Submitted by Caroline Xavier (caroline.xavier@pucrs.br) on 2017-08-08T13:47:52Z No. of bitstreams: 1 TES_ALBINO_MOURA_GUTERRES_COMPLETO.pdf: 7255952 bytes, checksum: 781408c060e8988a1e9c63e9d2d0855b (MD5) / Made available in DSpace on 2017-08-08T13:47:52Z (GMT). No. of bitstreams: 1 TES_ALBINO_MOURA_GUTERRES_COMPLETO.pdf: 7255952 bytes, checksum: 781408c060e8988a1e9c63e9d2d0855b (MD5) Previous issue date: 2017-07-04 / The overall objective of this work is to analyze the influence of Si and Mg contents, the percentage of porosity and the effects of hardening precipitation heat treatment on the mechanical properties of Al-Si-Mg alloys. Two alloys: Al-3,8%Si-0,25%Mg (Alloy I) and Al-6,5%Si-0,6%Mg (Alloy II) were prepared and characterized by thermal analysis and optical emission spectroscopy. After that, the alloys were solidified in a metallic mold, with and without degasification. Transversal samples were extracted from solidified ingots to analyze the as-cast structures and mechanical properties (tensile and hardness tests). Part of ingots were submitted to hardening precipitation heat thermal treatments by solutioning at 540?C for 6 hours and artificial aging at 180?C for 4 hours. After the solidification structure analysis in the Alloys I and II in samples along the ingot, it was observed that the grain medium size and the secondary dendrite arm spacing presented small variations that do not influence the variations on the mechanical properties. Regarding porosity, it was noted that Alloy II, which contains a higher content of Si and Fe, presented higher porosity percentage when compared to Alloy I. The degasification process decreased at about 50% porosity volumetric percentage. During the analysis of the mechanical properties of the alloys in the states of crude solidification, it was observed that the samples referring to Alloy II, in the degassed condition, presented higher limits of tensile strength and hardness, 175,5 MPa and 70,7 HB, respectively . Due mainly to the higher content of Si found in alloy II. In relation to the ductility, the Alloy I, in the degassed condition, presented the highest percentage of specific deformation (greater deformation ? = 1.82%), due to the lower percentage of porosity and lower content of Si and Fe. With the treatment (T6), a significant increase in the properties of both alloys can be observed. Alloy II showed the best results with thermal treatment, generating an increase of: 25% in tensile strength, 57% in deformation and 23% in hardness of the samples analyzed. Thus, alloy II, due to the higher percentage of Mg, responded better to the heat treatment. For the analysis of the correlation of the chemical composition, the percentage of porosity and the effects of the thermal treatments with the variation in the mechanical properties, mathematical models were developed that allow to predict the limit of tensile strength, deformation and hardness in Al-Si-Mg. In the analysis of the mathematical models, it was possible to identify the negative effect of the iron and porosity percentages on tensile strength and specific deformation. The increase of silicon and magnesium contents and the application of T6 contributed to higher tensile strength, specific deformation and hardness as well. / O objetivo geral desse estudo foi correlacionar ? composi??o qu?mica, a porosidade e os efeitos dos tratamentos t?rmicos de endurecimento por precipita??o em algumas propriedades mec?nicas em ligas de Al-Si-Mg fundidas. Duas ligas Al-3,8%Si-0,25%Mg (Liga I) e Al-6,5%Si-0,6%Mg (Liga II) foram preparadas e caracterizadas por an?lise t?rmica e espectroscopia de emiss?o ?ptica. Ap?s, foram solidificadas em molde met?lico, com e sem desgaseifica??o. Amostras transversais foram extra?das ao longo do comprimento dos lingotes para an?lises da estrutura de solidifica??o e determina??o das propriedades mec?nicas (ensaios de tra??o e dureza). Parte dos lingotes foram submetidos a tratamentos t?rmicos de endurecimento por precipita??o, com solubiliza??o a temperatura de 540oC por 6 horas, e posterior envelhecimento artificial a temperatura de 180?C por 4 horas. Ap?s as an?lises da estrutura de solidifica??o das Ligas I e II, observou-se que os tamanhos m?dios de gr?o e os espa?amentos dos bra?os dendr?ticos secund?rios apresentaram pequenas varia??es que n?o influenciaram nas varia??es das propriedades mec?nicas. Em rela??o ? porosidade, observou-se que a Liga II, por ter mais Si e Fe na sua composi??o, apresentou maior percentual de porosidade do que a Liga I. O processo de desgaseifica??o reduziu em aproximadamente 50% a porosidade em ambas as ligas. Durante a an?lise das propriedades mec?nicas das ligas nos estados bruto de solidifica??o, observou-se que as amostras referentes ? Liga II, na condi??o desgaseificada, apresentaram maiores limites de resist?ncia ? tra??o e dureza, 175,5 MPa e 70,7 HB, respectivamente, devido principalmente ao maior teor de Si encontrado na Liga II. A Liga I, na condi??o desgaseificada apresentou os maiores percentuais de deforma??o espec?fica (? = 1,82%), devido ao menor percentual de porosidade e menores teores de Si e Fe. Com a aplica??o do tratamento t?rmico (T6), pode-se observar um aumento significativo nas propriedades mec?nicas. Na Liga II, observou-se os melhores resultados com tratamento t?rmico, gerando aumento de: 25% na resist?ncia ? tra??o, 57% na deforma??o e 23% na dureza. Dessa forma, a Liga II por apresentar maior percentual de Mg respondeu melhor ao tratamento t?rmico. Na an?lise da correla??o da composi??o qu?mica, o percentual de porosidade e os efeitos dos tratamentos t?rmicos com a varia??o nas propriedades mec?nicas desenvolveu-se modelos matem?ticos que permitem prever o limite de resist?ncia ? tra??o, deforma??o e dureza em ligas de Al-Si-Mg. Analisando os modelos matem?ticos, identificou-se o efeito negativo do percentual de ferro e porosidade no limite de resist?ncia ? tra??o e deforma??o espec?fica, j? o aumento do teor de sil?cio, de magn?sio e aplica??o do tratamento t?rmico T6 contribu?ram para maiores limites de resist?ncia ? tra??o, percentuais de deforma??o e dureza.

