminium is greatly limited by the degraded mechanical properties due to the increased impurities. Fe, one of the common impurity content in Al alloys, is difficult to eliminate once introduced into aluminium during primary production or recycling processes. Due to the low solid solubility of Fe in Al, the formation of Fe-rich intermetallic compounds (Fe-IMCs) is inevitable, which is one of the main causes for the deterioration of mechanical properties in various cast Al alloys. In order to obtain desirable mechanical properties of recycled Al alloys, modification and refinement of the Fe-IMCs are urgently required as the compact and refined morphologies of such intermetallics are generally non detrimental to Al alloy's performance. However, manipulating the solidification behaviour of the Fe-IMCs phases, including nucleation and growth, is very challenging because of the inherently more difficult heterogeneous nucleation of the Fe-IMCs compared with that of a pure metal or a solid solution; and the strong growth anisotropy. Limited understanding on mechanisms of nucleation and growth of the multicomponent Fe-IMCs is available in the literature. The aim of this study is to gain a deeper understanding on the heterogeneous nucleation and growth behaviour of Fe-IMCs in various Al alloys. The nucleation and growth of both primary and eutectic Fe-IMCs have been investigated during various solidification conditions including a number of different cooling rates and casting temperatures. Based on the experimental results of the solidification of several ternary and quaternary alloys, effect of Mg on the solidification behaviour of Fe-IMCs was investigated. Further the surface modified TiB2 particles were used to enhance the heterogeneous nucleation of Fe-IMCs in order to refine the Fe-IMCs particles. The dominant Fe-IMC in Al-5Mg-2Si-1.2Fe-0.7Mn alloy is identified, using transmission electron microscopy (TEM), as α-AlFeMnSi with a body centred cubic (BCC) lattice structure and lattice parameter of 1.256nm. In the current alloy system, the nucleation of primary α-AlFeMnSi occur at lower cooling rate (≤0.8K/s) when required nucleation undercooling is reached, as the slower cooling rate allows longer diffusion time for the solute to form a stable nucleation embryo. When casting with 20K superheat, the size of primary α-AlFeMnSi increases gradually from 24.5±3.1μm (870K/s) to 251.3±75.3μm (0.02K/s) and the size of α-AlFeMnSi eutectic increased gradually from 102.0μm (870K/s) to 623.3μm (0.02K/s). The Fe and Mn concentration in α-AlFeMnSi appears to reduce with the increased cooling rate due to the relatively insufficient solute supply when solute concentration is low (1.2wt.% Fe and 0.7wt.% Mn). Microstructure observation reveals that the {011} plane, especially on <111> orientation, is the preferred growth orientation of BCC primary α-AlFeMnSi, resulting in rhombic dodecahedral in 3D. The eutectic α-AlFeMnSi, prefers to initiate on the primary α-AlFeMnSi. In addition to the substantial nucleation undercooling, the research revealed that the nucleation of primary α-AlFeMnSi also rely on the local solute concentration and the solute diffusion. Compared with α-Al, the growth of α-AlFeMnSi is less sensitive to the cooling rate changes due to the complexities in multi-components interaction and different diffusion efficiency of different elements. The addition of Mg to Al-1.2Fe-0.7Mn and Al-2Si-1.2Fe-0.7Mn alloys was found to lead to a morphology change of Fe-IMCs. Al6(Fe,Mn), the predominant Fe-IMC in the Al-1.2Fe-0.7Mn-xMg alloy, changed from needle morphology to interconnected lamellar morphology when Mg composition increased from 0.004wt.% to 6.04wt%. A Mg-rich layer at about 5-20nm in thickness was commonly observed on the Fe-IMC/α-Al interface in the alloys with Mg content. The eutectic lamellar spacing for Al6(Fe,Mn) increases from 1.8±0.3μm to 4.5±0.8μm when Mg content increased from 0.004wt.% to 6.04wt.%. In the case of α-Al12(Fe,Mn)3Si, the predominant Fe-IMC in Al-2Si-1.2Fe-0.7Mn-yMg alloys, its lamellar spacing of the eutectic increased from 1.4±0.3μm to 3.25±0.8μm when Mg increased from 0.04wt.% to 5.41wt.