Effect of Casting Processes, Rare Earth Metals, and Sr Addition on Porosity Formation in Al-Si Cast Alloys

Abstract

The present work was carried out on A413.1cast alloy that was characterized by short freezing temperature range. Measured amounts of high purity (99.99%) rare earth metals (Ce, La, La + Ce) were added to the non-modified and Sr-modified molten metal. Three casting molds were used viz., graphite mold heated at 600°C for the purpose of obtaining solidification curves, metallic mold with three variable opening angles heated at 350°C, and a step-like metallic mold heated at 200 and 400°C. The main results are earth metals (RE) would lead to porosity formation in all molds with increase in its percentage in Sr-modified alloys. Since the maximum α-Al network formation temperature is in the range of 575–580°C, some of the RE may precipitate in the liquid state leading to blocking the flow of the liquid metal. However, considering the metal was degassed using high purity argon gas, most of the observed porosities are of shrinkage type. In addition, increasing the amount of used RE, and hence percentage of unsoluble intermetallics results in marked decrease in the alloy strength. The only observed advantage is the effectiveness of La is reducing the alloy grain size due to its low affinity to react with Ti.