Toshio Komatsubara

Recrystallization Textures of Al-Mg-Si Alloy Sheets Produced by Symmetric and Asymmetric Combination Rolling

In order to improve deep drawability of 6000 series aluminum alloys for automotive body panels, texture control for increasing r-value of the sheets was attempted by combination of symmetric and asymmetric rolling. Asymmetric warm rolling at relatively low reduction after symmetric rolling made it possible to form TD-rotated β-fiber texture including {111} components. Recrystallization textures of the T4-treated materials varied significantly depending on roll speed ratio and reduction in asymmetric warm rolling. On appropriate rolling conditions, {111}<110> orientation with high r-value was formed as a main component of recrystallization texture. On the other hand, two-stage heat treatment consisting of low temperature annealing and subsequent T4-treatment led to a significant change in recrystallization texture. In the sample annealed for long time at a low temperature, TD-rotated β-fiber rolling texture was retained even after solution treatment at a much higher temperature, because recovery or recrystallization took place to some extent during low temperature annealing.

Increase of Lankford Value of Al-Mg-Si Sheets for Automotive Panel Produced by Asymmetric Warm Rolling

To restrain global warming, weight reduction of autobodies is needed for fuel saving and discharge of carbon dioxide (CO2) gas. Usage of light weight aluminum alloy sheets is efficiency for the weight reduction, but the less formabilities comparing with low carbon steel sheets restrict the usage of autobodies applications actually. To improve the formabilities of aluminum alloy sheets, asymmetric warm rolling is studied. The formability of a metallic sheet strongly depends on the textures. Lankford value (r-value), one of the indicators of formability, of recrystallized low carbon steel sheets is high because the density of {111}//ND orientation suitable for deep drawing is high. The texture of conventionally cold rolled and recrystallized aluminum alloy sheets mainly consists of cube texture which is lower r-value and unsuitable for deep drawing. It is well known that similar texture to low carbon steel sheet can be obtained by shear deformation in aluminum alloy sheets. To provide the shear texture in aluminum alloy sheet, asymmetric warm rolling is carried out at 473K-573K with differential roll velocities. A small amount of {111}//ND orientation which is hardly produced by conventionally cold rolling is observed in asymmetric warm rolled aluminum alloy sheets after recrystallizing. Controlling the asymmetric warm rolling conditions, such as rolling temperature, total reduction and asymmetric ratio, higher r-value and deep drawability comparing with conventionally processed aluminum alloy sheets are achieved. Other properties such as strength, elongation, and bendability of asymmetric warm rolled sheets are almost same as those of conventionally processed sheets.