Severe plastic deformation of the magnesium alloy AZ31

Abstract

Although light weight constructions are an important issue in the automobile and aerospace industry, extruded magnesium profiles are not used in serial production cars. This is mainly due to the fact that magnesium profiles show a strong strength differential effect (SDE) which means the yield point under compressive load is much lower than that under tensile load. This effect is caused by a combination of texture, which is induced by the extrusion process, and twinning. Therefore, this paper deals with the modification of the extrusion process in order to control the texture so that the mechanical properties are optimized for the occurring load. Two different methods were used in this research to improve the mechanical properties under compressive load. One is the Equal Channel Angular Extrusion (ECAE). By using ECAE the extruded specimen is under severe shearing deformation without any changes of its geometrical dimensions. The ECAE process was modified to a linear multiple shearing process. Thereby the material flow is determined by the geometry of the shearing channel. By the use of a modified shearing die multiple shearing during one deformation step was possible. The other method that was used for the severe plastic deformation is called reciprocating extrusion. The material is extruded through a die so that in the first step a reduction of the cross-section occurs. After leaving the extrusion channel the material is upset by a countervailing stem to its original diameter. In this process the shearing of the material occurs in the region of the diminution. Both processes were carried out on as-cast and already indirectly extruded samples of magnesium alloy AZ31. All samples were then tested for their mechanical properties.