The Effect of the Holding Time on the Microstructure of Gd-Containing AlSi7Mg Alloys

Among lanthanides, Gd addition has been expected to show a good achievement in changing the microstructure of the alloys for better performance in high-temperature applications. Nevertheless, there is a lack of information about the casting practice of Gd addition in terms of holding time and fading effect. In this study, the effective holding time and the fading effect of Gd in AlSi7Mg alloy have been investigated. After minor (0.1 wt. %) and major (0.5 wt. %) Gd additions, different holding times in the range from 15 to 200 min were examined. The chemical composition of the molten bath was frequently verified as a function of the holding time. Thermal analysis macro- and microstructural investigations were performed. The results indicate that 45 min of holding time can produce eutectic Si refinement. Longer holding times promote Gd settling leading to grain coarsening and formation of larger eutectic Si flakes.