The Research On Organization And Performance Of Aluminium Matrix Composites By Friction Stir Processing

Friction Stir Processing(FSP)is a new metal solid proeessing technology Developed by Mishra the university of Missouri on the basis of the development of friction stir welding. In the present dissertation, SiC particles reinforced cast aluminum alloy ZL101matrix composites were fabricated by friction stir processing(FSP). The effects of rotation speed, advancing speed, the grooves of workpiece and passes of friction stir processing on SiC particles distribution and the influence of the microstructure, it summarizes the characteristics of SiC particle distribution and processing zone of processed alloy. The effect of preparation technology parameters on the hardness and tensile strength of composites were investigated on this basis by means of testing the mechanical properties of composites fabricated by friction stir processing. The fracture mechanism of composites were studied by comprehensive analyzing microstructure and fracture morphology of composites via SEM. Main study results are as follows:SiC particles reinforced aluminum alloy matrix composites were successfully fabricated by Friction stir Processing. Under this experimental condition, SiC particles of the composite layer were uniformly distributed in the base metal and good forming after4-passes of friction stir processing at the parameters with rotation speed of800r/min and advancing speed of50mm/min. The microhardness increased and tensile strength decreased of composites materials after4-passes of friction stir processing. The average micro-hardness of friction stir zone was68HV, which was as1.5times much as the base metal hardness (45HV). Tensile strength decreased to176Mpa, which was81%of the base metal.To improve the rotation rate and advancing speed is favourable toward reducing SiC particles of the composites materials with with swirl and banded together and promoting the uniformity of processing organization. The stir tool rotating speed is too large will cause the grain growth of the processing zone and advancing speed too large will cause the processing zone of loose organization. As the rotation rate and tool processing speed increased, the micro-hardness and tensile strength of the composites decreased. The SiC particles distributed uniformly in the center of friction stir zone can be easy to obtain when the depth is too shallow and the width is too narrow of the grooving. But, there is little SiC particles distributed in the other zones, such as shoulder of friction stir zone and edge of friction stir zone. Moreover,, the overall micro-hardness can be improved as the increasing of the depth and width of the grooving, but the too depth and the too width of the grooving tends to cause the SiC particles clustering in the center of friction stir zone.The increase of processing passes makes the SiC particles clustering transition from approximated swirl to banded in the processing texture, showing the linear transition and the dispersion characteristics. After four-passes of friction stir processing, the microstructure of the processing zone has made a remarkable improvement in uniformity. The more the processing times, the more the micro-hardness and strength of the composites, and the fluctuation of the micro-hardness value decreases.The fracture of one-pass friction stir processing tensile specimen adding SiC particles is mixed fracture, brittle fracture is obvious. The fracture of four-passes FSP composites tensile specimen is characterized by dimples, the overall performance exhibited ductile fracture. Fracture of the composites materials presents the characteristics of ductile fracture, the fracture mechanism include ductile fracture and tear of the combination of SiC particles and matrix interface.