Estágio realizado na empresa Traterme Tratamentos Térmicos, Lda. - e orientado pelo Eng. J. Alexandre Silva / Tese de mestrado integrado. Engenharia Metalúrgica e de Materiais. Faculdade de Engenharia. Universidade do Porto. 2012

Tese de mestrado. Mestrado Integrado em Engenharia Metalúrgica e de Materiais. Faculdade de Engenharia. Universidade do Porto. 2012

The physical properties of polymer quench bath directly affect the cooling rate of a quenched part. These properties include the type of quenchant, its temperature, concentration, and agitation level. These parameters must be controlled to optimize the quenching process in terms of alloy microstructure, properties and performance. Statistically designed experiments have been performed to investigate the effects of the process parameters (i.e. polymer concentration and agitation) on the heat transfer behavior of cast aluminum alloy A356 in aqueous solution of Aqua-Quench 260 using the CHTE quenching-agitation system. The experiments were designed using Taguchi technique and the experimental results were analyzed with Analysis of Variance (ANOVA) based on the average cooling rate. It is found that average cooling rate dramatically decreases with the increase in polymer concentration. Agitation only enhances the average cooling rate at low and medium concentration levels. From ANOVA analysis, the process parameter that affects the variation of average cooling rate most is the polymer concentration, its percentage contribution is 97%. The effects from agitation and the interaction between polymer concentration and tank agitation are insignificant. The mechanical properties of age-hardenable Al-Si-Mg alloys depend on the rate at which the alloy is cooled after the solutionizing heat treatment. A model based on the transformation kinetics is needed for the design engineer to quantify the effects of quenching rates on the as-aged properties. Quench Factor analysis was developed by Staley to describe the relationship between the cooling rate and the mechanical properties of an age-hardenable alloy. This method has been previously used to successfully predict yield strength, hardness of wrought aluminum alloys. However, the Quench Factor data for aluminum castings are still rare in the literature. In this study, the Jominy End Quench method was used to experimentally collect the time-temperature and hardness data as the inputs for Quench Factor modeling. Multiple linear regression analysis was performed on the experimental data to estimate the kinetic parameters during quenching. Time-Temperature-Property curves of cast aluminum alloy A356 were generated using the estimated kinetic parameters. Experimental verification was performed on a L5 lost foam cast engine head. The predicted hardness agreed well with that experimentally measured.

