Interrelation of Solidification Processing Variables and Microstructure of a Horizontally Solidified Al-based 319.1 Alloy

Abstract

In this paper, primary (λ₁) and tertiary (λ₃) dendritic arm spacings of a ternary Al – 7wt.% Si – 3 wt.% Cu alloy casting were characterized and correlated with solidification processing variables: growth rates (V_L), cooling rates (T_C) as well as local solidification times (t_SL). Horizontal directional solidification experiments were carried out under transient heat extraction undergoing cooling rates varying from 0.9 ^oC/s to 22 ^oC/s to be associated with samples having quite different microstructural length parameters. Techniques of metallography and optical microscopy were applied in order to have λ₁ and λ₃ measured. The obtained as-cast microstructures consisted of dendritic α-Al, with Si particles in the aluminum-rich matrix as well distributed along the interdendritic regions in the eutectic mixture interlinked with θ (Al₂Cu) intermetallic phase developing the microstructure α-Al + θ + Si. The results showed that power laws – 1.1, – 0 .55 and 0.55 express the variations of both λ₁ and λ₃ with V_L, T_C and t_SL, respectively, for investigated alloy. A comparative study with the Al – 3wt.% Cu alloy from literature was also performed and the results show that the growth law of λ₁ as a function of T_C is represented, for both the investigated alloys, by the mathematical expression given by λ₁ = constant (T_C)^-0.55.

DOI: http://dx.doi.org/10.5755/j01.ms.23.2.15768