The Researches Of Producing Process Of Semi-solid Hypereutectic Al-Si Alloy Slurry

This thesis studied the effect of cooling rate and the stirring intensity on the equivalent diameter and the aggregation of the primary Si particles during the producing of the semi-solid slurry by electromagnetic stir, so offered foundation for producing largely the hypereutectic Al-Si alloy semi-solid slurry.The cooling rate and the stirring intensity were found influencing greatly quality of semi-solid slurry during the producing the slurry of binary and multi-elements hypereutectic Al-Si alloys. The results of the thesis show:For binary hypereutectic Al-Si alloy, the cooling rate and the stirring intensity have effects on the structure of primary Si particles. There is a best cooling rate, 12°C/min, at which the minimum equivalent diameter (56.2∝m) of primary Si particles can be attained when the stirring current is 20A. When the cooling rate is lower to 12°C/min, the primary Si can be gradually refined with the increase of the cooling rate, and when the cooling rate is larger than 12°C/min, the primary Si become increasingly coarse with the increase of the cooling rate.With increasing of the stirring current under one certain cooling rate, the aggregation of primary Si particles becomes increasingly obvious and the equivalent diameter becomes increasingly large, reaches 41.9am when the stirring current is 8A and the cooling rate is 8°C/min.For multi-elements hypereutectic Al-Si alloy, the cooling rate and the stirring intensity have same effects on the primary Si. The best cooling rate is 15°C/min, when the stirring current is 22A, at which the minimum equivalent diameter reaches 32.0am. The stirring current is 8A at which the aggregation of primary Si disappears, and the equivalent diameter reaches 44.8∝m when the cooling rate is 8°C/min.Based on the researches about of effect of cooling rate and stirring intensity on the primary particles, this thesis bring up the mechanism of the primary Si particles nucleation, movement and aggregation: 1. the primary Si particles nucleate on crucible surface;2. theprimary particles move toward to middle of crucible;3.the primary particles aggregate at the middle;4. because the density of the primary is small, primary Si particles aggregated float toward the surface of the semi-solid slurry.This thesis explained the effects of cooling rate and stirring intensity on the primary Si particles by the mechanism which can instruct producing the semi-solid hypereutectic Al-Si alloy slurry.