Papers by Author: Y. Rami

Abstract: The increasing attention to magnesium alloys in extruded profiles, especially in the transportation industry, is related to their low density associated with good mechanical properties and complete recyclability. This allows to push towards both increasing efficiency and pollution restrictions. However, these advantages are negatively balanced by the production rates drop in relation to dangerous profile temperatures increasing that force to keep low velocities. In this context, a novel porthole die has been purposely designed for magnesium alloys allowing an increasing of the process velocity up to four times with respect to past solutions. The mandrel consisted of three ports made by 120° bridges that created an equal number of seam welds. The extruded tubes, made in ZM21, were 50 mm in diameter and 2 mm in thickness and were tested under different process conditions. In the present work, the quality of the seam welds has been investigated in relation to each process condition by means of the rubber plug testing method that allowed to applied an hydrostatic tensile state.

Abstract: The market share of wrought Magnesium products such as structural and functional components is recently increasing. Extrusion at elevated temperatures is used to produce reliable plastic deformation, since magnesium alloys have limited ductility at room temperature. In order to produce sound extruded products, high quality billets are required. Understanding the influence of direct chill casting conditions on the production properties such as quality, safety, workability and microstructure have a profound importance. Comprehensive computer simulations were used in order to model the casting so that process parameters can be identified and controlled, resulting in significant benefits. The aim of modeling is to provide temperature profiles for a more accurate solidification analysis, predict the solidification time and the effect of cooling on the solidification. The experimental study included castings of several Magnesium alloys, each with 7 (seven) thermocouples that were submerged into the billet. Verification of the simulations was carried out based on the data collected. Complimentary work was conducted on microstructure analysis in as cast and as-extruded states.

Abstract: The high temperature response in torsion and creep of two extruded Mg-Zn alloys was investigated in the present study. The alloy 0 (Mg-2Zn-1Mn) was found to exhibit a lower strength than the alloy 2 (Mg-0.55Zn-0.79Mn-0.75Al-0.17Ca), even if the activation energy for creep was similar for both materials (170-180 kJ/mol). The difference in flow stress was here preliminarily attributed to the precipitation of fine Al2Ca particles.