The high-temperature oxidation behaviour of three hot-work tool steels, Dievar, H11 and W600, was investigated by simultaneous thermal analysis (STA). Since the steels studied are usually used in the ...heat-treated condition, the high-temperature oxidation was studied in two conditions, the soft-annealed condition and the hardened and tempered condition. Simultaneous thermal analysis was used to study the effects of temperature, chemical composition and thermal condition of the steels on the high-temperature oxidation kinetics. The samples were oxidised for 100 h in air atmosphere in the STA instrument. The temperature range studied was between 400 and 700 °C. The equations describing the high-temperature oxidation kinetics were derived from the STA results. The kinetics can be described by three mathematical functions, namely exponential, parabolic and cubic. However, which function best describes the kinetics depends on the oxidation temperature, chemical composition and thermal state of the steel. Hardened and tempered samples have been shown to oxidise less, resulting in a slower oxidation rate. In addition, steels containing chromium (H11 and Dievar) generally oxidise less than a steel without chromium (W600).
The present study comprises an investigation involving thermodynamic analysis, microstructural characterisation, and a comparative examination of the solidification sequence in two different ...aluminium alloys: EN AW 6026 and EN AW 1370. These alloys were modified through the addition of pure indium and a master alloy consisting of indium and bismuth. The aim of this experiment was to evaluate the potential suitability of indium, either alone or in combination with bismuth, as a substitute for toxic lead in free-machining aluminium alloys. Thermodynamic analysis was carried out using Thermo-Calc TCAL-6 software, supplemented by differential scanning calorimetry (DSC) experiments. The microstructure of these modified alloys was characterised using SEM–EDS analysis. The results provide valuable insights into the formation of different phases and eutectics within the alloys studied. The results represent an important contribution to the development of innovative, lead-free aluminium alloys suitable for machining processes, especially for use in automatic CNC cutting machines. One of the most important findings of this research is the promising suitability of indium as a viable alternative to lead. This potential stems from indium’s ability to avoid interactions with other alloying elements and its tendency to solidify as homogeneously distributed particles with a low melting point. In contrast, the addition of bismuth does not improve the machinability of magnesium-containing aluminium alloys. This is primarily due to their interaction, which leads to the formation of the Mg3Bi2 phase, which solidifies as a eutectic with a high melting point. Consequently, the presence of bismuth appears to have a detrimental effect on the machining properties of the alloy when magnesium is present in the composition.
In this research enthalpy balance analysis of the EN AW 5182 aluminium alloys during entire process path of sheet production was made, whereas samples after every step of sheet production process ...path were obtained. Using Thermo-Calc computer program thermodynamic simulation of equilibrium and nonequilibrium solidification was made. Differential scanning calorimetry was made on every sample, whereas the melting characteristic temperatures and the melting enthalpies from the results were obtained. Optical microscopy and scanning electron microscope with energy-dispersive X-ray spectroscopy were used to analyse microstructure and microstructural components. It was found that each step of the process, involving different processing temperatures and deformation, has a significant effect on the reaction/melting enthalpy and cannot be uniquely described. Homogenization reduces and intermediate annealing of the hardened sheet increases the melting enthalpy. Hot rolling has a significant effect on the melting enthalpy, while cold rolling has only a minor effect.
The aluminium alloy AA 6086 attains the highest room temperature strength among Al-Mg-Si alloys. This work studies the effect of Sc and Y on the formation of dispersoids in this alloy, especially L1
...-type ones, which can increase its high-temperature strength. A comprehensive investigation was carried out using light microscopy (LM), scanning (SEM), and transmission (TEM) electron microscopy, energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), differential scanning calorimetry (DSC), and dilatometry to obtain the information regarding the mechanisms and kinetics of dispersoid formation, particularly during isothermal treatments. Sc and Y caused the formation of L1
dispersoids during heating to homogenization temperature and homogenization of the alloys, and during isothermal heat treatments of the as-cast alloys (T5 temper). The highest hardness of Sc and (Sc + Y) modified alloys was attained by heat-treating alloys in the as-cast state in the temperature range between 350 °C and 450 °C (via T5 temper).
Abstract Aluminium alloys are popular in modern applications due to their lightweight, high strength and ductility. Alloys in the 8xxx series have similar properties to those in the 1xxx series, but ...are stronger, are more malleable and have higher stiffness. The addition of rare earths (RE) can refine the as-cast microstructure and, as a result, can increase the corrosion resistance and mechanical properties of aluminium alloys at room and high temperatures. The effects of rare earth (Ce and/or La) additions to Al-1.4Fe alloys were investigated. Thermal analysis of the solidification behaviour of the reference alloy showed the occurrence of three reactions corresponding to the formation of α-Al, eutectic (α-Al + Al x Fe y ) and Fe intermetallics, respectively. The results showed similar reactions for the Ce- and/or La-modified alloy, but at slightly different temperatures, indicating a change in the forming phases due to the addition of Ce and/or La. In all cases, the microstructures were typically hypoeutectic, consisting of the primary α-Al and the eutectic (α-Al + Al x Fe y ). The effect of grain refinement of the primary α-Al grains of the as-cast alloy was observed by the addition of RE, while La showed the strongest effect. The effect of the RE additions showed no obvious differences in the morphology of the eutectic Al x Fe y , although they were present in these phases. When Ce and/or La were added, (α-Al + Al 11 Ce 3 ) and/or (α-Al + Al 11 La 3 ) eutectics were formed, while Fe was not detected in these eutectics.
