Papers by Author: Andrzej Kiełbus

Abstract: Al-Si alloys are the most important group among aluminum casting alloys. They are widely used in automotive and aerospace industries. Chemical modification of the Al-Si alloys leads to formation of fine, fibrous Al-Si eutectic mixture ensuring high mechanical properties. The modification is however known to increase the alloy porosity, which may, in turn, result in decrease of its properties. The following paper presents results of the research on quantitative description of the Al-Si cast alloys porosity and influence of Na modification on the porosity of AlSi9Mg alloy. Porosity in the hypoeutectic Al-Si alloys occurs in four types: shrinkage cavities, shrinkage porosity, isolated gas pores and gas pores surrounded by shrinkage porosity. Na modification leads to increase of shrinkage pores volume fraction.

Abstract: The following paper presents results of the researches on the influence of Sr addition on microstructure and mechanical properties of EN AC-Al Si9Cu3(Fe) HPDC alloy. Two different elements were high pressure die cast for the research, one with Sr addition, second one without. Investigations involved light and scanning electron microscopy as well as hardness and tensile testing. EN AC-Al Si9Cu3(Fe) HPDC alloy microstructure is characterized by a fine dendrites of α-Al solid solution and AlSi binary eutectic mixture. What is more, many intermetallic phases are observed in the alloy. These are: α-Al₁₅(Fe,Mn,Cr)₃Si₂, β-A₅FeSi, A₂Cu, π-A₈Mg₃FeSi₆ and Q-A_l5Mg₈Cu₂Si₆. Sr modified alloy is characterized by a significant volume fraction of fine, fibrous AlSi-eutectic. The porosity in the modified alloy slightly decreased. Mechanical properties of the alloy increased after Sr modification.

Abstract: Following article summarizes results of the researches concerning influence of heating and cooling rate on the phase transformations temperatures in EV31A magnesium alloy. Particular attention has been paid to calibration aspects of the temperature measurement as well as cooling and heating rates in protective atmosphere. The researches were conducted on Multi HTC calorimeter, provided by Setaram company. The samples were heated up to liquidus temperature with controlled rates of: 2.5°C/min, 5°C/min, 10°C/min, 15°C/min and 20°C/min. Just after melting, the specimens were cooled with the same rates. Equilibrium temperatures of phase transformations were calculated by extrapolation to zero heating/cooling rate. Considerable difference between melting point (during heating) and solidification temperature (during cooling) were noticed on cooling/heating curves. The alloy specific heat has also been calculated.

Abstract: Majority structural elements from magnesium alloys are produced by means of casting. The big and complicated elements are mainly sand cast. The aim of the research was to investigate the influence of wall thickness on the castability and microstructure of modern magnesium alloy with RE and Ag additions – QE22. Eight 145x98mm plates have been cast for the research. Their designed thickness was equal: 0.5mm, 1mm, 1.5mm, 2mm, 3mm, 4mm, 5mm as well as 6mm. The parameters of microstructure constituents in each cast has been estimated quantitatively. The critical wall thickness, at which liquid alloy fill the mould cavity completely, is equal 4mm. With decreasing wall thickness, percentage of filled cavity is decreasing linearly. Mean area of grain flat section increased 7 times in the thickest plate (from 501μm² to 3773μm²). The volume fraction of eutectics as well as alloy hardness decreased in the thickest plate.

Abstract: Magnesium and its alloys may be applied as cathodic protection for steel constructions. As the protectors work in water environment, one of the main degradation factors is cavitation erosion. The paper presents results of research on the cavitation erosion of magnesium casting alloy – Elektron 21. The cavitation erosion tests were performed using vibratory apparatus. After the cavitation tests eroded surface and the cross-sections of the specimens were observed by means of scanning electron microscopy. Elektron 21 did not exhibit distinct incubation period of cavitation erosion. The cavitation pits are observed mainly in the α-Mg solid solution grains and on the interfaces between intermetallic phases and the α-Mg. On the other hand, the Mg₃(Nd, Gd) eutectic phases are more resistant to cavitation erosion than α-Mg. They are protecting the solid solution from degradation. However, due to their high hardness they undergo cracking and detachment of from the surface. After longer times of cavitation tests, cracks begin to propagate into the material, which leads to crushing of bigger parts of the material.

Abstract: The complex microstructure of as-cast AlSi7Mg alloy has been investigated. Microstructure observations were done using light microscopy, scanning electron microscopy and transmission electron microscopy. Chemical composition of the microstructure constituents was investigated by means of energy dispersive spectrometry, conducted both during SEM and STEM investigations. Selected area diffraction was used to identify the phases in the alloy. Microstructure of the alloy in the as-cast condition consists of Al-Si eutectic and intermetallic phases in the interdendritic regions. These are: Mg₂Si, α-AlFeMnS, β-AlFeSi and π-AlFeSiMg phases. What is more, number of fine precipitates were found within the α-Al dendrites. Only the occurrence of U1 (MgAl₂Si₂) phase has been confirmed.

Abstract:

Magnesium alloys are widely used mainly in automotive and aerospace industries. There is quite a lot of information about corrosion of the magnesium alloys in available literature. However, the publications concern mainly Mg-Al alloys, while there is a lack of information about Mg-RE-Zr alloys. The following paper presents results of the investigations on the electrochemical corrosion of magnesium casting alloys containing rare earth elements (WE43, WE54, EV31A-Elektron 21) as well as pure magnesium. The alloys were investigated by immersion test in 3.5% NaCl for times up to 7 days. Electrochemical investigations were carried out at ambient temperature in aerated NaCl solution, using potentiodynamic polarization method. It has been shown that the best corrosion resistance is exhibited by alloys with yttrium addition (WE43, WE54), while the weakest by pure magnesium. EV31A alloy exhibits the highest corrosion rate during the immersion test, while WE54 and WE43 alloys had a similar corrosion behavior.

Abstract: The researches have concerned cavitation erosion of AlSi7Mg and AlSi11Mg aluminium casting alloys. The alloys have been investigated in the as-cast condition and after the precipitation hardening. The cavitation erosion tests were performed using vibratory cavitation erosion equipment in 5 minutes. Resistance to cavitation of tested materials was estimated by means of MDE (mean depth of erosion) parameter according to ASTM G32. After the cavitation tests eroded surface of the specimens has been observed by means of scanning electron microscopy. The roughness of the surface was measured on profile contact tester. The best resistance for cavitation erosion exhibited AlSi7Mg alloy after heat treatment, the weakest AlSi11Mg alloy in as-cast condition.

Abstract: The creep resistance of Elektron 21 magnesium alloy containing Zn, Nd, Gd and Zr has been investigated. Test has been conducted at 200°C, 225°C and 250°C with constant load amounts to 90, 120 and 150 MPa up to 100 hours. Some specimens cracked during the test. Metallographic and fractographic research has been performed in order to identify the microstructural changes occurring during the creep resistance test. Microstructure has been observed with light microscopy and scanning electron microscopy. Chemical composition of microstructural components has been investigated with energy dispersion spectroscopy. Research revealed presence of voids, microcracks and inclusions which can significantly influence creep resistance of material.

Abstract: Non-metallic inclusions in Elektron 21 and WE43 magnesium alloys have been investigated by means of scanning electron microscopy. Investigations were conducted both on the fracture surfaces and microsections. Researches revealed presence of alloying elements oxides, inclusions originating in mould material and inclusions originating in the fluxes covering liquid metal surface in the cruicible. The number of inclusions is reduced by application of complex gating system and by leaving small amount of alloy in the cruicible after the pouring process.