Effect of Ca addition on solidification microstructure of hypoeutectic Al-Si casting alloys

Abstract

The effect of Ca addition on the solidification microstructure of hypoeutectic Al-Si casting alloys was investigated using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) methods with particular attention focused on the change of morphologies of primary α-Al and eutectic silicon. Meanwhile, solute distribution in solid-liquid was simulated according to Scheil-Gulliver law. Results showed that primary α-Al and eutectic silicon were refined as Ca content increased because of the variation of the solute concentration in liquid. The addition of Ca increased the nucleation sites like Al 3 Ti or Al 2 Cu to promote the nucleation of primary α-Al. Affected by modification effect of Ca, the shape of eutectic silicon changed from flake to fibrous structure. In addition, coarse plate Ca-rich phases could be found along the grain boundary with high Ca content.

Effect of Al2Ca Addition and Heat Treatment on the Microstructure Modification and Tensile Properties of Hypo-Eutectic Al–Mg–Si Alloys

“…Ca-induced SDAS refinement of the primary α-Al phase was also reported in previous studies [ 19 , 20 , 21 , 22 , 23 ]. Zhang [ 22 ] reported a decrease in the dendritic size of A356 alloy upon the addition of 0.06 wt% Ca.…”

“…Therefore, these white phases are believed to be Ti-based alloys with a significant amount of Ca. Moreover, Ca has a very high affinity for oxygen; therefore, the mechanism proposed by Ravi [ 24 ] and Jiao [ 23 ], which was related to improving the potency of nuclear particles in the melt, can be related to the dendritic refinement in the current study. That is, free Ca in the melt reacts to oxides present on Ti-based particles and scavenge oxygen from these particles.…”

“…It was stated that refinement was related to increased undercooling by the enrichment of Ca on the solid/liquid interface, and consequently, it restricted the growth of the primary α-Al phase. However, in another study [ 23 ], it was reported that Ca addition in inoculated Al–Si–Mg ternary alloys increases the nucleation of primary α-Al phases by promoting heterogeneous nucleation sites Al 3 Ti or Al 2 Cu, which in turn resulted in dendritic refinement. Similar to Jiao [ 23 ], Ravi [ 24 ] also suggested that the addition of elements with high oxidation tendency tends to increase the efficacy of Ti-based particles (TiAl 3 and TiB 2 ) by scavenging oxygen present on their surface and thus improves wettability as well as by reducing the agglomeration tendency of these particles.…”

“…However, in another study [ 23 ], it was reported that Ca addition in inoculated Al–Si–Mg ternary alloys increases the nucleation of primary α-Al phases by promoting heterogeneous nucleation sites Al 3 Ti or Al 2 Cu, which in turn resulted in dendritic refinement. Similar to Jiao [ 23 ], Ravi [ 24 ] also suggested that the addition of elements with high oxidation tendency tends to increase the efficacy of Ti-based particles (TiAl 3 and TiB 2 ) by scavenging oxygen present on their surface and thus improves wettability as well as by reducing the agglomeration tendency of these particles. In this study, the elemental distribution analysis was performed using SEM–EDS analysis, as shown in ( Figure 2 c) and ( Figure 3 ).…”

Wear Characteristics of Recycled Cast Al-6Si-3Cu Alloys

“…Three alloy variants containing 0.02%Ca (herein known as Ca-modified), 0.38%Fe (Fe-added) and 0.9%Fe+0.45%Mn (Fe-Mn added) were obtained by addition of respective granules and exhaustively stirred for chemistry homogenization. The addition of Ca into the alloy was meant to enhanced Si refinement as reported in literature [15], [16]. The addition of Fe and Mn influence both the microstructure and mechanical properties [17].…”