Metallographic Investigation and Solidification-Structure Modelling of Al Micro Castings

J-F. Charmeux, R. Minev, S. Dimov, E. Minev
Manufacturing Engineering Center, Cardiff University, Cardiff, CF24 3AA, UK

Abstract

Producing micro-castings trough vacuum investment casting is known to be associated with high cooling rates due to small scale of the castings. High cooling rates together with alloy composition might be the main factors affecting the final metallographic structure of castings’ alloys during the solidification process. When using Al-Si-Mg casting alloys, the size of the dendritic structure can be used for a non-destructive test to assess the mechanical properties and overall quality of the castings. Also the ability of the alloys to be structured by different mechanical and energy assisted processes is highly dependant on their metallographic structure. This paper investigates the structural changes occurring when shifting from conventional size castings to micro-castings. An empirical model describing the degree of dendrite cell refinement as a function of micro-castings aspect ratio is proposed. Additionally, the paper reports the changes in porosity and Si particles morphology observed on micro-castings produced with different flask temperatures. MHV measurements were also performed for different aspect ratio of the cast micro-features.