Advanced Materials Research Vol. 1128

Abstract: In the paper are presented the techniques for obtaining metallic foams based on copper. The permeability of them is described. The metal foams in this case are made from a mixture of copper and NaCl in well-established proportions (20%, 30% and 40% Cu), pressed (the mixture) in mould and sintered at temperatures of 780°C and 830°C. Proper knowledge’s of the permeability (K) are important and should be defined properly [1]. The present study was carried out to have an understanding the influence of different permeability values for different NaCl concentrations in the foams. The necessary equipment was adapted for this purpose. The permeability values obtained for this reason was correlated with the pore size and number of pores per square centimeter. With the increasing of pore diameters and copper proportion the increasing of permeability of metallic foams was also measured.

Abstract: Solidification simulation software was developed, for parts having rotational symmetry cast of eutectic alloys or pure metals. The software uses a finite differences mathematical model described in cylindrical coordinates. Unlike software in Cartesian coordinates, it allows the solidification simulation for three dimensional parts with rotational symmetry using 2D simulation. As result the effective simulation time is much smaller (tens or even hundreds of times) in comparison with simulation in Cartesian coordinates. Cylindrical coordinates have the advantage of allowing a precise reproduction of the round contour parts. The paper presents the experimental verification of the results provided by the software. Experimental verification is performed by thermal analysis. A cylindrical sample with a diameter D = 60 mm and length L = 150mm was cast. The part was cast in Al-Si eutectic alloy (ATSi12). The temperature variation inside casting was recorded in three points: in the center, at the distance 1/2R and on the part surface. The experimental results were compared with those determined by computer solidification simulation. The values for liquid alloy initial temperature and for landing eutectic temperature used in simulation were chose accordingly to those experimentally determined for each point separately. The temperature variation curves during casting cooling and solidification obtained by simulation are close to those experimentally determined. The curves approaching in the first part (cooling in liquid state and solidification) can be appreciated as very good. Small differences appear in the final of the curves in the cooling area after the complete solidification of the alloy in that point. The experiment revealed that the tested software provide accurate data on castings solidification (solidification time and temperature distribution). As result, the software developed by the authors from Transilvania University, can be used with enough accuracy for fundamental and applied researches related to castings solidification.

Abstract: The structure and properties of grey cast iron castings are considerably influenced by the cooling rate during solidification. In order to obtain grey cast iron parts with a hard superficial layer (wear resistant), external metallic coolers are placed on those surfaces during casting. This is the case of cam pushers, camshafts, driving shafts, metalworking rolls, etc. Cast iron coolers or steel coolers are mostly used in practice. The cooling rate during solidification is influenced by the thermo-physical characteristics of the coolers. This paper presents the results obtained by simulation and experimental research on coolers material influence on the structure and hardness of the surface layer of a pearlitic cast iron sample. It was studied the solidification of samples with dimensions 20 x 20 x 60 mm, cast of pearlitic cast iron in six variants: without a cooler and in the presence of some metallic coolers of different thermo-physical characteristics (iron, steel, copper, titanium and aluminum coated with a thin layer of steel). It was studied the influence of cooler material on structure of the superficial layer, on thickness of the hardened layer, on superficial hardness, on the temperature field and cooling rates. Conclusions are drawn regarding these influences and the possibility of using external coolers in industrial practice.

Abstract: The main purpose of this study is to determine by experimental research the influence both of pouring temperature and cup samples size and their filling level on the cooling curves parameters at cast iron solidification. For the experiment it follows to determine the less sensitive parameters to pouring conditions both for reduced and normal cup samples. By using two cups with different cooling modulus it was established some correlation between some variable factors such as cooling modulus, sample filling level and casting temperature and the cooling curves parameters. The experimental results released a higher sensitivity of reduced size cup (lower cooling modulus) on pouring conditions (pouring temperature and mould cup filling level).

Abstract: Thermal analysis is worldwide used in foundry for control of structure and properties of cast irons. In this paper is presented the experimental study realized to control the inoculation effect by thermal analysis method of inoculated grey cast irons. For this purpose was conducted an in ladle inoculation process with 0.5wt. % inoculant from LaCaAlFeSi and BaCaAlFeSi alloy systems. The main goals of this experimental research work are: to determine the particular characteristics of the registered cooling curves, to notice the solidification parameters that present sensibility as against inoculant addition in treated cast iron and eventually to improve thermal analysis technique of cast irons.

