Papers by Author: G.I. Rosen

Abstract: One of the most challenging activities for magnesium industry is to increase productivity by introducing cost-effective processes. While die-cast magnesium alloys are in worldwide use, even in the demanding sector of automotive industry, where cost is the major asset, wrought magnesium alloys still not widely available. The aim of the present study was to evaluate the high temperature response by torsion testing of a ZM21 alloy, to calculate the constitutive equations to be used in FEM simulation of the extrusion process. The ZM21 alloy that was considered in the present study was Direct-Chill casted by Alubin Ltd., Israel. Torsion tests were carried out in air on a computer-controlled torsion machine, under strain rates ranging from 10-2 to 5 s-1 and temperatures from 200 to 400°C. The equivalent peak flow stress was related to temperature and strain rate by means of the conventional power-law and by the sinh equation. The microstructure of the alloy, even at 300°C, appeared largely unrecrystallized, with elongated grains; also at 400°C, the structure is more equiaxed, but elongated structures still appears.

Abstract: Technological barriers that relate to limited capability of magnesium extrusion technology still exist, especially for the higher alloyed grades. Part of this is associated with the unfavorable crystallographic structure of the magnesium, which is Hexagonal Close Packed (HCP). This work suggests an innovative and novel technology for reducing the production cycle from cast to finished product. A unique Semi-Solid casting system was designed and constructed in order to enable casting of large scale commercial billets having thixotropic properties. These have been further hot extruded via conventional direct extrusion press. It is shown that all essential parameters have improved significantly. These include extrusion temperature reduction (up to 1500C), press pressure reduction, increase of extrusion rate (up to four times), and, enhancement of surface quality. In addition good mechanical properties and corrosion resistance were achieved.

Abstract: The aim of this project is to develop magnesium alloys extrusion technology for large profiles for application in the automotive industry. In particular it is expected to significantly reduce chassis weight, thus leading to fuel consumption reduction and enhancement of performance of the cars produced by the end user. The entire process required for magnesium alloys extrusion of automobile chassis will be addressed as a first attempt of large magnesium profile extrusion. The challenge of large magnesium profile extrusion (outer diameter up to 10") has never been addressed due to technological barriers that relate to limited capability of magnesium extrusion technology. However, these barriers can be overcome if one has control over the starting material. Since the final performance of the finished product depends on the original microstructure formed over Direct Chill (DC) casting, homogenization, extrusion and subsequent heat treatment, no processing step can be isolated from the other. The R&D activities will focus on alloy selection, production of large magnesium billets, die design, heat treatment and extrusion parameters. These will be accompanied by an economic assessment of the new technology and additional applications.