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.