Abstract The high-strength aluminium alloys of the 7xxx series, which belong to the Al–Zn–Mg–Cu system, are known for their exceptional properties and are often used for applications where strength, ...fatigue resistance, stress corrosion resistance and wear resistance are required. The alloy EN AW-7175 requires an understanding of the precipitation process during solidification and cooling, where different phases are formed depending on the Zn/Mg ratio and cooling rate. Microstructural defects in the as-cast state affect the mechanical properties, prompting the investigation of La additions to refine the microstructure and improve the mechanical properties. In this study, the influence of La additions on the solidification and microstructure of the alloy EN AW-7175 in the as-cast state is investigated. Thermodynamic calculations, DSC and SEM analyses were performed. Samples with La additions (0.05–0.17 mass%) were compared with a reference sample (0 mass% La). La additives have only a minimal effect on the liquidus temperature and show minor differences in the solidus temperature in equilibrium calculations. The solidification interval decreases slightly compared to the reference sample, which is consistent with the Scheil simulations. The DSC results show reduced liquidus and solidus temperatures, while the solidification interval remains largely unchanged by the addition of La. The addition of La alongside Al 13 Fe 4 , Mg 2 Si and the eutectic α(Al) + σMg(Zn, Cu, Al) 2 leads to the formation of two new La-based phases: Al 20 Cr 2 La and LaSi 2 . Al 20 Cr 2 La modifies the Al 45 Cr 7 phase and solidifies first, while LaSi 2 modifies Mg 2 Si. As the La content increases, the Mg 2 Si content decreases until it completely disappears at a La content of more than 0.1 mass%. On the contrary, according to the literature, the grain size increases somewhat with a higher La content.
During the die-casting process as well as the hot forming process, the tool is subjected to complex thermal, mechanical, and chemical stresses that can cause various types of damage to different ...parts of the tool. This study was carried out to determine the resistance of various tool steels, i.e., UTOPMO1, HTCS-130, and W600, in molten Al99.7 aluminum alloy at a temperature of 700 °C. The formation kinetics of the interaction layer between the molten aluminum and tool steels was studied using differential scanning calorimetry. Light and field-emission scanning electron microscopy were used to analyze the thickness and nature of the interaction layers, while thermodynamic calculations using the Thermo-Calc software were used to explain the results. The stability of the HTCS-130 and W600 tool steels is better than the stability of the UTOPMO1 tool steel in the molten Al99.7 aluminum. Two interaction layers were formed, which in all cases indicate an intermetallic Al
Fe
layer near the aluminum alloy and an intermetallic Al
Fe
layer near the tool steels, containing small round carbides. It was confirmed that Ni reduces the activity of aluminum in the ferrite matrix and causes a reduction in the thickness of the intermetallic layer.
Within the scope of this research the transformation of the Al6Fe metastable phase was analyzed via Differential Scanning Calorimetry (DSC), optical and Scanning Electron Microscopy (SEM) and X-ray ...Diffraction (XRD). A binary Al-Fe1.1 low-impurity alloy was produced with refined raw materials in a controlled environment. With a cooling rate of 35 K/s, solidification of the Al6Fe metastable phase was achieved. The samples were homogenized at 600 °C for 2–24 h. Results of a qualitative analysis of metallographic samples show that the transformation began on grain boundaries, forming an Fe-phase free region, but after 2 h began to take place within the eutectic region. The transformation is mostly complete after 12 h, but after 24 h of homogenization it is fully complete as all samples, except the 24 h homogenized one, contain both the metastable Al6Fe and the stable Al13Fe4 phase.
High pressure die casting is one of the leading casting processes in the modern industry. In the case of high pressure die casting, the melt is in contact with the tool, whereas the chemical ...interaction between the tool, made of hot-work tool steel and the melt occur. In addition, mechanical and heat wear of the tools also occur. For high productivity high resistance to these factors is required. The interaction between molten aluminium alloys Al99.9, Al99.7 and AlSi12 and hot-work tool steel UTOPMO1 was investigated at various experimental temperatures, i.e. 670 °C and 700 °C, whereas the differential scanning calorimetry was used. Optical and scanning electron microscopy were used in order to analyse interaction layer. The result of the interaction is the growth of a reaction layer, which is formed from intermetallic phases from Al–Fe or Al–Fe–Si systems. Reaction layer varies regarding the aluminium alloy and the temperature, to which it is exposed, whereas it is composed of three or four different layers. The thickness of the interaction layer depends only from the temperature, but the number of different layers in the interaction layer depends from the type of the aluminium alloy.
Lab-scale investigations on the processing of small powder volumes are of special importance for applications in additive manufacturing (AM) techniques. Due to the technological importance of ...high-silicon electrical steel, and the increasing need for optimal near-net-shape AM processing, the aim of this study was to investigate the thermal behavior of a high-alloy Fe-Si powder for AM. An Fe-6.5wt%Si spherical powder was characterized using chemical, metallographic, and thermal analyses. Before thermal processing, the surface oxidation of the as-received powder particles was observed by metallography and confirmed by microanalysis (FE-SEM/EDS). The melting, as well as the solidification behavior of the powder, was evaluated using differential scanning calorimetry (DSC). Due to the remelting of the powder, a significant loss of silicon occurred. The morphology and microstructure analyses of the solidified Fe-6.5wt%Si revealed the formation of needle-shaped eutectics in a ferrite matrix. The presence of a high-temperature phase of silica was confirmed by the Scheil-Gulliver solidification model for the ternary model Fe-6.5wt%Si-1.0wt%O alloy. In contrast, for the binary model Fe-6.5wt%Si alloy, thermodynamic calculations predict the solidification exclusively with the precipitation of b.c.c. ferrite. The presence of high-temperature eutectics of silica in the microstructure is a significant weakness for the efficiency of the magnetization processes of soft magnetic materials from the Fe-Si alloy system.
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