Papers by Author: K. Sadayappan

Abstract: Magnesium automotive components are currently produced by high pressure die casting. These castings cannot be heat-treated to improve the strength and ductility mainly due to the casting imperfections such as porosity and inclusions created by the air entrainment during the turbulent mold filing. These imperfections also prevent magnesium components to be used for highly stressed body components. Efforts were made to produce high integrity magnesium castings through a Super-Vacuum Die Casting process. The AZ91D castings were found to have very low porosity and can be heat-treated without blisters. The tensile properties of the castings were satisfactory. The mechanical properties and thermal analysis indicate that the conventional heat treatment procedure needs to be optimized for such thin sectioned and rapidly solidified castings which have very fine microstructures.

Abstract: The mechanisms of hot tearing are generally understood; inadequate feeding initiates the tear and further thermal deformation propagates the tear. However, a reliable experimental methodology/apparatus to quantitatively measure and characterize hot tearing is not available for the casting industry. In this study, a hot tearing apparatus with a load cell and LVDT developed at CANMET-MTL was used to measure the load and contraction in the mushy zone of an Al-Cu alloy. The onset of hot tearing can be determined from the load curve, its first derivative and cooling curve. The linear solidification contraction of the bar is measured. Alloy 206, which is an alloy that is quite prone to hot tearing was evaluated by the apparatus; results are given and discussed.