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Étude des mécanismes d’endommagement de la microstructure d’un alliage d’aluminium-silicium pour application automobile à partir d’éprouvette modèle à défaut contrôlé

Abstract : Understanding the impact of the manufacturing defects (porosity, brittle inclusions) resulting from the Lost FoamCasting (LFC) process is a major concern in the cracks development under mechanical stress. The Al-7Si-3Cualloy (A319) will be considered in this crack mechanisms analysis. Generally, samples are obtained by cylinderhead sampling, but the variability in the distribution and characteristics of defects complicates the analysis ofcracking mechanisms. The new approach is to create a model test specimen with a representative cylinder headmicrostructure in terms of constituents and defects. Controlling the defect position allows to know the crack ini-tiation location. Hence, the observation area is limited during the mechanical test and it helps to ease quantitativemeasurement at a very fine scale. Two strategies are considered for the test specimen. The first method consistsin closing pores of the LFC alloy cut from the engine with the Hot Isostatic Pressure (HIP) process and drill aninclined hole in the center of the machined specimen. Instrumented cyclic mechanical tests with cameras wereperformed using a tensile micromachine. The displacement fields around the hole on the surface were measuredand analysed with digital image correlation. The test was stopped at different stages to characterize the 3Dmorphology of the micro-cracks by X-ray microtomography. The von Mises strain field calculated on the surfaceand those calculated in the volume allow an understanding of the damage mechanisms in the region of interestof the specimen. The second method consists in controlling the solidification cooling rate of a tensile sample castin our laboratory’s foundry with the aim of placing an internal pore in the middle of the gauge length. Opticalmicroscopy and X-ray microtomography observations were carried out in order to quantify the microstructurefeatures and the defects location.
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Submitted on : Tuesday, May 24, 2022 - 4:40:25 PM
Last modification on : Wednesday, May 25, 2022 - 3:42:25 AM

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  • HAL Id : tel-03677496, version 1

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Alexis dos Santos. Étude des mécanismes d’endommagement de la microstructure d’un alliage d’aluminium-silicium pour application automobile à partir d’éprouvette modèle à défaut contrôlé. Matériaux. Centrale Lille Institut, 2021. Français. ⟨NNT : 2021CLIL0006⟩. ⟨tel-03677496⟩

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