Magnesium alloys are widely used in engineering applications, including aerospace and automobile industries, due to their desirable properties, such as lower density, high damping capacity, relatively high thermal conductivity, good machinability, and recyclability. Researchers have, therefore, been developing new magnesium materials. However, mechanical and corrosion properties are still limiting many commercial applications of magnesium alloys. In this Ph.D. thesis research, I developed Mg-Ti composite materials to offer some solutions to further improve the mechanical behavior of magnesium, such as titanium-magnesium (Ti-Mg) claddings, Mg-Ti multilayers, and Ti particle enforced Mg alloys. Low cost manufacturing processes, such as hot roll-bonding (RB) and accumulative roll-bonding (ARB) techniques, were used to produce Mg-Ti composites and sheets. The microstructural evolution and mechanical properties of composites were investigated using optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD), nanoindentation, and tensile tests. In the first part of this study, I investigated the bonding strength of the AZ31/Ti to understand the mechanical properties of Mg/Ti composites. Using a single pass RB process, I fabricated AZ31/Ti multilayers with the thickness reduction in a range of 25% to 55%. The hot-rolled AZ31/Ti multilayers were heat-treated at 400 °C for 6, 12, and 24 hours, respectively, in an argon atmosphere. Tensile-shear tests were designed to measure the bonding strength between AZ31/Ti multilayers. Furthermore, the experimental results revealed good bonding of the AZ31/Ti multilayers without forming any intermetallic compounds in the as-rolled and heat-treated AZ31/Ti multilayers. The good bonding between Ti and AZ31 is the result of diffusion bonding whose thickness increases with increasing heat-treatment time and thickness reduction. The shear strength of the Ti/AZ31 multilayer increases with increasing bonding layer thickness. In the second part of this study, I characterized the microstructure and texture of three-layered Ti/AZ31/Ti clad sheets which were produced by single-pass hot rolling with a reduction of thickness 38% (sheet I) and 50% (sheet II). The AZ31 layer in sheets I and II exhibited shear bands and tensile twins {1012}⟨1001⟩ . The shear bands acted as local strain concentration areas which led to failure of the clad sheets with limited elongation. Heat treatment caused changes in the microstructure and mechanical properties of clad sheets due to static recrystallization (SRX) on twins and shear bands in the AZ31 layer. Recrystallized grains usually randomize the texture which causes weaken the strong deformed (0001) basal texture. Twins served as nucleation sites for grain growth during SRX. Tensile tests at room temperature showed significantly improved ductility of the clad sheets after heat treatment at 400°C for 12h. The results showed that the mechanical properties of clad sheets II are better than clad sheet I: The clad sheet II shows elongation 13% and 35% along the rolling direction (RD) for as-rolled and annealed clad sheet, respectively whereas the clad sheet I shows elongation 10% and 22% along RD for as-rolled and annealed clad sheet, respectively. In the final part of this study, I examined the effects of dispersed pure titanium particles (150 mesh) with 0, 2.3, 3.5, 4.9, and 8.6 wt. % on the microstructure and mechanical properties of AZ31-Mg alloy matrix. Mg-Ti composites were processed through three accumulative roll bonding (ARB) steps using thickness reductions of 50% in each pass followed by heat treatment at 400 °C for 12 h in an argon atmosphere. ARB is an efficient process to fabricate Mg-Ti composites. Mechanical properties of Mg- 0Ti and Mg-2.3Ti composite were enhanced by ~ 8% and 13 % in yield strength and ~ 30% and 32 % in ultimate tensile strength, respectively. Meanwhile, the elongation of the composites were decreased by 63% and 70%, respectively. After heat treatment, the results showed a decrease in yield strength and increase in elongation to fracture. The mechanical properties of the Mg-0 and Mg-2.3Ti composite were enhanced: ultimate tensile strength by 9% and 7%, and elongation by 40% and 67%, while the yield strength was decreased by 28% and 36% compared with the initial AZ31. Enhancements of strength and ductility were the results of two mechanisms: a random matrix texture by ARB and ductile titanium particle dispersion.

