The coupled zone of rapidly solidified AlSi alloys in laser treatment

Abstract

Laser-melted tracks were produced on AlSi samples containing between 15.5 and 26 wt% Si with the resultant solidification rates being measured by taking a longitudinal section through the centre of the laser trace. The Al-rich boundary of the coupled zone, i.e.the growth rate-concentration limit at which the transition from fibrous AlSi eutectic to α-Al dendrites plus interdendritic eutectic takes place, has been experimentally determined for concentrations of Si varying from 15.5 to 20 wt%. Supposing that the growing structure, for a given growth rate, is the one having the higher growth temperature, good agreement is found with the more recent microstructural growth models when kinetic effects are taken into account. For concentrations of Si higher than 20 wt%, primary Si crystals imbedded in equiaxed eutectic grains are observed which replace columnar eutectic and dendritic growth.