Worldwide, the use of cast aluminum for automotive components is increasing. This is driven by the industry need to meet current as well as future customer and legislative expectations (such as reduced weight and increased fuel economy) while maintaining or improving vehicle performance. Because of this, a need exists for detailed information on how the mechanical properties of aluminum alloys are affected by factors such as composition and processing. This is especially important with regard to the presence of microstructural discontinuities such as porosity, which can reduce the amount of material present that can carry an applied load. Thus, a study was conducted to compare the effect of porosity on the tensile properties of two castings; these castings were chosen such that the microstructures were equivalent except for porosity levels. The results show that tripling the average pore size yields a 19 percent decrease in the average ultimate tensile strength; a significant difference was not observed for the yield strength. The data for the elongation showed a small absolute decrease that is believed to be minor. It is concluded that large changes in pore size and in the amount of porosity had a small effect on the tensile properties. To establish an understanding of the statistics of tensile properties, a large number of samples were tested. Analysis found that a minimum of 16 samples are needed to establish a mean at a 98 percent confidence level. Further, conventional metallographic measurements were not found to accurately characterize the pore sizes that existed in the castings.
展开▼