Conventional casting alloys Al-7Si-Mg A356/7 contain between 6.5 and 7.5% Si, together with 0.25-0.7% Mg and are used for critical castings in the automotive and aerospace industries. These alloys are also the most popular alloys used for semi-solid metal (SSM) forming due to good castability and fluidity imparted by the large volumes of the Al-Si eutectic. Despite their industrial importance, there is a lack of detailed research work revealing precipitate micro- and nanostructural evolution during aging of these alloys compared with the Al-Mg-Si 6000 series wrought alloys. This study characterises the heat treatment response of SSM-processed Al-7Si-Mg alloys in comparison with conventionally liquid cast alloys (investment casting and gravity die casting). It is shown that, provided that the maximum quantity of the alloy’s Mg is placed into solid solution during solution treatment, and that the alloy’s Fe content is within specification, the response to age hardening of Al-7Si-Mg alloys is independent of the processing technique used. The nanostructural evolution of Al- 7Si-Mg alloys after artificial aging with and without natural pre-aging has been characterized using transmission electron microscopy and atom probe tomography and correlated with hardness and mechanical tensile properties. The number densities and Mg:Si ratios of solute clusters, GP zones and β"-needles were determined. The heat treatment response of SSM-processed casting alloys A356/7 alloys are also compared with SSM-processed Al-Mg-Si 6000 series wrought alloys, with the advantage of having similar globular microstructures. The high Si-content of the casting alloys compared to the wrought alloys offers several advantages, including a faster artificial aging response (shorter T6 aging cycles), higher strength for comparable Mg contents and less sensitivity to prior natural aging on peak strength. Finally, an age-hardening model was developed for the Al-7Si-Mg alloys, including a method of incorporating the effects of changes in Mg-content on the aging curves. / Thesis (PhD(Eng))--University of Pretoria, 2011. / Materials Science and Metallurgical Engineering / unrestricted

The aim of this work was to improve the heat capacity estimation of a material for usage within a CALPHAD-type assessment. An algorithm is derived that estimates the trend of heat capacity with temperature based on zero Kelvin properties and the thermal expansion coefficient at the Debye temperature. The algorithm predicts not only the trend of heat capacity but also the temperature trend of the volume and the bulk modulus, which can be also included in new thermodynamic databases. The algorithm is used to assess thermophysical properties of the intermetallic phases eta (Fe2Al5), epsilon~(Fe5Al8) and tau4 (FeAl3Si2). The heat capacity of the intermetallic phases zeta, eta, theta and epsilon of the Al-Fe system and of tau4 of the Al-Fe-Si system was measured using DSC. For the phases zeta, eta, and theta, a non-linearly increasing heat capacity approaching the melting temperature was observed. In addition, the heat capacity of three bcc-based Al-Fe samples including the B2-->A2 transition were determined. The Al-rich section of the Al-Fe phase diagram was studied using DTA and quenching experiments. The homogeneity ranges of the intermetallic phases were determined using SEM/WDS measurements. Based on own and literature values, a thermodynamic description of the Al-Fe system was assessed including the modelling of A2/B2 ordering and the homogeneity range of all intermetallic phases. In addition, thermodynamic parameters of the Al-Fe-Si, Al-Fe-Mg, and the Fe-Mg-Si system were assessed to obtain a thermodynamic description of the Al-rich side of the Al-Fe-Si-Mg system, which can be used to study phase transitions of typical A356-aluminium alloys.

