Effect of Chill Parameters on the Residual Strain in Cast 319 Aluminum Alloy: A Neutron Diffraction Study

摘要

The demand for light weight vehicles continues to stimulate extensive research into the development of light weight casting alloys and optimization of their manufacturing processes. Of primary relevance are Aluminum (Al) and Magnesium (Mg) based alloys, which have successfully replaced selected iron based castings in automobiles. However, optimization of as-cast microstructure, processing and performance remains a challenge for some Al-based alloys. In this context, placement of chills in castings has been frequently used to locally manipulate the solidification conditions and microstructure of a casting. In this work, the effect of using an active copper chill on the residual strain profile of a sand-cast B319 aluminum alloy was investigated. Wedge-shaped castings were produced with three different cooling conditions: copper plate chill, copper pipe with cooling water and no chill (baseline). The effect of chill condition on the variation of residual strain in the casting was investigated using neutron diffraction approach. Diffraction from (111) and (311) reflections was studied and revealed that the (311) reflection did not exhibit appreciable strain variation at different chill conditions. In contrast, the (111) reflection exhibited a mix of tensile and compressive strains which varied with a distance from the copper chill. A copper plate chill introduced a fluctuating pattern of strain profile with tensile and compressive strain peaks, while faster cooling (copper pipe with water flow) had attenuated the residual strain profile, suggesting the need to control the chilling condition in order to achieve optimal casting performance.