%. Owing to the strong anisotropy of the Fe-IMC crystals, the segregation of solute Mg on preferred growth orientation is higher, causing greater growth restriction on this orientation. Consequently, the growth velocity on other orientations becomes relatively more significant. To optimise the morphology of Fe-IMCs in Al alloys, a novel Αl-Ti-B(Fe) grain refiner for Fe-IMCs has been developed to enhance the heterogeneous nucleation of Fe-IMCs. The addition of the novel grain refiner to an Al-5Mg-2Si-1.2Fe-0.7Mn alloy under controlled solidification condition results in a considerable refinement of the primary Fe-IMCs from 251.3±75.3μm to 110.9±45.5μm and from 127.3±36.2μm to 76.5±18.2μm at cooling rates of 0.02K/s and 0.15K/s, respectively. TEM investigations on the refiner reveal a Fe-rich adsorption monolayer in a zigzag fashion on the prismatic planes on the boride particles. This surface modification is beneficial for the heterogeneous nucleation of the Fe-IMCs. Further investigation of the Al alloy with this grain refiner addition revealed that there existed specific orientation relationships (ORs) between TiB2 and Fe-IMCs: (001)[020]Al13Fe4 // (11-20)[10-10]TiB2, and (001)[120]Al13Fe4 ∠6.05˚ (11-20)[10-11]TiB2; (0-11)[100]α-AlFeMnSi // (0001)[-2110]TiB2, and (0-11)[111]α-AlFeMnSi ∠4.5˚ (0001)[10-10]TiB2. The Fe adsorption on substrate particle, the observed ORs between TiB2 and Fe-IMCs, and the refinement of primary α-AlFeMnSi with the addition of modified TiB2 provide evidence of structure templating and composition templating required by heterogeneous nucleation of Fe-IMCs. This research has delivered contribution to the understanding and new approach for optimizing the morphology of Fe-IMCs in the Fe-containing Al alloys. Using the slow cooling rates (≤0.15K/s), the formation compact primary α-AlFeMnSi can be considerably encouraged. With a lower casting temperature, the size and volume fraction of large Chinese-script α-AlFeMnSi can be significantly reduced. With addition of reasonable Mg content the morphology of Fe-IMC can be modified. Particularly, with the addition of the Al-Ti-B(Fe) grain refiner in well-controlled condition, the primary α-AlFeMnSi can be significantly refined. Thus, by implementing these approaches, the optimized Fe-IMC morphology in the microstructure of Fe-containing Al alloy is able to offer promising mechanical performance.

The reactions of carboxylic acids with organoaluminium reagents were studied, which led to the formation of novel aluminium compounds. The reactions of orthofunctionalised derivatives of benzoic acid with trivalent aluminium organyls AlR3, led to the formation of different Al-based molecular clusters, depending on the nature of R, the reaction stoichiometry and the character of the benzoic acid derivative. The obtained compounds were characterised in the solid state by X-ray diffraction methods and two main motifs were observed. When the acid and AlR3 reacted in a one-to-two stoichiometry the obtained products, [iBu4Al2(μ-O2CC6H4-2-μ- O)]2, [(Me2Al)2(μ-O2CC6H4-2-μ-NH)]2, [(iBu2Al)2(μ-O2CC6H4-2-μ-NH)]2, [(Me2Al)2(μ- O2CC6H4-2-μ-NMe)]2 and [(iBu2Al)2(μ-O2CC6H4-2-μ-NMe)]2, consisted of a central distorted 12-membered macrocycle, formed by two [Al-O-C-O-Al-X] units (X= O,N) and was found to be dimeric. The reaction between anthranilic acid derivatives and AlR3 could also take place in a one-to-one ratio. For anthranilic acid and Nmethylanthranilic acid the obtained crystals only allowed a qualitative analysis and showed the structure of the products, [MeAl(μ-O2CC6H4-2-μ-NH)]4, [iBuAl(μ-O2CC6H4- 2-μ-NMe)]4 to be tetrameric and each consisting of a distorted 16-membered ring formed by four [O-C-O-Al] units. With the reaction of N-phenylanthranilic acid it was possible to isolate a structural analogous product [iBuAl(μ-O2CC6H4-2-μ-NPh)]4 which could be fully characterised by x-ray crystallography and NMR spectroscopy. Where the quantity and quality of the obtained product was sufficient, the solution behaviour of the compounds was elucidated by multinuclear and multidimensional NMR spectroscopic techniques. The 27Al NMR showed that the aforementioned aggregates are maintained in solution, which for the 12-membered [Al-O-C-O-Al-N] macrocycle of [(iBu2Al)2(μ-O2CC6H4-2-μ-NH)]2 was confirmed by a NOESY spectrum. The second part of this project focused on the preliminary studies towards the application of aluminium compounds in the crosslinking of guar and carboxymethyl hydroxypropyl guar, which are common additives in hydraulic fracturing. Different commercially available aluminium compounds were tested for their general ability to crosslink the aforementioned polysaccharides, yielding promising results for aluminium lactate, aluminium acetylacetonate and aluminium isopropoxide. For the system comprising aluminium lactate in combination with CMHPG, rheological studies were carried out to determine the viscosity, the viscoelasticity, the shear recovery and the stability towards high temperatures. These sought to evaluate the crosslinking properties of the aluminium additive and to optimise the required conditions of the different system components. Finally, it was possible to obtain first proof-of-concept data suggesting that synthetically obtained aluminium compounds such as [Me2Al(μ- O2CPh)]2 and Al[MeC(CH2O)3]2(AlMe2)3 can be employed for the crosslinking of guar and CMHPG.

