Comparison On Microstructures And Properties Of Brake Discs Made Of Four Particle Reinforced Aluminum Alloy Matrix Composites Formed By Centrifugal Casting

In this paper,slurry preparation and forming processes of three autogenous particle reinforced hypereutectic Al-Si alloy matrix composites, which were Al-19Si-3Mg, Al-21Si-5Mg and Al-21Si-5Mg-1Cu-1Ni-0.2Ti-0.4Mn, and a SiC particle reinforced Al-Si alloy matrix composites were studied. A feasible centrifugal casting mould was designed. And the centrifugal casting process and the temperature field of aluminum alloy brake disk and the mould were simulated by using commercial software ProCAST, the result of which indicated that when the pouring temperature was more than 640℃, and the centrifugal rotational speed was 300r/min or 400r/min, a full-filled casting could be obtained. This result was valuable for designing the forming processes.Seven feasible centrifugal casting forming processes, which were pouring temperature 730℃, mould temperature 500℃, centrifugal rotational speed 800r/min (marked'a') for Al-19Si-3Mg; pouring temperature 725℃, mould temperature 300℃centrifugal rotational speed 400r/min (marked'b1') and pouring temperature 780℃, mould temperature 400℃, centrifugal rotational speed 400r/min (marked'b2') for Al-19%Si-5%Mg; pouring temperature 794℃, mould temperature 300℃, centrifugal rotational speed 400r/min (marked'c1') and pouring temperature 757℃, mould temperature 100℃, centrifugal rotational speed 400r/min (marked'c2') for Al-21Si-5Mg-1Cu-1Ni-0.2Ti-0.4Mn; pouring temperature 640℃, mould temperature 400℃centrifugal rotational speed, 400r/min (marked'd') for ZL104; pouring temperature 720℃, mould temperature 600℃, centrifugal rotational speed 800r/min (marked'e') for SiC particle reinforced Al-Si alloy matrix composites, were used to form seven brake disks successfully. Everyone of those disks were dissected into three parts, the first one of which would directly dissect again while the second one of which would be T4-heat treated, and the third one would be T6-heat treated. Then samplinged those bake disks at different radial positions, and 63 samples were obtained.After observing the microstructure, we found that the more the percentage composition of Si, the more the volume fraction of primary crystal Si particles, and that there wasn't Mg2Si particles in those samples in which the percentage composition of Mg was 3% while there were obviously in those samples in which the percentage composition of Mg was 5%. We also found that the lower the pouring temperature and mould temperature, the smaller the primary crystal Si particles; and that T4 and T6 heat treatment translated the reticular eutectic structure in the matrix into short-pole-like shape.After testing and comparing the wear-resisting property and hardness of those samples, we found that the smaller the strengthen particles and the more the volume fraction of strengthen particles, the better the wear-resisting property, and that the higher dislocation density, the higher the hardness.This research indicated that when the pouring temperature was 757℃, the mould temperature was 100℃, and the centrifugal rotational speed was 400r/min, the material Al-21Si-5Mg-1Cu-1Ni-0.2Ti-0.4Mn could get the highest hardness, which was HRB 89.6, and a good wear-resisting property, the wearing quantity of which was 16.9mg tested by the equipment for wear resisting property experiment designed by ourself after T6 heat treatment. So it was an excellent material for forming brake disk.