G. Piwowarski

Determining Temperature Dependencies of Sand Mould Thermal Properties

The presented work is aimed at determining thermal diffusivity, thermal conductivity and heat capacity coefficients of silica quartz bentonite foundry sand. The values of the above thermo-physical properties were determined for temperature range of about 30 - 450 °C using the Casting measuring method [1-. The results obtained during the examinations presented in the paper can be useful when formulating boundary conditions in numerical models of heat and mass transfer in the system: casting mould ambient. The Casting method allows preserving real conditions during the experiment, i.e. contact of the mass with liquid metal and solidifying casting, and the obtained results are in a good agreement with the mean values available in literature. From the obtained results it follows that examinations should be also focused on thermo-physical properties vs. mass density dependency.

The efficiency analysis of grain refinement in high-zinc aluminium alloys with Ti-containing master alloy

ABSTRACT The paper concerns double high-zinc aluminium alloys inoculated with master alloys containing titan and comprises research on the influence of inoculation on grain refinement. Most aluminium alloys before being cast have relatively low strength properties and therefore a series of treatments are applied in order to improve these properties. One of the treatments is the grain fragmentation process, called grain refinement treatment that allows to improve material properties of alloy, improve the feeding properties during the casting solidification, as well as to obtain more robust machinability of casting. Al alloy with 20wt% Zn (AlZn20) was tested, inoculated with the addition of traditional master alloy AlTi3C0.15 before casting to the sand mould. The results obtained during the studies show nucleating activity of the master alloy, proved by reduced overcooling and recalescence on cooling curves. Additionally, the role of titanium in this process is explained.

Property enhancement by grain refinement of zinc-aluminium foundry alloys

Development of cast alloys with good mechanical properties and involving less energy consumption during their melting is one of the key demands of todays industry. Zinc foundry alloys of high and medium Al content, i.e. Zn-(15-30) wt.% Al and Zn-(8-12) wt.% Al, can satisfy these requirements. The present paper summarizes the work [1-9] on improving properties of sand-cast ZnAl10 (Zn-10 wt.% Al) and ZnAl25 (Zn-25 wt. % Al) alloys by melt inoculation. Special attention was devoted to improving ductility, whilst preserving high damping properties at the same time. The composition and structural modification of medium- and high-aluminium zinc alloys influence their strength, tribological properties and structural stability. In a series of studies, Zn - (10-12) wt. % Al and Zn - (25-26) wt.% Al - (1-2.5) wt.% Cu alloys have been doped with different levels of added Ti. The melted alloys were inoculated with ZnTi-based refiners and it was observed that the dendritic structure is significantly finer already after addition of 50 - 100 ppm Ti to the melted alloys. The alloys structure and mechanical properties have been studied using: SEM (scanning electron microscopy), LM (light microscopy), dilatometry, pin-on-disc wear, and tensile strength measurements. Grain refinement leads to significant improvement of ductility in the binary high-aluminium Zn-(25-27) Al alloys while in the medium-aluminium alloys the effect is rather weak. In the ternary alloys Zn-26Al-Cu, replacing a part of Cu with Ti allows dimensional changes to be reduced while preserving good tribological properties. Furthermore, the high initial damping properties were nearly entirely preserved after inoculation. The results obtained allow us to characterize grain refinement of the examined high-aluminium zinc alloys as a promising process leading to the improvement of their properties. At the same time, using low melting ZnTi-based master alloys makes it possible to avoid the excessive melt overheating needed for TiCAl or TiBAl refiners and reduces the possibility of gas pick-up and material loss.