Solid State Phenomena Vol. 191

Abstract: AMCs due to good thermal and tribological properties, they are applied as the material for: pistons in modern combustion engines, drive shafts, shock absorber cylinders and brake nodes. Heavy-duty operation, especially under tribological conditions, frequently in corrosive environment, requires knowledge on their corrosion resistance. This paper presents the initial results of the research on susceptibility of aluminium alloy matrix composite material reinforced by SiC particles and mixture of SiC+C particles to corrosion. The purpose of the research was to determine the influence of reinforcing phases, their type and shape on corrosion behaviour in a typical corrosion environment, with low NaCl concentration, in relation to the matrix alloy. Determination of corrosion resistance of Al/SiC+C hybrid composite is a new issue and falls within the field of interest of the authors of this article.

Abstract: The aim of the paper is to present the possibilities of computational simulations for the casting of aluminum matrix composite (AlMMC) reinforced with ceramics based on experimental data. The comparison of simulation and experimental results concerned the solidification process i.e. the course of solidification, temperature distribution and final arrangement of reinforcement particles. First, we have performed the experimental gravity casting of the aluminum matrix alloy AK12 (AlSi12CuNiMg2) and the composites AK12/SiC and AK12/C_g reinforced with silicon carbide SiC and glass carbon Cg, respectively, into the sand mold. During the experiment we have recorded the temperature using the ThermaCAM photometer system as well as in the selected point inside the sand mold. Using experimental data we have carried out the numerical calculations according to the methods and procedures contained in the program ANSYS Fluent 13. We have based the simulations on the two-dimensional model in which the Volume of Fluid (VOF) and enthalpy methods have been applied. The former is to describe two-phase system (air-composite matrix free surface, volume fraction of particular continuous phase) and the latter shows modeling of the solidification process of the alloy and composite matrix. We have used the Discrete Phase Model (DPM) to depict the presence of reinforcement particles. The assumption of the appropriate values of simulation parameters has shown that the simulation results are convergent with experimental ones. We have observed a similar course of the composite solidification (temperature change at the designated point), the temperature distribution and the arrangement of reinforcement particles for the simulation and experiment.

Abstract: The article presents the results of tests connected with the influence of strain parameters on the change of flow stress and microstructure of magnesium alloy AZ61 (symbol according to ASTM norms). Test of uniaxial hot compression were conducted in temperature range from 250 to 400°C and the strain speed from 0.01 to 1 s-1. Analysis of plastometric tests and microstructure observation allowed to establish which mechanism - slip or twinning – is dominant in particular conditions of shaping AZ61 alloy. Achieved results were compared with previous results achieved for AZ31 alloy type with lower content of aluminium.

Abstract: Magnesium alloys are the lightest, widely used structural material. They are often used in aeronautical and automotive industries, where the weight savings are essential. Magnesium alloys present acceptable mechanical properties but their high temperature properties are unsatisfactory. This led to development of magnesium alloys with rare earth elements addition. To achieve good mechanical properties these alloys are modified with zirconium. Modification affects positively also corrosion resistance of Mg-RE alloys. It is important to study impact of modifier amount on the structure and properties of these alloys. Unmodified and modified alloys were investigated. Three variants of modification were: modification according to Magnesium-Elektron specification, 50% and 100% more modifier. Mechanical and structural properties were investigated. Fractures were observed on scanning electron microscope. Results showed that grain refinement and yield strength increase with increasing amount of modifier. Impact of modification on tensile strength is unclear, probably because of non-metallic inclusions in the material’s structure. The inclusions sources are oxygenated nappe of liquid metal and fluxes, used during smelting.

Abstract: Magnesium alloys are the lightest, widely used structural material. They are often used in aeronautical and automotive industries, where the weight savings are essential. Due to high responsibility of the elements made from magnesium alloys it is important to achieve high quality castings without any defects. The paper presents results of investigations on impact of sand mould cooling rate on microstructure and quality of the castings. Six identical castings, fed and cooled in different ways were investigated. Studies consisted of: RTG investigations and SEM and LM observations. Microstructure was evaluated qualitatively and quantitatively. RTG investigations showed that casting without feeder and cooler, casting only with feeder and castings cooled with 20mm and 40mm thick cooler contains voids inside. Castings with feeder and coolers 20mm and 400mm thick were flawless. Microstructure evaluation showed that castings with and without defects have different structure. Castings with defects were characterized by higher volume fraction of Mg17Al12 intermetallic phase. Flawless castings were characterized by fully divorced eutectic.

