Mechanisms of formation of pyrolysis defects in aluminum lost foam castings

摘要

This paper presents experimental observations related to the formation of pyrolysis defects and presents possible mechanisms for their formation. The classification of these defects using metallography, surface composition and surface topography helps to explain the formation of folds and blisters. Auger analysis of pyrolysis defects showed an oxide and carbon layer. The oxide layer contained aluminum and, for some alloys, magnesium. Photomicrographs showed a eutectic that formed around the fold and blister defects with varying degrees of modification. SEM images showed evidence of turbulent metal flow and porosity in blisters, which were not present in fold defects. Defect maps showed that the blisters are concentrated in the middle of the flange, while folds are located at the end of the flange, particularly where the two metal streams meet. Based on these and other observations, theories on the mechanisms by which folds and blisters form are presented.