Formability of AA6061 alloy sheets in warm forming temperature range

Significant improvement in formability of aluminum alloys can be obtained when these materials are formed in the warm working temperature range (below recrystallization temperature). In the present work, an experimental set up is designed and developed to determine formability of Al–Mg–Si alloy (AA 6061) sheets of different thickness in the temperature range of 200–300 ℃. It consists of lower and upper dies with casing heaters, a hemispherical bottom punch with heating element, controls for punch displacement and speed of the 60-ton double action hydraulic press used in the experiments. An attempt has been made to experimentally determine the influence of punch speed, temperature, and sheet thickness on the limiting dome height and forming limit diagram in the warm working temperature range. The effect of temperature and strain rate on tensile properties of the alloy has also been studied. The plane strain intercept values of forming limit diagram (FLD 0 which is the major strain value at zero minor strain), determined experimentally at different conditions and thicknesses, have been used to develop a correlation for FLD 0 with temperature, punch speed and thickness. The FLD 0 values obtained from the developed correlation agreed well with the experimental values with the difference less than 10% in most cases. The confirmatory experiments at an intermediate punch speed showed an error of just 8%. The effect of temperature and punch speed on strain distribution in the forming limit diagram samples and the load–displacement curves has also been analyzed.