Impact of hot rolling on the r-values of 6000 series aluminium alloys

Crystallographic texture of sheet metal influences formability significantly. Lankford coefficient or the so-called r-value, a texture related property, is a property often specified as a customer requirement and therefore a property that requires close monitoring and control during the production process. Through systematic experiments, it is demonstrated how hot rolling, especially hot tandem rolling influences r-values of wrought aluminium alloys. A tandem rolling model has been developed that enables control of final r-value for a given 6016 alloy with a given downstream process. The model clearly shows how entry temperature and exit speed of tandem mill can be used to control the final product’s r-value. The model that provides a metallurgical explanation for the effect, can be used to steer the tandem mill in such a manner that a minimum r-value is guaranteed and at the same time, variations of r-value along the length of the strip are minimized or suppressed. The model also provides a better alternative to the existing and conventional tandem mill steering methodology based on constant exit temperature. The proposed methodology is based on keeping a (nearly) constant Zener-Hollomon parameter along the length of the strip during tandem rolling.