A new but relatively simple processing study was conducted to investigate the microstructure-property relationships of alumina/aluminium titanate (AAT) composites. The objectives of this study were: (a) to develop a process for fabricating AAT and β-spodumene modified AAT composites using a solid-state reaction method and functionally-graded AAT using an infiltration technique, and (b) to evaluate the effects of dispersed aluminium titanate (AT) on the phase relations, microstructure and mechanical properties of alumina-based composites. The study has revealed that the processing procedures played an important rule in the microstructural development of AAT composites. The microstructure and properties of AAT composites have been found to be strongly influenced by the presence of dispersed AT. The phase relations in the AAT system have been characterised by x-ray diffraction (XRD) and neutron diffraction (ND). Rietveld analysis showed that the AT content increased in proportion with the amount of rutile added. The dynamic ND study showed that AT commenced to form at ~1310°C The presence of AT caused a reduction of hardness but an improvement in fracture toughness. In addition, the presence of AT hindered the processes or kinetics of sintering and densification. The use of β-spodumene has been investigated as a liquid-phase-sintering aid for the densification of AAT composites. XRD, ND, differential thermal analysis (DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Vickers indentation were used to characterise the effect of β-spodumene on the phase relations, densification, microstructure and mechanical properties of AAT composites. The presence of β-spodumene was found to have a profound influence on the phase relations, densification, microstructure and properties of AAT composites. / The addition of β-spodumene caused a small reduction of AT content and a commensurate increase of alumina phase. Functionally-graded AAT composites have been successfully synthesised through infiltration of porous alumina preform with a solution containing TiCl4. The infiltration kinetics of liquid into porous alumina preform has also been investigated and modelled. It was found that the infiltration rate equation proposed by Washburn was proven to be suitable for describing the kinetics of infiltration in terms of preform sintering temperature, viscosity, and multiple infiltrations. The influence of applied pressure was consistent with the model proposed by Travitzky and Shlayen, where the applied pressure enhanced the rate of infiltration. Pre-sintering of alumina preform at 900, 1000 and 1100°C for 2 h resulted in different rates of infiltration which may be attributed to a varying degree in tortuosity of the pore channels. The graded composition character of functionally-graded AAT composites has been determined by XRD and grazing incidence synchrotron diffraction (GISRD). Graded compositions from Rietveld refinement analysis showed that the concentration of AT decreased with depth. In contrast, the α-A12O3 content increased with depth. Microstructural examination by SEM showed that the content of AT grains was the most abundant near the surface and decreased gradually with an increase in depth. The hardness results showed that FGM had a soft graded-region (AT rich) but hard non-graded alumina region. / The lower hardness in the graded region can be attributed to the presence of intrinsically soft AT phase. The presence of graded AT caused a considerable improvement in damage tolerance. The isothermal decomposition of AT at 1100°C both in air and vacuum has been studied. Both ex-situ and in-situ studies have been conducted to examine the effect of environment on the decomposition behaviour of AT. The addition of MgO was effective in enhancing the thermal stability of AT against decomposition both in air and in vacuum.

