The Formation Process of the Secondary Arms in the Dendritic Growth of Al-4.8 wt%Cu Alloys

Abstract

The influence of solidification conditions on the secondary arm spacing (λ_s), the angle (θ) between the primary and the secondary arms and the initial position (λ₀) of the branching of the secondary arms from a primary arm was investigated by quenching the unidirectionally solidifying Al-4.8 wt%Cu alloys. The spacing λ_s was approximately represented by the relation λ_s=const.×(the time spent from the passage of the solid-liquid interface prior to quench)ⁿ, and the constant n was approximately 1/3 in the range of experimental conditions used in the present work. The secondary arms initiated at an acute angle to the growth direction of the primary arms, and the variation of the angle θ may be an important factor for the coarsening process of the secondary arms. The initial position λ₀ was the same order as the radius of curvature at the dendrite tip.