Papers by Author: Daniel Larouche

Abstract: Utilization of aluminium-lithium alloys in aerospace applications requires an understanding of how processing and product geometry impact their microstructure, crystallographic texture and mechanical properties. In this paper, the effect of various microstructural features as well as deformation textures on the static mechanical properties of Al-Li extruded components has been investigated. These relationships are discussed with regard to two 2099-T83 extruded sections, i.e. a cylindrical extrusion and an integrally stiffened panel (ISP). The ISP typically shows an unrecrystallized microstructure with varying texture depending on the location along its cross section while the cylindrical extrusions present a strong fibre texture. The anisotropy is noticeable in tensile and compressive tests for both types of extrusions.

Abstract: An integrally stiffened panel (ISP) made from extruded 2099-T83 Al-Li alloy was subjected to fatigue loadings to investigate the influence of both the local texture and grain structure on fatigue crack propagation (FCP) behavior. The microstructure was mainly unrecrystallized. Grains were mostly layered in the web and fibrous in the other locations. Fiber texture components were present in the stiffener locations, and a rolling-type texture in the web. Resistance to FCP decreases as the local aspect ratio increases. Changes in FCP rates in the web, stiffener base and stiffener web were consistent with the microstructural features and texture. The stiffener cap with a strong fiber texture similar to that of the stiffener base exhibited a lower resistance to FCP, suggesting that the influence of the texture is convoluted in the stiffener cap by the markedly different grain structure. Therefore, FCP behavior in this alloy appears to be governed by both texture and grain structure.

Abstract: The aerospace industry strives to develop materials allowing an increase in payload and reducing fuel consumption. Al-Li alloys, with their low density and high strength are currently in use for such applications and have potential for additional applications. When compared to composites, utilizing Al-Li alloy products is cost effective for aerospace companies as they do not need to redesign pre-existing fabrication facilities. The joining of these alloys by conventional methods is limited by segregation of alloying elements and the formation of oxides during high temperature exposure. This study focuses on solid state joining method that has the potential to generate low heat and be defect free - Friction Stir Welding (FSW). AA2199 sheets were joined by FSW. Process variables included table force, tool rotation speed and weld travel speed. A post weld heat treatment (PWHT) was applied to improve the mechanical properties by precipitation of strengthening phases. An increase in hardness of the weld zone from 95HV to 125HV upon PWHT was recorded for selected welding conditions. The type and morphology of second phase precipitates is deemed responsible for this effect. It is suggested that the high temperature and high strain levels characteristic of welds with fast tool rotation allow for the dissolution of precipitates during welding. The re-precipitation of these second phases during PWHT allowed the welds to recover strength to the level of the base material.

Abstract: In the past 3 years, Pyrotek in association with Laval University and the Industrial Materials Institute of the National Research Council of Canada has developed a simulation package proposing a unique approach in the fluid flow calculation of molten aluminum distribution with a combo bag in the ingot head of sheet casting. This paper will summarize the difficulties encountered and the solutions that were adopted to render that simulation tool efficient and consistent. Validation of the model using actual casting tests will be detailed as well as the major change in the simulation package in order to obtain decent calculation times. Some examples of simulations will be given to demonstrate that the initial goal of this project has been achieved by the development of a mathematical simulation tool to design and improve metal distributors used in the sheet casting production.