Abstract: Magnesium alloys, thanks to their low density, are characterized by very high specific strength and specific stiffness. Due to acceptable mechanical properties, these alloys are widely used in automotive and aerospace industries for the elements such as: gearbox and engine housings, steering wheel columns or wheels. The main problem of the most common magnesium alloys – such as AZ91 are their weak high temperature properties. This led to development of alloys containing rare earth elements. These alloys achieve their demanded mechanical properties after grain refinement with the zirconium. Because of a big responsibility of the elements made from Mg-RE alloys, it is important to investigate modification impact on properties of the magnesium alloys. The paper presents results of studies properties of the WE43 and Elektron 21 casting magnesium alloys, modified in three different ways – according to Magnesium-Elektron specification, 50% stronger modification and 100% stronger. For the comparison, unmodified alloys were also investigated. Investigations showed, that alloys modified according to MEL specification presents optimal set of structural and mechanical properties. Further increase of amount of modifiers doesn’t let to significant increase of mechanical properties. Fractographic investigations showed many non-metallic inclusions on the fractures surface, which are result of faulty smelting process.

Abstract: In this article, the impact of long-term annealing on transformation of microstructure, in sand casting and die-casting Mg-5Al magnesium alloy was discussed. The Mg₁₇Al₁₂ phase of the diverse morphology is the basic strengthening phase in Mg-5Al alloys. After sand casting microstructure of Mg-5Al alloy consists of α-Mg solid solution with continuous and discontinuous precipitates of Mg₁₇Al₁₂ phase. After die-casting, the structure is characterized by significant grain refining of α-Mg solid solution, however Mg₁₇Al₁₂ phase, together with α-Mg solid solution, forms fully divorced eutectic. The Mg₁₇Al₁₂ phase undergo decomposition and coagulation at the temperature above 180°C and higher.

Abstract: Magnesium alloys are widely used in automotive and aerospace industries due to their great connection of low density and good mechanical properties. They are also characterized by good castability and weldability. Their weak high temperature properties and corrosion resistance, led to development of magnesium alloys containing rare earth elements. Casting is the most popular way of manufacturing magnesium elements. However, there is a lack of investigations concerning impact of different factors on fluidity of these alloys. This paper presents results of investigations on influence of pouring temperature on castability and microstructure of QE22 and RZ5 magnesium alloys. In case of QE22 alloy, the filling length of the liquid alloy increased with the increasing pouring temperature. In RZ5 no such dependence was noted. This is probably caused by oxide films in the structure of material. Grain refinement and eutectics volume fraction also didn’t present correlation with pouring temperature.

Abstract: The paper presents analysis of section thickness’ influence on microstructure of Elektron 21 and QE22 magnesium alloys in the form of a stepped casting test. Solid solution grain size and volume fraction of eutectic areas were measured using light microscope and sterological methods. The results showed the significant increase of grain size caused by wall thickness and its slight decrease connected with the distance beetwen analysed section and the gating system. This relationship was confirmed using statistical methods. QE22 alloy demonstrated finer grain structure than Elektron 21 alloy as well as lesser susceptibility of grain size to solidification conditions

Abstract: The paper presents results of microstructural investigations and creep properties of Mg-5Al-3Ca-0.7Sr-0.2Mn (ACJM53) and Mg-5Al-3Ca-0.8Sn-0.7Sr-0.2Mn (ACTJM531) magnesium alloys in as cast condition. The microstructure of the ACJM53 consists of α-Mg, (Mg,Al)₂Ca - C36, Al₃Mg₁₃(Sr,Ca), Al₂Ca - C15 and Al_xMn_y. Additionally, the CaMgSn phase is observed in the ACTJM531 magnesium alloy. The addition of 0.8 wt% tin reduces the tensile strength at ambient temperature and creep resistance at 180°C.