Papers by Author: Tomasz Rzychoń

Abstract: In this paper microstructure and creep properties of Mg-Al-Ca-Sr, Mg-Zn-RE-Zr and Mg-Sn-Si gravity casting magnesium alloys are presented. The microstructure was characterized using light microscopy, scanning and transmission electron microscopy. Phase identification was made by SAED and XRD analysis. Creep tests were carried out in the temperature range from 180°C to 200°C at applied stress of 60 MPa. Microstructure of Mg-Al-Ca-Sr alloys composed of α-Mg grains and C36, C15 and C14 intermetallic compounds in the interdendritic regions. In case of Mg-Zn-RE-Zr alloys the dominant intermetallic compound is (Mg,Zn)₁₂RE phase also located in the interdendritic regions. Microstructure of Mg-Sn-Si alloys after T6 heat treatment consists of plate-like precipitates of Mg₂Sn phase, primary crystals of Mg₂Si phase and globular Mg₂Si phase. Among the alloys in this study, the low-cost Mg-5Al-3Ca-0.7Sr alloy has the best creep resistance. The other alloys, excluding the Mg-5Si-7Sn alloy, are characterized by a poorer creep resistance in compared to Mg-5Al-3Ca-0.7Sr alloy, however their creep resistance is better if compared to typical Mg-Al alloys. Creep resistance of Mg-5Si-7Sn alloy is very low.

Abstract: The microstructure and hardness of as-cast Mg-5Si-7Sn-5Mn alloy after solution and ageing treatments is presented in this paper. It was found that the microstructure of as-cast alloy. is composed of primary dendrites crystals of Mg₂Si phase, α-Mg matrix, long needle-like precipitates of Mn₅Si₃, Chinese script particles of Mg₂Si phase and irregular Mg₂Sn phase. The solution treatment at 500°C causes the dissolution of the Mg₂Sn phase in the α-Mg magnesium solid solution, whereas the remaining intermetallic compounds are stable in this temperature. The hardness of alloy increases from 73 HV2 to 96 HV2 at 250°C. The increase in hardness is a result of the formation of the lath-like precipitates of Mg₂Sn phase within the α-Mg matrix.

Abstract: In the present study, the microstructure of Mg-5Si alloys with tin, aluminum and manganese was investigated. The microstructure of Mg-5Si alloy consists of the primary coarse Mg₂Si phase, α-Mg solid solution and eutectic α-Mg + Mg₂Si in which the eutectic Mg₂Si phase solidifies in the form of Chinese script particles. The Mg₂Sn phase and α-Mg solid solution with tin appear in the microstructure, when 7 wt.% of Sn was added to the Mg-5Si alloy. Aluminum dissolve in the α-Mg matrix and participates in the formation of Al₂Sn phase. The addition of manganese promotes the formation of Mn₅Si₃ compound.

Abstract: The microstructure of Mg-5Si alloy consists of the primary coarse Mg₂Si phase, α-Mg solid solution and eutectic α-Mg + Mg₂Si, in which eutectic Mg₂Si phase solidifies in the form of Chinese script particles. When 0.2 wt.% of Ca was added to the Mg-5Si alloy the size of primary Mg₂Si phase remained unchanged. The modification effect of calcium on the primary Mg₂Si phase was effective only in the Mg-5Si-0.5Ca alloy. The morphology of the primary Mg₂Si phase is changed from the coarse dendrite shape to polyhedral shape and the size of primary crystals is significantly reduced. The addition of 0.6 wt.% Ca to Mg-7Si alloy did not cause the modification of primary Mg₂Si phase.

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: The influence of strontium addition on the microstructure of a Mg-9Al-2Ca alloy was investigated. The microstructure of Mg-9Al-2Ca-xSr alloys consists of α-Mg, (Mg,Al)₂Ca with C15 structure, Al₄Sr and Al_xMn_y phases. The addition of strontium decreases the grain size of the α-Mg phase and decreases the aluminum content dissolved in the α-Mg solid solution. Moreover, the volume fraction of the Al₄Sr phase increases with increasing strontium content. Strontium does not influence on the volume fraction of (Mg,Al)₂Ca phase.

Abstract: Magnesium alloys containing yttrium and neodymium are known to have high specific strength, good creep and corrosion resistance up to 523 K. The addition of ceramic particles strengthens the metal matrix composite resulting in better wear and creep resistance while maintaining good machinability. In the present study, WE43 magnesium matrix composite reinforced with SiC and carbon particulates were fabricated by stir casting. The microstructure of the composite was investigated by optical microscopy, quantitative metallography, scanning electron microscope and XRD analysis. Microstructure characterization of WE43 MMC showed inhomogeneous reinforcement distribution and presence of shrinkage porosity. Reinforcing particles are well bonded with the matrix, however, in some cases thin reaction layers was detected. The presence of SiC particles assisted in improving hardness.

Abstract: The paper presents results of microstructural investigations of Mg-5Al-3Ca-0.7Sr-0.2Mn (ACJM53) magnesium alloys in the as-cast condition and after heat treatment at 450°C for 4.5 hours. Two kinds of transformation were observed in ACJM53 alloy after heat treatment: (Mg,Al)2Ca (C36) → Al2Ca (C15) and Al3Mg13(Sr,Ca) → Mg17(Sr,Ca)2 transformations without the change in morphology of output compounds. Morphology of Mg2Ca (C14) have been changed from fine lamellar to globular and precipitation process of Al2Ca (C15) phase inside the grains of solid solution was found.

Abstract: In this paper the results of microstructural investigations and methodology of detection of intermetallic compounds were reported. The microstructural investigations included the light microscopy, scanning electron microscopy, chemical microanalysis and X-ray diffraction analysis. It was found that the microstructure of Mg-5Al-3Ca-0.7Sr-0.2Mn alloy consists of α-Mg, (Mg,Al)2Ca, Al3Mg13(Sr,Ca), Mg2Ca and Al2Ca intermetallic phases. The correct detection of these phases requires the high magnifications and a large number of measurements fields.

Abstract: The microstructure of Mg-xAl-3Ca-0.8Sr alloys consists of the α-Mg solid solution, irregular-shaped (Al,Mg)₂Ca, bulky Al₃Mg₁₃Sr and lamellar (Al,Mg)₄Sr phases. The results showed that aluminum has a positive effect on the corrosion resistance of Mg-xAl-3Ca-0.8Sr alloys. The main corrosion product is magnesium hydroxide Mg (OH)₂ which forms a cracked layer on the surface of Mg-xAl-3Ca-0.8Sr alloys.