Introduction of a composition gradient at a join between two materials of different elastic properties should reduce the stress concentrating effect of the interfacial discontinuity. A crack oriented perpendicular to this elasticity gradient will experience mode-mixity, and possible subsequent crack deflection. Explicit analytical solutions for the stress state at the tip of an angled crack in a graded material of a given finite geometry do not exist, and ongoing crack path development in such a gradient has not been characterised. An infiltration processing technique is developed which allows two materials to be joined through a region of graded composition, of tailored width and composition profile. Composition discontinuities at layer interfaces in a stepped gradient can be tolerated due to the resulting interpenetrating network structured (INS) microstructure. Firing stresses were found to be a limitation of the processing technique, overcome by limiting the steepness of the elastic gradient. Alumina and epoxy resin graded composites were produced and tested under monotonic loading, resulting in stable crack path evolution. Stress-field asymmetry at the tip of a crack oriented perpendicular to an elastic gradient was demonstrated, followed by subsequent crack deflection. Stress intensity factor and deflection angle increase with increasing gradient steepness. Rising R-curve behaviour was demonstrated for all compositions of the INS composite, with initiation and plateau toughness decreasing with increasing epoxy content. Evidence of crack bridging by intact ligaments of the epoxy phase in the crack wake explains this behaviour. Crack deflection towards the epoxy region was anticipated and demonstrated for all gradient configurations. An increase in relative crack depth was seen to increase mode-mixity at the crack-tip and subsequent crack deflection, up to a relative depth of ~0.5. No conclusive evidence was found for the influence of crack bridging on crack deflection. Toughness was shown to increase with the inclusion of a microstructural gradient. Measured toughness within graded samples was shown to be controlled by both the local composition and the volume of bridging ligaments in the crack wake. The optimum gradient should ??? extend over the widest region practical, ??? encompass the widest composition range possible, and ??? demonstrate extrinsic crack extension toughening.

Extrusion is a continuous solid state deformation process which is widely used in the aluminium industry. The demand for aluminium extrudates are growing and extruders are pressurized to extrude products as fast as possible without lowering the quality of the product. Important extrusion parameters and conditions are exit temperature, extrusion speed and alloy composition. It is widely accepted in extrusion industry that extrusion surface defects increase when the extrusion speed and exit temperature are increased for a constant alloy. One of the major surface defects is the so-called die pick-up and it is presently uncertain if increase with extrusion speed (from a low 25m/min) would result in an increase of the number of die pick-up defect.Die pick-up appears like a scratch mark or comet on the surface of the extrudate which damages the appearance. Previous research suggests that second phase particles, eutectic reactions (555°C - 600°C), extrusion process conditions and die conditions may influence the cause of die pick-up. However the influencing factors for die pick-up are not well established.The research started by determining the lowest melting temperature for AA6060 alloy as this temperature limit the highest temperature above which incipient melting starts. This temperature corresponds to the eutectic melting temperature for AA6060 alloy. Eutectic melting was only detected above 610°C and therefore the exit temperature could be increased to a maximum of 610°C. For an AA6xxx alloy system the lowest melting temperature is 555°C if Mg2Si and excess silicon were present. However as Mg2Si may have fully dissolved into the solid solution, no reaction can take place.A preliminary investigation was conducted to study the characteristics of the newly installed extrusion control and monitoring system. Through this study the relationship between the set extrusion speed and the actual extrusion speed was established. It was found that the actual extrusion speed was lower than the set extrusion speed and was further complicated by the capacity limit of the extrusion pressure. Exit temperature measurements were accurate, however it was measured about 1m away from the die exit. Experiments were carried out to estimate the exit temperature drop and hence the exit temperature measurements were corrected accordingly.Thus, the aim of the present research was to establish the relationship between die pick-up and extrusion conditions (extrusion speed, exit temperature and die condition) and to propose the likely formation mechanism for die pick-up.In this research AA6060 alloy was used and was extruded at 25m/min, 30m/min, 35m/min, 40m/min and 45m/min. The exit temperature was found to increases from 542°C to 567°C. Three types of die pick-up was identified which were named as normal pick-up, die line pick-up and lump pick-up. Normal pick-up occurred regardless of the extrusion speed and exit temperature; however the amount of normal pick-up did not increase when the extrusion speed was increased. Die line pick-up occurred when the extrusion speed was 45m/min and appeared only on the die lines. Lump pick-up is not significant since it was very rare.AA6060 (0.4%Mg and 0.5%Si) alloy has about 0.27% excess silicon and therefore at 555°C, Mg2Si particles react with aluminium and excess silicon to form liquid. However normal pick-up and die line pick-up still occurred at temperatures lower and higher than 555°C and therefore it confirms that eutectic reactions do not influence formation of pick-up. Therefore die pick-up is most likely to be caused due to a mechanical process rather than a metallurgical process.