THE EFFECT OF {10(1)over-bar1}-{10(1)over-bar2} DOUBLE TWINNING ON THE MICROSTRUCTURE, TEXTURE AND MECHANICAL PROPERTIES OF AZ31 MAGNESIUM ALLOY SHEET DURING ROLLING DEFORMATION

{10 (1) over bar1}-{10 (1) over bar2} double twin is the most common twin type being observed in the rolled AZ31 magnesium alloy, especially at low or moderate rolling temperature. Four types of rolled AZ31 magnesium alloy sheets were produced by rolling strong basal textured AZ31 plates at 150 degrees C and 300 degrees C respectively through different rolling paths by two passes till total reduction 17%. The rolling paths are normal and cross rolling respectively: the rolling directions of the two passes for normal rolling are mentally paralleled while perpendicular to each other for the cross rolling. Sheets are characterized in terms of microstructure and texture using optical microscope and scanning-electron microscope equipped with EBSD detector, and their mechanical performances are measured by uni-axial tensile tests at room temperature and a strain rate of 0.001 s(-1). Tensile samples are cut parallel or perpendicular to the final rolling direction to obtain the mechanical anisotropies. The effects of the {10 (1) over bar1}-{10 (1) over bar2} double twins occurred during rolling on the microstructure, texture and mechanical properties of the rolled sheets are discussed and related to each other. The results show that the fraction of {10 (1) over bar1}-{10 (1) over bar2} double twins varies widely in different rolled sheets, which are determined by the rolling temperature. The twins in different rolled sheets are arranged in different ways. In the normal rolled sheets, the traces of twins are approximately perpendicular to the final rolling direction, while in the cross rolled sheets there are both traces of twins parallel and to the final directions. This phenomenon is related to the variant selection of twinning during rolling deformation. And the variant selection law is related to the rolling direction. For the same reason, the textures of twins in the rolled sheets produced through different paths are different. The textures of twins will add onto the bulks, and increases the textural difference between the bulks. The differences between mechanical properties of the rolled sheets are also related to the different textures and microstructures of the sheets caused by twins.