The Quantitative Discrimination between Shrinkage and Gas Microporosity in Cast Aluminum Alloys Using Spatial Data Analysis

Microporosity in cast aluminum alloys may originate from hydrogen gas evolution, microshrinkage, or a combination of both. A spatial analysis method for the quantitative discrimination between shrinkage and gas porosity is presented and explained. It is shown that shrinkage pores can be selected and analyzed separately from gas pores by nearest-neighbor analysis. The principles of spatial statistics are discussed, and the types of spatial point patterns, complete spatial randomness, and nearest-neighbor cluster analysis are reviewed with respect to microporosity analysis. The pore distribution of a cast Al–7% Si (A356) foundry alloy is used as an example.