Composites are a group of materials that consist of at least two materials that differ in physical and chemical properties. Aluminium matrix composites are popular lightweight materials due to their favorable properties, such as excellent castability, high specific strength and stiffness, high wear resistance, and good elevated temperature properties. They can be produced using simple casting processes that ensure lower manufacturing costs. In "in situ" composite manufacturing, a chemical reaction occurs during the manufacturing process that causes the formation of reinforcing phases, such as Mg2Si, in the aluminium matrix. The Al-Mg2Si composite is an ultra-light material, and due to the many excellent properties of the Mg2Si reinforcement, it is widely used today in structural applications and the automotive industry. Mg2Si reinforcements, which can agglomerate after casting in the aluminum matrix, are often rough and irregular in shape, and other inhomogeneities also appear in the microstructure. As a result, the mechanical properties of the composite can be significantly worse. The properties can be improved by homogenization annealing at 540 °C, during which, through diffusion processes, low-melting eutectics and crystalline precipitates are eliminated, the shape of intermetallic phases is changed, and the formation of uniformly distributed, fine, hardening precipitates is enabled.
The purpose of the master's thesis was to follow the homogenization treatment of the Al-Mg2Si composite at 540 °C using measurements of electrical resistivity and res scanning calorimetry (DSC). The isopleth phase diagram and Scheil diagram of non-equilibrium solidification were calculated using Thermo-Calc software. This process was followed by casting and preparing samples to measure electrical resistivity and differential scanning calorimetry. DSC heating and cooling curves were made, and solidification and melting temperatures of individual phases were determined. After the measurements, we conducted a metallographic examination to track microstructural changes during the homogenization process.
The measurements of the electrical resistivity showed that after 24 h of annealing at 540 °C, the homogenization processes had not yet fully completed. The DSC curves do not show much similarity to the electrical resistivity curves. The electrical resistivity curves drop throughout the process, while the DSC curves show a marked drop after 17 h, followed by a rise in value until the end of annealing. Optical and scanning electron microscopy confirmed the presence of microstructural components expected according to thermodynamic calculation in the examined composite, and the results of point and line EDS analysis also confirmed the presence of a ternary eutectic (αAl+βSi+Mg2Si).
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