Abstract: Heat treatable aluminum alloys and other alloys with similar properties are the most widely used light alloys in aeronautical construction [1-3]. These alloys have (i) high resistance to crack initiation and propagation, (ii) resistance to developing a strong lift force of the wings, (iii) high temperature, (iv)creep and fatigue vibration resistance. These age hardening Al alloys, are designed to take the mechanical stresses of the aircraft during flight. To achieve and continually improve these characteristics are necessary studies and researches on optimizing the manufacturing technological process of these types of Al alloys. This paper presents theoretical and experimental development of aluminum prealloys and high purity 2xxx Al alloys series elaboration for the aviation industry. We aimed to obtain higher energy efficiency, a better protection against gases, development of melt refining decontamination during casting. We are taking into account that the AlCu3.3Mg1.5Mn alloy has in chemical composition besides the alloying elements also a limited percentage of impurities (eg. 0.15% Si and 0.20% Fe), impurities difficult to remove from molten aluminum. In these conditions, the manufacturing processing requires some precautions such as: cleaning melting furnace and the correct choice of materials composing the charge in order to prevent contamination of the bath. The casted and homogenized Al alloys were analyzed in terms of composition and microstructure.

Abstract: Tungsten carbide is the choice of predilection for producing parts requiring good wear resistance. In this context it is produced in large quantities by the carburization of tungsten trioxide under a stream of hydrogen at elevated temperature followed by grinding to achieve the required fineness. This work aims to study the conditions in which tungsten carbide can be produced by mechanical alloying method. Using this method would facilitate obtaining carbide through a simple and easy to use technology without prohibitive costs, directly by an end user. For this purpose the thermodynamic study is conducted to establish the conditions under which the carburizing reaction can take place. The condition for the reaction to occur spontaneously is reaching a temperature of 621°C. Carrying out this reaction in a system without external energy input seems impossible. Mechanical alloying experiments were carried out in a Fritch Pulverisette 7 premium line planetary mill, equipped with two bowls of 80ml capacity lined with sintered tungsten carbide. Each bowl contained 200 g of tungsten carbide balls with dimensions of 10 mm and 12 mm. The balls/load ratio was 10:1. Grinding was performed in steps of 3 hours, with breaks for sampling, with rotation speeds of 600 and 800 rpm. Tests conducted showed complete conversion of raw materials into tungsten carbide after different durations of time.

Abstract: Metallic mould properties are influenced by the technological process used on casting. The mechanical properties of aluminium castings can be affected by dissolved gases, heterogeneous impurities or shrinkage remaining in casting after solidification. Dissolved gases and oxide inclusions in aluminium all have a deleterious effect on casting quality. The treatment of molten aluminium using vibrations and salts was found to be highly efficient in refining the microstructure of the alloy. The main objective of the paper is to understand the effects of vibrations and salts treatment on the final microstructure and changes that take place and influences aluminium alloy properties used in mould manufacture. The microstructural changes have a great significance in improving the properties of aluminium alloy castings. Understanding this effects and the modification mechanism can undoubtedly be of great significance for improving casting quality. Fluxes based on a KCl-NaCl mixture may be used to cover and protect the metal from oxidation. Most fluxes are based on a mixture of KCl and NaCl, which forms at low-temperature (665 °C) eutectic.

Abstract: This paper presents the experimental results of the effects of the pressing speed on the press ability of the cementite powders alloyed with iron powders, in order to obtain sintered steels. Cementite or iron carbide is a chemical compound with Fe₃C formula having orthorhombic crystal structure. Regarding mechanical properties, cementite is hard and brittle being important in the metallurgical processes. For the research process was used a mixture consists by cementite and iron powders (6,75%Fe₃C+93.25%Fe) which was obtained by mechanical alloying technique for 30 hours. The cementite powders were produced by direct carburizing of Fe powders. The mixture was unilateral die pressing at three pressures 200, 400 and 600 MPa respectively 5 pressing speeds 10 up to 50 mm/min. The green billets were sintered in argon atmosphere and were studied by microstructural point of view. The evolution of microhardness function the pressing parameters was studied too.