Metallurgical Aspects of Inclusion Assessment in Al–6%Si Casting Alloy Using the LiMCA Technique

Abstract

In the production of high-quality aluminum castings, melt cleanliness is important in regard to the performance and quality of the cast part and is determined, among other factors, by the inclusions present in the molten metal. Besides causing problems in process and quality control, other harmful consequences include reduced mechanical properties, poor machinability and increased porosity. Thus, control of melt cleanliness requires monitoring and minimizing the presence of impurities and inclusions. The liquid metal cleanliness analyzer (LiMCA) technique was used in the present study to investigate its capability for measuring inclusions such as Al2O3, Al4C3, MgO, CaO, TiB2 and TiAl3 typically found in aluminum alloys, where these inclusions were added to Al–6%Si alloy melts using powder, master alloy, pure metal and metal matrix composite sources. Melts containing the different inclusion types were prepared, and the melt cleanliness was quantified using the LiMCA technique. Samplings for microstructural examination were also taken simultaneously. Evidence of the agglomeration of a vast amount of TiB2 inclusions as captured by the LiMCA probe tube shows that LiMCA is the only technique that is able to capture such agglomerates in-line, without any problem, as other techniques such as the PoDFA and Prefil cannot measure such TiB2 agglomerates without their filter systems getting clogged and interrupting the measurements. This is a significant finding and demonstrates a very important aspect of the LiMCA technique, particularly in view of the fact that Al–Ti–B master alloys are regularly employed for grain refining aluminum casting alloys.