Wrought Magnesium Components for Automotive Chassis Applications 2011-01-0077

Automotive structural components are exposed to high loads, impact situations and corrosion. In addition, there may be temperature excursions that introduce creep as well as reduced modulus (stiffness). These issues have limited the use of light metals in automotive structural applications primarily to aluminum alloys, and primarily to cast wheels and knuckles (only a few of which are forged), cast brake calipers, and cast control arms. This paper reports on research performed at Chongqing University, Chongqing China, under the auspices of General Motors engineering and directed by the first author, to develop a protocol that uses wrought magnesium in control arms. The goal was to produce a chassis part that could provide the same engineering function as current cast aluminum applications; and since magnesium is 33% less dense than aluminum, would be lighter. The paper documents the vehicle requirements for one particular component, a front upper control arm (FUCA) and how an alloy and processing were selected that meets vehicle requirements. A unique processing route was developed that included: alloy selection → producing a cast billet of the alloy → extrusion (to eliminate porosity) → forging (to get a more homogeneous structure), and → heat treatment (to stabilize the structure). Property data will be presented that show the effectiveness of this protocol to produce a magnesium FUCA that has sufficient tensile yield strength, ductility and stiffness to compete with the current aluminum part. Because of the global turmoil after the project was started, the team was unable to complete a vehicle demonstration but was able to produce test samples that demonstrated the potential for the application.