THE DEVELOPMENT OF NUCLEATION CONTROLLED MICROSTRUCTURES DURING LASER TREATMENT OF Al-Si ALLOYS

摘要

Solidification of laser-remelted A1-26 wt/100 Si alloys has revealed a transition from constrained growth to nucleation control of microstructural evolution. Laser scanning velocities between 5 and 8 mm/s resulted in a fibrous eutectic microstructure. For scanning velocities above 8 mm/s, the microstructure consisted of equiaxed, micron-sized silicon crystals surrounded byα-Al cells that, in turn, were surrounded by fibrous eutectic. An analysis of the transition from growth-controlled to nucleation-controlled microstructure development has been formulated based upon the limiting solidification interface tempera- ture at the transition and a heterogeneous volume nucleation model.