Microstructure, Property And Strengthening Mechanism Of Aluminum Matrix Composites Synergy Reinforced By Ti Particles And SiC_p

Composites have attracted material researchers’ attention greatly because of its designable advantage over the others. Aluminum matrix composites(AMCs) have outstanding properties of high specific strength, high specific modulus, and good wear resistance so on. The improvement in the content of the high performance reinforcements in AMCs could result in a high performance AMCs with high strength and good wear resistance. However, with the minor increase in the content of the reinforcements, the strength and the ductility/toughness of the AMCs show an opposite trend between each other. In this research, hybrid metal-ceramic reinforced AMCs with certain amount and sizes of uniformly distributed toughened-metal zones in the matrix were prepared by casting processes to achieve an improved property combination of strength, ductility/toughness and reserved wear resistance.At first, composites with different matrixes(2024Al and 7075Al), different reinforcements(Ti B2, Si C and Ti) or reinforcement combinations were prepared using squeeze casting processes. Mechanical properties were studied to get an optimum tensile properties combination of matrix and reinforcement. Results shown that the fabricated 7075 Al composites synergy reinforced by Si C particles and Ti metallic particles could achieve better tensile properties. The existence of the Ti metallic particles in the composites led to a significantly improvement of strength and damage tolerance. This new material achieved an excellent tensile property combination of improved tensile strength and plasticity.Secondly, the effects of metallic Ti particles on the aging behavior of the composites were studied. The existence of the Ti metallic particles in the composites reduced the dislocation density in the matrix induced by the thermal misfit, making the nucleation of Guinier-Preston(GP) zones or intermediate phases in the matrix difficult and leading to a reduction of the activation energy for precipitates growth. The segregation of solute Mg atoms in the vicinity of the Ti particles caused a lower density of the solute atoms in the matrix and would be facilitated by the high diffusivity paths formed by the generated dislocations induced by the thermal misfit. This segregation of solute Mg atoms made the composite show different sensitivity to the aging temperature under different aging temperature ranges. Although the existence of the Ti metallic particles reduced the activation energy, the higher precipitation temperature and lower density of the solute atoms delayed the peak aging hardness of the composites. Besides, the tensile strength and the ductility of the composites were both improved after aging treated under the optimum aging conditions. The strengthened interface between the Ti particles and the matrix alloy as results of the thickened Mg-Ti diffusion layer and the formation of the Ti Al3 layer only ensured a much more effective strengthen effects of the Ti particles, resulting in the improved ductility for the aging treated composites.Thirdly,the effects of metallic Ti particles on the fracture behavior and strengthening mechanism of the composites were investigated. The damage evolutions of the composites were influenced by the size and property of the reinforcement particles. The larger Si C particles tended to crack more easily than the smaller ones during the deformation process. The breakage of the Si C particles caused inefficiency in load transfer capability and consequently degraded the mechanical properties of the composites. Meanwhile, the preferentially fractured large Si C particles accelerated the propagation of the crack and deteriorated the ductility of the composites. While, micro-zones formed by Ti particles in the center and matrix alloy with few dislocations around released stresses and deformed synergistically during deformation, which decreased the breakage of Si Cp and improved the plastic deformation ability of the matrix, resulting in a good combination of strength and ductility. In addition, Ti particles in the composites could hinder the propagation of the cracks and impart incredible improvements in the damage tolerance of the fabricated AMCs. The results obtained are beneficial in understanding the failure mechanisms and the microstructure-property relationships of composites reinforced by metal and ceramic particles synergistically, and very meaningful for the property optimization and design of composites.At last, the effects of metallic Ti particles on the friction and wear behavior of the composites were discussed. The wear behaviors of the composites were a mixed feature of fatigue wear and abrasive wear. The synergistic deformation and stress release effects of the Ti particles not only made the breakage of the Si Cp in the composites difficult which led to a decrease of the friction coefficient of the composites, but also hindered the propagation of the fatigue cracks effectively that caused an improvement of the wear resistance for the composites under low load. With the improvement of the load, the stresses between the Ti particles, Si C particles and the matrix increased sharply due to their different strain response to the load, leading to an increase of the number of the cracked Si C particles in the stress affected zone under the wear surface. This also made the propagation of the fatigue cracks in the composites become easier and degraded the wear resistance of the composites.As the researches indicated, the metal-ceramic synergy reinforced aluminum matrix composites have a unique microstructure. Thus, it derives a series of unique properties, such as light weight, high strength, plasticity, wear resistance, and other excellent properties so on. This prospective multiple/multi-scale microstructure toughened composite technology would be significant for the rapid development of metal matrix composites.