22 JOM • May 2004 Magnesium Overview Consumption of wrought magnesium products was reduced by half between 1971 and the 1990s. To increase the use of wrought magnesium, several chal- lenges must be overcome: its formability at room temperature is lower than steel or aluminum; its productivity is lower than steel or aluminum; and extruded magnesium exhibits a marked anisotropy of yield when comparing tension and compression. This article describes research on the rapid evaluation of the extrusion behavior of wrought magne- sium alloys. The work aims to establish a methodology for rapid prototyping of alloys and to assess the effects of aluminum on the behavior of AZ-series magnesium alloys. INTRODUCTION Wrought magnesium alloys were first used in large amounts during the 1930s, when extruded, rolled, and forged alloys were used in aircraft engines and armaments. The average monthly production of magnesium sheet (princi- pally AM503) in Germany peaked at 300 t in 1942. 1 At the same time, Dow in Expanding the Extrusion Limits of Wrought Magnesium Alloys Chris Davies and Matthew Barnett the United States was extruding water heater anodes and fabricating magne- sium truck bodies, and Magnesium Elektron Ltd. was supplying slab and billet to secondary fabricators. 1 After World War II, Dow continued to produce a wide range of products, as exemplified in the company’s technical sales litera- ture from the time. 2,3 Aircraft were prime users of wrought alloy: the B-36 bomber—which entered service in 1949 and was withdrawn in 1959—contained approximately 3.4 t of magnesium alloy sheet, and 5.2 t combined of castings, extrusions, and forgings. A dramatic rapid price increase resulting from increased energy costs coupled with increasing toughness of aluminum alloys led to a decrease in total magnesium consumption. Consumption of wrought products declined from around 10,000 t per annum in 1971 to about half that in the 1990s. The current demand for wrought magnesium is restricted to specialty components such as photoen- graving plates, sporting goods, and electrochemical uses such as extruded anodes. The growth outlook for structural Ram Support Heating Element Container Billet Die Insulation wrought magnesium alloy has typically been predicted to be flat 4,5 or modest. However, with the advent of Corporate Average Fuel Economy legislation setting fuel economy targets in the United States and the European Union, there is an opportunity for the lightweighting of motor vehicle components as long as certain technical challenges to magne- sium alloy use can be overcome. MAGNESIUM FORMABILITY The increased use of wrought magne- sium faces several technical challenges: its formability at room temperature is lower than steel or aluminum (both for sheet and extrudate); its productivity is lower than steel or aluminum; and extruded magnesium exhibits a marked anisotropy of yield when comparing tension and compression: the tensile yield stress may be as much as twice the compressive yield stress, and such behavior has to be incorporated into the design of components or eliminated. Current wrought magnesium alloys must be formed at elevated temperatures because of the limits imposed by their Figure 1. Limit diagrams constructed for some common aluminum and magnesium alloys. Figure 2. A sche- matic of the labo- ratory extrusion press.