Roping is a common surface defect of aluminum alloy sheets for the outer panel, which seriously reduces the visual appearance of automotive and is unacceptable for consumers. Some studies on roping have been carried out, but the effect of hot roughing mill microstructures is rarely reported. In the present work, the effects of two kinds of hot roughing mill grain structures on the roping in AA6014 T4P sheet were investigated by optical microscopy, SEM-EBSD, and roping test.

A hot roughing mill plate with coarse grains and a large volume fraction of the cube texture component (plate A) was prepared. Following the hot finish rolling, primary cold rolling, intermediate annealing, secondary cold rolling, solute solution, and pre-aging, a T4P temper sheet (sheet A) was prepared. The roping in sheet A was obvious. In contrast, the other T4P temper sheet B, prepared with the same procedure as the other hot roughing mill plate with fine grains and less cube texture component (Plate B), showed weaker roping.

The EBSD analysis on the T4P temper sheets displayed that in sheet A the Cube-oriented grains align band-like along the rolling direction. These bands were distributed along the transverse direction of the sheet periodically. While for sheet B, the fraction of the Cube texture component was less than the counterpart, and the corresponding grains were distributed randomly.

The severe roping in sheet A could be explained as follows. After hot and cold rolling, the coarse hot roughing mill grains were deformed to elongated fibers, which were distributed periodically. During the solute solution, the Cube-oriented grains nucleated and grew at the elongated grain boundaries and the transition bands, forming Cube bands distributed periodically like the original fibers.