The plane-to-cellular-to-dendrite transition of the shape of the crystallization front during the crystallization of Al-Cu alloys

The evolution of the crystallization front from a planar to a dendritic one as a function of the G L/(Rc 0) parameter was investigated during the crystallization of Al-Cu alloys by the vertical Bridgman method. Six series of alloys with different initial compositions of Cu were solidified at different growth rates. A mathematical model for the heat transfer during vertical Bridgmen crystal growth was developed. The model was solved using the finite element method. The temperature gradient in the melt at the beginning of crystal growth was calculated using the obtained model. Discrete stages of the crystallization front were identified in the experiments, as the ratio G L/(Rc 0) decreased. U okviru ovog rada ispitivana je transformacija fronta kristalizacije od ravnog ka dendritnoj strukturi kao funkcija parametra GL/(Rc0) pri kristalizaciji legure Al-Cu metodom vertikalni Bridgman. U tom cilju izvedeni su eksperimenti sa sest serija uzoraka razlicitih pocetnih koncentracija i razlicitim brzinama rasta. Izveden je i matematicki model procesa rasta kristala metodom vertikalni Bridgman koriscenjem metode konacnih elemenata. Na osnovu matematickog modela izracunat je temperaturni gradijent u rastopu u trenutku kada zapocinje rast kristala. U okviru eksperimentalnog opsega sa snizenjem vrednosti parametra GL/(Rc0) dolazi do postepenog razvoja fronta kristalizacije po etapama.