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 (VL), cooling rates (TC) as well as local solidification times (tSL). Horizontal directional solidification experiments were carried out under transient heat extraction undergoing cooling rates varying from 0.9 °C/s to 22 °C/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 VL, TC and tSL, 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 TC is represented, for both the investigated alloys, by the mathematical expression given by λ1 = constant (TC)-0.55.