Austrian Foundry Research Institute

Sand cores and moulds form the inner and outer structures of casting parts with tolerances of up to a few tenths of a millimetre. These must fulfil two complementary characteristics. During casting, they must withstand the high thermal and mechanical loads and subsequently disintegrate without leaving any residue. The production of these mostly organically bonded cores and moulds is done with conventional manufacturing processes, such as core shooting, or what is becoming increasingly more important for foundries, using 3D printing. In order to better understand this complex disintegration behaviour of these different core types and thus minimise the enormous energy input for their removal, a suitable simulation model based on discrete element methods (DEM) is considered as a tool to describe and further analyse the prevailing complex interactions in more detail. This contribution discusses the characterisation of furan resin bonded sand cores/parts, presenting various test apparatuses designed for this purpose, and outlines the foundational setup and definition of bonded-particle models (BPM) to be used as breakable structures in respective DEM simulations.

Al-7Si-0.3Mg based alloys have been widely used. Nevertheless, at least three issues during melt treatment (grain refinement of Al grains, modification of eutectic Si and refinement of eutectic grain size) need to be further explored. In this contribution, we focus on these three melt treatments. For grain refinement of Al grains, the stochiometric Al-2.2Ti-1B grain refiner rod together with 0.12 wt. % Ta was used. For modification of eutectic Si, Eu up to 500 ppm was used. The best modification can be obtained with 200 ppm Eu. By further increasing Eu up to 500 ppm, modification level becomes worse due to the formation of Al2Si2Eu. For the refinement of eutectic grain size, a combined addition of Eu (up to 500 ppm) and P (up to 40 ppm) was used. With increasing P concentration, the modification of eutectic Si became worse. The size of eutectic Si increases, the shape factor of eutectic Si decreases. When the P concentration is higher, more Eu is needed for a well-modified eutectic Si. This investigation provides a novel concept for melt treatment of Al-Si-Mg based alloys.

Entrained droplet technique and DSC analyses were employed to investigate the influence of trace elements of Sr, Eu and P on the heterogeneous nucleation of entrained eutectic Si in high purity melt spun Al-5wt.% Si alloys. Sr and Eu addition was found to exert negative effects on the nucleation process, while an increased undercooling was observed. This can be attributed to the formation of phosphide compounds having a lower free energy and hence may preferentially form compared to AlP. Only a trace P addition was found to have a profound effect on the nucleation process. The nucleation kinetics is discussed on the basis of the classical nucleation theory and the free growth model, respectively. The estimated AlP patch size was found to be sufficient for the free growth of Si to occur within the droplets, which strongly indicates that the nucleation of Si on an AlP patch or AlP particle is a limiting step for free growth. The maximum nucleation site density within one droplet is directly related to the size distribution of AlP particles or AlP patches for Si nucleation, but is independent of the cooling rates. Although the nucleation conditions were optimized in entrained droplet experiments, the observed mechanisms are also valid at moderate cooling conditions, such as in shape casting.

Ultrasonic processing is known to be an efficient means of aluminium melt degassing and structure modification with additional benefits of being economical and environment friendly. The present paper reports on the kinetics of ultrasonic degassing and regassing of foundry aluminium alloys and on pilot scale degassing trials. Efficiency of ultrasonic degassing is compared with conventional Ar rotary degassing. Direct measurements of hydrogen concentration in the melt by Foseco Alspek-H probe are used along with reduced pressure test. The effects of ultrasonic processing on porosity are studied using three-dimensional X-ray tomography.