O presente trabalho teve como objetivo a caracterização mecânica, microestrutural e inspeção fratográfica do compósito de matriz de alumínio Al-1100 reforçado com partículas de carbeto de silício-SiC (40 μm) fabricados por meio de laminação acumulativa (ARB- do inglês Accumulative Roll Bonding), assim como, para efeito comparativo, foram estudados o Al-1100 processado por ARB sem adição de partículas e Al-1100 como recebido. Ensaio de desgaste microadesivo com esfera fixa e ensaio de tração unidirecional quase estático que foram realizados em amostras sem entalhes e em amostras contendo diferentes geometrias de entalhe. Microscopia óptica, microscopia eletrônica de varredura nos modos: elétrons secundários, elétrons retroespalhados, espectroscopia de energia dispersiva por raios-X e difração de elétrons retroespalhados, difração de raios-X e microtomografia computadorizada foram utilizados para caracterizar as amostras. Os resultados obtidos mostraram êxito da incorporação de partículas de SiC na matriz de Alumínio por meio do processo ARB. Houve ganhos relevantes na resistência máxima à tração, na rigidez e na deformação máxima no momento da ruptura, devido à incorporação de SiCp. Essas propriedades foram bastante influenciadas na presença de concentradores de tensão (entalhes). A resistência ao desgaste do compósito foi excepcionalmente incrementada comparativamente aos demais materiais. Todos os resultados foram corroborados pelas análises microetrutural e fratográficas. / The present study aims to characterize mechanical, microstructural and through fractographic inspection laminates Al-1100 aluminum matrix composite reinforced with silicon carbide particles, SiCp (40 μm), manufactured by accumulative roll bonding (ARB), as well as, for comparative effect, were studied Al-1100 processed by ARB without the addition of particles and Al-1100 received. Micro-adhesive wear test with fixed ball and test almost static unidirectional traction were performed on samples without scoring, and in samples containing different geometries notches. Optical microscopy, scanning electron microscopy modes: secondary electrons, backscattered electrons, energy dispersive X-ray and electron backscatter diffraction, X-ray diffraction and computed microtomography, these were used to characterize the samples. The results indicated successful incorporation of SiC particles in the aluminum matrix by ARB process. There have been significant gains in maximum tensile strength, stiffness and maximum deformation at the time of rupture, due to incorporation of SiCp. These properties were strongly influenced in the presence of stress concentrators (notches). The resistance of the composite wear was exceptionally increased compared to Al-1100 ARB. All results were corroborated by microstructural and fractographics analysis.

O presente trabalho teve como objetivo a caracterização mecânica, microestrutural e inspeção fratográfica do compósito de matriz de alumínio Al-1100 reforçado com partículas de carbeto de silício-SiC (40 μm) fabricados por meio de laminação acumulativa (ARB- do inglês Accumulative Roll Bonding), assim como, para efeito comparativo, foram estudados o Al-1100 processado por ARB sem adição de partículas e Al-1100 como recebido. Ensaio de desgaste microadesivo com esfera fixa e ensaio de tração unidirecional quase estático que foram realizados em amostras sem entalhes e em amostras contendo diferentes geometrias de entalhe. Microscopia óptica, microscopia eletrônica de varredura nos modos: elétrons secundários, elétrons retroespalhados, espectroscopia de energia dispersiva por raios-X e difração de elétrons retroespalhados, difração de raios-X e microtomografia computadorizada foram utilizados para caracterizar as amostras. Os resultados obtidos mostraram êxito da incorporação de partículas de SiC na matriz de Alumínio por meio do processo ARB. Houve ganhos relevantes na resistência máxima à tração, na rigidez e na deformação máxima no momento da ruptura, devido à incorporação de SiCp. Essas propriedades foram bastante influenciadas na presença de concentradores de tensão (entalhes). A resistência ao desgaste do compósito foi excepcionalmente incrementada comparativamente aos demais materiais. Todos os resultados foram corroborados pelas análises microetrutural e fratográficas. / The present study aims to characterize mechanical, microstructural and through fractographic inspection laminates Al-1100 aluminum matrix composite reinforced with silicon carbide particles, SiCp (40 μm), manufactured by accumulative roll bonding (ARB), as well as, for comparative effect, were studied Al-1100 processed by ARB without the addition of particles and Al-1100 received. Micro-adhesive wear test with fixed ball and test almost static unidirectional traction were performed on samples without scoring, and in samples containing different geometries notches. Optical microscopy, scanning electron microscopy modes: secondary electrons, backscattered electrons, energy dispersive X-ray and electron backscatter diffraction, X-ray diffraction and computed microtomography, these were used to characterize the samples. The results indicated successful incorporation of SiC particles in the aluminum matrix by ARB process. There have been significant gains in maximum tensile strength, stiffness and maximum deformation at the time of rupture, due to incorporation of SiCp. These properties were strongly influenced in the presence of stress concentrators (notches). The resistance of the composite wear was exceptionally increased compared to Al-1100 ARB. All results were corroborated by microstructural and fractographics analysis.