This paper presents a study of the effect of the modification and cooling rate on the grain count α(Al) in the Al-5Cu alloy. Research was
performed on castings with walls thickness between 3 mm and 25 mm. Cooling curves were recorded to determine the cooling rate and the
degree of undercooling at the beginning of solidification. It has been shown that cooling rate increases exponentially as the wall thickness
of casting decreases. Moreover it has been demonstrated that the cooling rate of castings changes within a wide range (21ºC/s - 1ºC/s)
when the wall thickness changes from 3 up to 25 mm. Metallographic examinations revealed primary grains (primary α(Al) grains). The
paper show that the relationship between the grain count and the degree of undercooling (for non-modified and modified alloys) can be
represented by the equation N = Nv = np·exp(-b/ΔTα), based on the Weibull's distribution of the size of nucleation sites.
The paper presents the results of tests on the spheroidising treatment of vanadium carbides VC done with magnesium master alloy and mischmetal. It has been proved that the introduction of magnesium master alloy to an Fe-C-V system of eutectic composition made 34% of carbides crystallise in the form of spheroids. Adding mischmetal to the base alloy melt caused 28% of the vanadium carbides crystallise as dendrites. In base alloy without the microstructure-modifying additives, vanadium carbides crystallised in the form of a branched fibrous eutectic skeleton. Testing of mechanical properties has proved that the spheroidising treatment of VC carbides in high-vanadium cast iron increases the tensile strength by about 60% and elongation 14 - 21 times, depending on the type of the spheroidising agent used. Tribological studies have shown that high-vanadium cast iron with eutectic, dendritic and spheroidal carbides has the abrasive wear resistance more than twice as high as the abrasion-resistant cast steel.
The paper discusses the reasons for the current trend of substituting ductile iron castings by aluminum alloys castings. However, it has been shown that ductile iron is superior to aluminum alloys in many applications. In particular it has been demonstrated that is possible to produce thin wall wheel rim made of ductile iron without the development of chills, cold laps or misruns. In addition it has been shown that thin wall wheel rim made of ductile iron can have the same weight, and better mechanical properties, than their substitutes made of aluminum alloys.
A eutectic reaction is a basic liquid-solid transformation, which can be used in the fabrication of high-strength in situ composites.
In this study an attempt was made to ensure directional solidification of Fe-C-V alloy with hypereutectic microstructure. In this alloy, the
crystallisation of regular fibrous eutectic and primary carbides with the shape of non-faceted dendrites takes place. According to the data
given in technical literature, this type of eutectic is suitable for the fabrication of in-situ composites, owing to the fact that a flat
solidification front is formed accompanied by the presence of two phases, where one of the phases can crystallise in the form of elongated
fibres.
In the present study an attempt was also made to produce directionally solidifying vanadium eutectic using an apparatus with a very high
temperature gradient amounting to 380 W/cm at a rate of 3 mm/h. Alloy microstructure was examined in both the initial state and after
directional solidification. It was demonstrated that the resulting microstructure is of a non-homogeneous character, and the process of
directional solidification leads to an oriented arrangement of both the eutectic fibres and primary carbides.
The excellent property combination of thin wall ductile iron castings (TWDI), including thin wall alloyed cast iron (e.g. austenitic TWDI) has opened new horizons for cast iron to replace steel castings and forgings in many engineering applications with considerable cost benefits. TWDI is considered as a potential material for the preparation of light castings with good mechanical and utility properties, the cost of which is relatively low. In this study, unalloyed and high Ni-alloyed (25% Ni) spheroidal graphite cast iron, with an austenitic metallic matrix were investigated. The research was conducted for thin-walled iron castings with 2, 3 and 5mm wall thickness, using different mould temperature (20°C, and 160°C) to achieve various cooling rates. The metallographic examinations i.e. characteristic of graphite nodules, metallic matrix, and primary grains of austenite dendrites (in high-nickel NTWDI) and mechanical properties were investigated. The study shows that homogeneity of the casting structure of thin-walled castings varies when changing the wall thickness and mould temperature. Finally, mechanical properties of thin-walled ductile iron castings with ferritic-pearlitic and austenitic metallic matrix have been shown.
The present research was conducted on thin-walled castings with 5 mm wall thicknesses. This study addresses the effect of the influence of
different master alloys, namely: (1) Al-5%Ti-1%B, (2) Al-5%Ti and (3) Al-3%B, respectively on the structure and the degree of
undercooling (ΔTα = Tα-Tmin, where Tα - the equilibrium solidification temperature, Tmin - the minimum temperature at the beginning of
α(Al) solidification) of an Al-Cu alloy. The process of fading has been investigated at different times spent on the refinement treatment ie.
from 3, 20, 45 and 90 minutes respectively, from the dissolution of master alloys. A thermal analysis was performed (using a type-S
thermocouple) to determine cooling curves. The degree of undercooling and recalescence were determined from cooling and solidification
curves, whereas macrostructure characteristics were conducted based on a metallographic examination. The fading effect of the refinement
of the primary structure is accompanied by a significant change in the number (dimension) of primary grains, which is strongly correlated
to solidification parameters, determined by thermal analysis. In addition to that, the analysis of grain refinement stability has been shown
with relation to different grain refinements and initial titanium concentration in Al-Cu base alloy. Finally, it has been shown that the
refinement process of the primary structure is unstable and requires strict metallurgical control.
The aim of this paper was to attain defect free, pure copper castings with the highest possible electrical conductivity. In this connection, the effect of magnesium additives on the structure, the degree of undercooling (ΔTα = Tα-Tmin, where Tα – the equilibrium solidification temperature, Tmin – the minimum temperature at the beginning of solidification), electrical conductivity, and the oxygen concentration of pure copper castings have been studied. The two magnesium doses have been investigated; namely 0.1 wt.% and 0.2 wt.%. A thermal analysis was performed (using a type-S thermocouple) to determine the cooling curves. The degree of undercooling and recalescence were determined from the cooling and solidification curves, whereas the macrostructure characteristics were conducted based on a metallographic examination. It has been shown that the reaction of Mg causes solidification to transform from exogenous to endogenous. Finally, the results of electrical conductivity have been shown as well as the oxygen concentration for the used Mg additives.
In this work, an assessment and comparison of the quality of selected bentonites and bentonite mixtures was made. The samples consisted of available foundry materials used for bonding green sands. Determining the homogeneity degree and specific surface area of the grains allowed us to compare the examined materials and determine their influence on other parameters. On the basis of a thermal analysis of the bentonites or bentonite mixtures, the changes occurring in the sample during its heating were determined. Determining the potential for ion exchange and montmorillonite content enabled us to assess the binding properties of the materials. The preparation of six green sands with different bentonites or bentonite mixtures gave us the opportunity to assess the changes in apparent density, permeability, compressive strength and friability as a function of humidity, and the impact of different materials on the mentioned parameters. Their charts were analyzed, and the molding sand with the addition of bentonite or a bentonite mixture was selected for which these parameters are favorable. On this basis, the best-presented binding material was assessed and selected.