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

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