Metallurgical and Materials Transactions A

, Volume 43, Issue 12, pp 4846-4858

Feeding and Distribution of Porosity in Cast Al-Si Alloys as Function of Alloy Composition and Modification

  • Niels Skat TiedjeAffiliated withDepartment of Mechanical Engineering, Technical University of Denmark (DTU) Email author 
  • , John A. TaylorAffiliated withCAST Co-operative Research Center, School of Mechanical & Mining Engineering, The University of Queensland
  • , Mark A. EastonAffiliated withDepartment of Materials Engineering, CAST Co-operative Research Centre, Monash University

Rent the article at a discount

Rent now

* Final gross prices may vary according to local VAT.

Get Access


Unmodified, Na-modified, and Sr-modified castings of Al-7 pct Si and Al-12.5 pct Si alloys were cast in molds in which it was possible to create different cooling conditions. It is shown how solidification influences the distribution of porosity at the surface and the center of the castings as a function of modification and Si content in sand- and chill-cast samples. Eutectic modification, Si content, and cooling conditions have a great impact on the distribution of porosity. Unmodified and Na-modified castings are more easily fed with porosity tending to congregate near the centerline of the casting, while Sr-modified castings solidify in a mushy manner that creates a more homogeneous distribution of porosity in the casting. The amount of porosity was highest in the Sr-modified alloys, lower in the Na-modified alloys, and lowest in the unmodified alloys. The size of the porosity-free layer and the effectiveness of the feeders were greater in the castings made with the steel chills due to the increased thermal gradients and consequent increase in the directionality of solidification.