The External and Internal Shrinkages in Aluminum Gravity Castings

Abstract

In aluminum gravity castings, the external and internal shrinkages (micro-porosity) are more prominent than those in ferrous castings. In order to understand the relationship between these two shrinkages during solidification, three castings with various tilting angles (i.e., 0°, 45° and 90° designated as H- T-, and S- castings respectively) were designed.

Two pouring temperatures (700 and 760°C) were conducted in the real aluminum casting experiments. The volume change of external surface sinks was quantified by the reverse engineering scanning method, while that of internal porosities was measured by Archimedes method. Numerical models for simulating the shrinkages of aluminum alloy casting were suggested and validated by these experiments. The influence of tilting angle of castings was reported.

A linear function between maximum micro-porosity and pore formation pressure in the modeling result was proposed to predict the negative pressure within castings during solidification. Two feeding (liquid and mass feeding) mechanisms of the solidification in the real aluminum casting were clarified by the modeling results.