Abstract
In this paper, primary ( λ 1 ) and tertiary ( λ 3 ) 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 o C/s to 22 o 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 λ 1 and λ 3 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 (Al 2 Cu) 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 λ 1 and λ 3 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 λ 1 as a function of T C is represented, for both the investigated alloys, by the mathematical expression given by λ 1 = constant (T C ) -0.55 . DOI: http://dx.doi.org/10.5755/j01.ms.23.2.15768
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