Quantitative Evaluation of Porosity in Aluminum Die Castings by Fractal Analysis of Perimeter

In the die-casting process, the formation of pores in components is unavoidable. This porosity has a harmful effect on the strength and pressure tightness of die castings. To eliminate the porosity in components, its predominant cause has to be identified as being due to either shrinkage or gas. In practice, however, it is frequently difficult to tell the difference between porosity due to shrinkage and that due to gas from observing die castings. Accurate identification enables die casters to take corrective action. To identify the porosity accurately and to take corrective action in the die-casting process, the quantitative estimation of the morphology of pores such as their shape or spatial distribution can be a source of useful information. In this study, two types of fractal analyses are proposed to characterize the porosity in terms of the shape of individual pores and the spatial distribution of multiple pores. It is shown that these are indicators of whether the predominant cause of the porosity is shrinkage or gas. These parameters are expected to indicate the action that should be taken to manufacture pore-free die castings. [doi:10.2320/matertrans.MRA2007314]