Papers by Author: Zoltán Gácsi

Abstract: In the general practice of ED-XRF measurements, the values of elemental concentrations are derived from complicated calculation methods. Hereby a simple mathematical formula is suggested, which provides an easy way to prepare standard samples. On the other hand, the simulation of spectral lines may also be a helpful tool for the calibration process. In this study, measured and simulated data were used for the quantitative analysis of ternary Au-Ag-Cu alloys. To determine the calibration points, the peak intensity ratio method was applied and the calibration curves were fitted. This work presents the results of a twofold investigation aimed at: a) finding a suitable computational tool to optimise the parameters of the underlying equations and b) testing the reliability of the simulated data to determine the concentrations of multi-element standard samples. Based on comparisons of calculated concentrations it can be stated that a simple calculation method with simulated data provides an easy tool to define calibration standards. It is also demonstrated that the parameters of the linear plots can be optimised to yield improved results.

Abstract: In this study the effects of small amounts of nickel addition (0-2000 ppm) on the microstructure, on Cu6Sn5 intermetallic compound formation and the mechanical properties of a Sn-0.5Cu lead-free solder were investigated. It is known that even ppm level additions of Ni have significant effects on the microstructure of Sn-Cu solder alloys. Ni suppresses the growth of β-Sn dendrites in favour of eutectic formation. As the nickel content increases, the microstructure undergoes a morphology evolution from hypoeutectic through fully eutectic to hypereutectic. Furthermore, the presence of Ni in the Cu6Sn5 intermetallic compound phase stabilises its high-temperature allotrope η-Cu6Sn5.

Abstract: Industry should gradually replace the tin-lead solder alloys used traditionally in the soft soldering technology by lead-free soldering alloys, which raises a lot of new technological and scientific problems to be solved. The introduction and application of lead-free alloys caused a number of soldering defects not observed earlier; mechanisms of their formation are still unclear. One of such defects is whisker formation, another one is intensified formation of intermetallic phases. The appearance of undesired intermetallic phases in the soldering material spoils its mechanical properties; therefore it is particularly important that these phases do not form in electronic components. Besides, the formation of intermetallic compounds may occur in the soldering bath, thus making the soldering process difficult or even impossible.Tin-copper-nickel and tin-silver-copper alloys are suitable for the replacement of tin-lead alloys. The components of these alloys were studied. After metallographic examination of the specimens the occurrence of intermetallic phases was determined by the XRD method. The identification of intermetallic phases was carried out by using literature data and phase diagrams.

Abstract: Whiskers formed on the lead-free tin surfaces pose a serious risk to small electronic devices causing a short circuit and leading to the component/device failure. The present research was focused on the investigation of tin whisker formation on a motor control unit sockets made of tin coated copper, applying to the specimen mechanical load alone or together with heat treatment/electric current. Scanning Electron Microscopic (SEM) imaging was applied in order to study the microstructure of tin whiskers obtained, their length and number at the boundary of each imprint. If the mechanical stress increases from 1000 to 5000 MPa, the average number of whiskers and possible formation spots also increase from 570 to 1300. The length of whiskers varied from 3 μm after 0.5 h to 5.5 μm after 3 hours of exposition. It has been found that heat treatment at 150°C for 1 hour significantly reduces the number of whiskers (on average 6 times as few) formed. Therefore, the threat of failure of the electronic equipment is reduced.

Abstract: Al/SiC composites are used especially in automotive and aerospace industry due to the numerous advantageous mechanical properties. These end-products can be produced by casting or powder metallurgical techniques. High strength with high toughness can be reached only by perfect interfacial bonds between the matrix and reinforcing phase. To improve the interfacial bond, one of the methods is the surface coating of the SiC particles. But the metal layer of the reinforcing phase reacts with the matrix due to the high sintering temperature and long sintering time. In our research work the formation of Al-Ni intermetallic phase was investigated by Scanning electron microscopy (SEM) and X-ray diffraction measurements (XRD).

Abstract: Automotive castings have to meet more and more versatile requirements these days. One of the most important requirements towards suppliers and foundries is producing parts of better quality, higher performance but at the same time of less weight. In order to couple this small weight with high performance and excellent quality these products should meet very strict mechanical standards of automotive parts. There is a constant need for production engineering developments ranging from purity degree - that is producing molten metal with high cleanness - to grain refinement and alloy improving including heat treatment technologies.

Abstract: One of the methods of melt-treatment of Al-Si alloys is the modification that plays a very significant role in the development of (mechanical) properties of finished product. There are a lot of well-known processes for the investigation of effectiveness of modification but an objective, exact result cannot be obtained in each case by using these methods. The method suitable for the classifi-cation of modification worked out by us was developed by integrating two methods namely the comparison by means of etalon-images and the integration of measurement of morphological pa-rameters. This method is relatively simple, does not demand lots of measurements and gives reliable results.

Abstract: The A356 alloy, which consists of 100-200 ppm modifier, namely strontium was examined. The samples were solidified unidirectionally, and each sample had a pair which was solidified in a rotating magnetic field. The microstructure of the samples: morphology and the fraction of eutectic silicon was studied. The morphology of eutectic Si was very different in the samples - the samples solidified at different movement velocities – so it was necessary to determine the quantity of strontium. Magnetic stirring changes both the strontium content and the extent of modification. This paper describes the investigation methods and the effects of strontium modification.

Abstract: The purpose of this study is to find a relationship between the parameters describing the microstructural homogeneity of SiC particle reinforced Al metal matrix composites. The Al-SiC powder mixtures having different particle size combinations were hot-pressed after careful mixing. The optical microscope images of the microstructures were processed by using an image analyzing program; the binary morphology was chosen for characterizing the SiC particle distribution.

Abstract: Color etching is a widely used technique for visualizing different phases in metallic materials. Its advantage to the traditional etching techniques is that it gives additional information within one phase, namely, the color shade of a given phase can change in a certain range. This paper demonstrates that, due to the physics of the color etching, the shade of a phase also depends on the crystallographic orientation of the investigated grain. As a test material, spheroidal graphite cast iron was used, and individual grain orientation was identified by automated electron back scattering diffraction (EBSD). Results showed that there is a strong correlation between grain orientation and the shades obtained by color etching.