Aluminum alloys are of great importance in the automotive and truck industries due to the weight savings that they can help to achieve. However, the use of such alloys in applications where they are subjected to alternating stresses requires knowledge about their fatigue behavior. Moreover, extrusion induces a strong texture and microstructural heterogeneity in the material and gives a surface with long grooves parallel to the extrusion direction (ED), so-called die lines. This anisotropy in surface conditions and microstructure may affect the fatigue properties. To investigate how die lines and microstructure affects fatigue in aluminum, the high cycle fatigue properties cycles of three peak-aged AlMgSi alloys were evaluated. Flat profiles of 6060-T6, 6063-T6 and 6082-T6 were tested in uniaxial stress (R = 0.1) in a servo-hydraulic fatigue testing machine with a constant stress amplitude. Two specimen types were tested for 6063 and 6082: one with the ED parallel to the loading direction (longitudinal), and one with the ED perpendicular to it (transverse). It was found that both 6063 and 6082 displayed anisotropy in fatigue lives, with the longitudinal orientation performing better. The anisotropy was far stronger in 6082 than in 6063. Furthermore, 6060 longitudinal displayed higher fatigue strength than 6063 longitudinal at higher stress amplitudes, but lower fatigue strength at lower amplitudes. Metallographic investigations with SEM indicated that grain boundaries of the surface-layer grains were involved in the initiation of the fatigue crack. Intergranular crack propagation and separation was observed on the fracture surfaces, especially in the surface layer. The extruded surfaces also showed evidence of intergranular crack propagation. The exact sites of crack initiation could not be found so it could not be proven conclusively that die lines were sites of crack initiation in transverse specimens, but there were some indications from metallographic and macrofractographic investigations that this was the case. / Aluminiumlegeringar används mycket i bilindustrin på grund av de viktbesparingar som kan åstadkommas. Användandet av sådana legeringar i tillämpningar där det utsätts för cykliska laster kräver dock kunskap om deras utmattningsbeteende. Dessutom skapar extrusionsprocessen en stark textur och heterogenitet i mikrostrukturen och resulterar i en yta med fina fåror parallella med pressriktningen, s.k. die lines. Anisotropin i ytbeskaffningen och mikrostrukturen kan påverka utmattningshållfastheten. För att undersöka hur die lines och mikrostruktur påverkar utmattningen i aluminium testades högcykelutmattningsegenskaperna hos tre toppåldrade AlMgSi legeringar. Platta profiler av 6060-T6, 6063-T6 och 6082-T6 testades i enaxlig dragspänning (R = 0.1) i en servohydraulisk utmattningsmaskin med konstant lastamplitud. Två sorters provstavar testade av 6082 och 6063: en med pressriktningen parallell med lastriktningen (längsriktning) och en med pressriktningen vinkelrät mot lastriktningen (tvärriktning). Både 6063 och 6082 uppvisade olika utmattningsliv beroende på pressriktningens orientering mot lastriktningen, där längsriktningen hade längre utmattningsliv för båda legeringarna. Anisotropin var mycket starkare in 6082 än 6063. Dessutom uppvisade 6060 i längsriktningen högre utmattningsstyrka än 6063 vid höga lastamplituder, men lägre utmattningsstyrka vid lägre lastamplituder. Metallografiska undersökningar med SEM indikerade att korngränser i ytlagret var involverade i sprickinitieringen. Spricktillväxt i och separation av korngränser observerades på brottytorna, speciellt i ytlagret. Den extruderade ytan visade också bevis för interkristallin spricktillväxt. De exakta platserna för sprickinitering kunde inte hittas så det kunde inte entydigt bevisas att sprickinitieringen skedde i die lines i provstavar med pressriktningen vinkelrät mot lastriktningen, men i metallografiska och fraktografiska undersökningar fanns vissa indikationer att så var fallet.

Due to the increasing use of cyclically loaded cast aluminum components in automotive and aerospace applications, fatigue and fatigue crack growth characteristics of aluminum castings are of great interest. Despite the extensive research efforts dedicated to this topic, a fundamental, mechanistic understanding of these alloys' behavior when subjected to dynamic loading is still lacking. This fundamental research investigated the mechanisms active at the microstructure level during dynamic loading and failure of conventionally cast and SSM Al-Si-Mg alloys. Five model alloys were cast to isolate the individual contribution of constituent phases on fatigue resistance. The major constituent phases, alpha-Al dendrites, Al/Si eutectic phase, and Mg-Si strengthening precipitates were mechanistically investigated to relate microstructure to near-threshold crack growth (Delta Kth) and crack propagation regimes (Regions II and III) for alloys of different Si composition/morphology, grain size, secondary dendrite arm spacing, heat treatment. A procedure to evaluate the actual fracture toughness from fatigue crack growth data was successfully developed based on a complex Elastic-Plastic-Fracture-Mechanics (EPFM/J-integral) approach. Residual stress-microstructure interactions, commonly overlooked by researches in the field, were also comprehensively defined and accounted for both experimentally and mathematically, and future revisions of ASTM E647 are expected.