Microstructural Fineness in Aluminum Castings

The role of Clemex software in this study

In order to measure secondary dendrite arms in aluminium alloy samples analyzed in this study, the participating research laboratories used Clemex image analysis software. Various types of microscopes, cameras and objectives were used in this study to determine the repeatability of the new Universal Mean Linear Dendrite Spacing formula across laboratories, operators and equipment. The Universal MLDS formula was applied to results from several samples exported from Clemex Vision software in a macro-based spreadsheet.

Authors: Devin R. Hess, Ph.D., Qigui Wang, Ph.D. GM Global Propulsion Systems, Pontiac, Michigan.

Abstract

In sand and permanent/semi-permanent mold casting processes, the hypoeutectic aluminum alloys of Al-Si-Mg and Al-Si-Cu-Mg solidify in a dendritic structure. It has generally been desired to have a fine dendritic structure for the best mechanical properties. The fineness of the dendritic structure is typically quantified by measuring the spacing between the secondary dendrite arms, referred to as the SDAS or DAS. While this is a widely accepted measurement technique no industry standard exists defining a consistent measurement process. This paper shows the variability identified between various laboratories and provides a method which significantly improves the repeatability in quantifying the fineness of the microstructure within these alloy systems and casting processes.

Keywords: aluminum, microstructure, secondary dendrite arm spacing, dendrite arm spacing, SDAS, DAS

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