Abstract
Providing a good balance between lightweight and high mechanical properties, the aluminum-based metal matrix composites (MMC) became an interesting alternative for specific industrial applications. However, considering an Al-Mg-Si alloy with a high silicon excess, the ceramic particles added as reinforcement can act on : i) the precipitation kinetics of the coherent and semi-coherent phases, ii) the precipitation sequence of the alloy and iii) the loss of mechanical strength from a peak-aged microstructure obtained by a T6 condition. In order to understand the influence of reinforcement on these aspects, the composite was characterized during isothermal ageing between 100°C and 350°C, allowing us to propose an experimental Isothermal Transformation Curve. Compared to the unreinforced alloy, heterogeneous precipitation of disordered semi-coherent phases occurs on dislocations and the precipitation kinetics were found to be accelerated in the composite leading to an acceleration of the loss of strength from the T6 state, due to the precipitation of the Type-C phase. A study performed on a deformed alloy, demonstrated that the most of the differences observed between the unreinforced alloy and the composite can be explained by the high dislocation density generated in the matrix of the composite due to the presence of ceramic particles. Finally, the JMAK approach turned out to be a powerful tool to model the decrease in mechanical strength occurring during isothermal treatments from T6 state.
Highlights
The aluminum-based metal matrix composites (MMC) have been developed for specific applications such as aerospace, aeronautic and automotive fields [1,2]
For more precise information, such as the crystallography and nature of precipitates the samples were characterized by High Resolution - Transmission Electron Microscopy (TEM) (HR-TEM)
The aim of this study was to understand how the ceramic particles act on the matrix microstructure during isothermal ageing and the consequences on mechanical properties considering an Al-Mg-Si alloy with silicon excess
Summary
The aluminum-based metal matrix composites (MMC) have been developed for specific applications such as aerospace, aeronautic and automotive fields [1,2]. The addition of ceramic particles to Al-Mg-Si alloys is a successful method to achieve a good combination between lightweight, high mechanical properties at elevated temperatures and good conductivity properties. The silicon excess increases the maximum mechanical strength reached after a T6 treatment (8 hours at 170 °C) [3,4]. Both the addition of silicon excess and ceramic particles affect the precipitation sequence and its kinetics during artificial ageing. The study of the impact of these two factors on microstructural modifications during ageing has a particular interest for industrial applications since it can lead to changes of mechanical properties during the use of the materials
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