Theoretical density determination for secondary al alloys

摘要

The deleterious effects of dispersed porosity or microporosity in cast aluminum alloys are widely recognized. Ductility and fatigue resistance, in particular, are strongly affected. In the course of investigating improvements in casting techniques, it is often necessary to determine the levels and distribution of porosity, as well as its shape and size, within a particular casting. While the porosity level can be evaluated using pyknometry or image analysis techniques, pyknometry techniques are much less time consuming and less expensive than image analysis techniques and are much less affected by the randomness of the porosity location in the sample. In evaluating the porosity using pyknometry, a theoretical density of the alloy must be used. This theoretical density is usually obtained from reference materials, but because of the multiple casting processes experienced by secondary aluminum alloys, their chemical compositions and theoretical densities vary greatly. Th is paper presents a method for determining the theoretical density of an engineering alloy using the combination of pyknometry and image analysis techniques. This method can be used to decrease casting evaluation time by analyzing the porosity of one specimen from a casting using image analysis extensively, then using the results to evaluate the rest of the casting specimens using pyknometry. The new method is currently being employed in an investigation of pressurized riser-based feeding supported by the U.S. Dept. of Energy (USDOE) through the Cast Metals Consortium (CMC) and guided by the AFS 2-H Committee.