Deformation Mechanisms of Superplastic Al-Li 8090 Alloy Examined by X-Ray Texture Measurements

Abstract

The texture evolution of the Al-Li alloy 8090 has been investigated in order to analyze the microscopic mechanisms operative during deformation under different conditions of temperature and strain rate. A through-thickness texture gradient is present in the as-received material. As will be seen, the predominant deformation mechanisms are different in the mid layer and in the outer regions of the 8090 sheet alloy. In the outer regions, the texture intensity decreases with deformation and no significant changes in the main components were observed, indicating the predominance of grain boundary sliding (GBS). In the mid-layer, however, texture sharpens with straining and major changes in the main texture components were detected, revealing that crystallographic slip (CS) plays an important role in the deformation of this zone. CS takes place mainly in two slip systems and causes the orientations to move along the .BETA.-fiber in Euler space, towards the Copper component in longitudinal tests and towards the Brass component in transverse tests. The comparably small ductility of the 8090 alloy, with respect to other similar superplastic aluminum alloys, may be due to the operation of CS in the mid-layer.