| Aluminum matrix composites (Al-MMCs) with high volume fraction reinforcements are currently considered as potential candidate materials, which becomes one of the main topics of research and development in the field of metal matrix composites. However, the poor wettability between reinforcement and filler metal leads to poor weldability of Al-MMCs, which strictly limited its engineering appliance. For investigating the possibility of joining Al-MMCs, the process of ceramic particles wetting in spreading on the surface of Al-MMCs by ultrasonic action, the interfacial bonding mechanisms between filler metal and particles, and the technologies of ultrasonic brazing to produce a particulate reinforced bond with a different volume fraction of SiC particles were investigated. Furthermore, for obtaining the mechanical property and strengthen mechanism of composite bond, the deformation and fraction characteristic of composite bond by scanning electron microscope (SEM) in situ observation were analyzed.The liquid filler metals can spread on high volume fraction Al-MMCs, however, an intimate contact between the reinforcement and the filler can't be established due to the presence of oxide films on molten alloy and a gas layer on a ceramic particle surface. Cavitations in the liquid alloy induced by ultrasonic breaking the oxide films and the gas layer, SiC particles can be satisfactory wetted by the filler. By ultrasonic assisted casting method, SiCp/Zn-Al composites were prepared. The interface is seen to be rather plannar and clean with no voids present, this means that the bonding is strong and of an electrostatic nature with no reaction mass or interdiffusion present.Based on the ultrasonic assisted wetting result, the possibility of ultrasonic assisted infiltrating of joint gap was investigated. The gas porosities and unfilled defects form in bond. The surface morphology of composite causes the formation of gas porosities, which can be eliminated by changing the surface roughness. There are lots of matrix loose zones after composite fabrication, which effect the propagation of ultrasonic in the surface of MMCs. Macroscopically disorganized capillary filling flow of liquid filler metal results in surrounding of the liquid and forms incomplete filling defect, which can be eliminated by changing the method of adding filler metal. The maximum shear strength of the joint can reach to 165 MPa.In order to obtaining structure compatibility and increasing the bond strength, the composite structure bonds were fabricated. During the brazing process, ultrasonic vibrations are applied to samples for bonding and a significant dissolution of the filler material into the matrix alloy in the base materials occurred. SiC particles in the partial melting layer of the base material are transferred into the liquid filler under ultrasonic action and a bond with homogeneously distributed reinforcements is obtained after solidification. As brazing temperatures are increased, the thickness of the dissolution layers in the base material increases. The volume fraction of SiC particles in the bonds can be varied by changing the brazing temperature. The bond strength of the reinforced bonds increases from 157 MPa to 232 MPa as the volume fraction of SiC particles ranged from 7% to 35%.The observed SEM crack paths and near-tip damaged microstructures show that the microcracks generate in eutectic phase. The transfer of load from the matrix to the reinforcing phase leads to most of particles cracking. Theα-Al phases in composite bond have an outstanding plastic deformation ability, which impedes the aggregation of microcracks and lead to a deflected crack profile. As the volume fraction of reinforcements increases, a straight crack growth path changes to a meandering crack profile, and thus a increasing of crack propagation time. Several mechanisms of strengthening have been proposed, which are considered responsible for the improved strength of composite bond: An strengthen resulting from an increase ofα-Al phases and decrease of eutectic phase in the matrix alloy; Classical strengthening through load transfer between the matrix alloy and the ceramic; Enhanced dislocation density in the matrix alloy due to the presence of particulate reinforcements.
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