Influences of the Process Defect on the Material Properties of a Thin-Walled Cast Structure.

摘要

The magnesium high pressure die casting process is widely reported as producing parts that exhibit large local variation in part properties. Inherent defects associated with the process are reported to be the primary reason for such variations in properties. The Pore band defect, which is caused by micro shrinkage pores, was observed to be a common defect in thin walled magnesium die cast components. It divides the cast wall into three layers and eventually produces a composite laminate structure within the thickness. Based on the thickness and microstructure features of each layer, the bulk mechanical property varies. In order to better understand this phenomenon, test samples were prepared and the wall thickness was reduced by machining, step by step, while measuring the bulk porosity in every step. Standard tensile sub size samples were sliced into three layers and each layer was tested under uni-axial tensile loading conditions. This paper presents variations in mechanical properties through the thickness direction that was observed experimentally. Further, an analytical model was developed and tested to approximate the failure strain based on the pore band characteristics.