Abstract:Two kinds of Al based functionally gradient composite tubes reinforced by primary Si particles alone and primary Si/ in situ Mg₂Si particles jointly were successfully prepared by centrifugal casting, and their structural and mechanical characters were compared. It is found that the composite reinforced with primary Si particles takes a characteristic of particles distribution both in the inner and outer layers. However, composite reinforced with primary Si/Mg₂Si particles jointly takes a characteristic of particles distribution only in the inner layer and shows a sudden change of particles distribution across the section of inner and outer layers. The hardness and wear resistance of Al-19Si-5Mg tube in the inner layer are greatly higher than that in the other layers of Al-19Si-5Mg tube and Al-19Si tube. Theoretical analysis reveals that the existence of Mg₂Si particles is the key factor to form this sudden change of gradient distribution of two kinds of particles. Because Mg₂Si particles with a lower density have a higher centripetal moving velocity than primary Si particles, in a field of centrifugal force, they would collide with primary Si particles and then impel the later to move together forward to the inner layer of the tube.

Key words: centrifugal casting; functionally gradient composites; in situ primary Si particles; in situ Mg₂Si particles