QUENCH SENSITIVITY AND TENSILE PROPERTY INHOMOGENEITY IN 7010 FORGINGS

7xxx (Al-Zn-Mg-Cu) alloys develop their strength, through the controlled decomposition (ageing) of a supersaturated solid solution to produce a precipitation hardened microstructure. The supersaturated solid solution is normally produced by water quenching from the solution heat treatment temperature. The kinetics of phase transformations occurring during cooling from the solution heat treatment temperature are limited at small undercoolings by the small chemical free energy, and as the undercooling increases, by reduced rates of substitutional solid state diffusion. This gives rise to the characteristic C shape of time-temperature-property (TTP) curves. The TTP curve for 7010 has been evaluated by a interrupted quench method into a salt bath at temperatures ranging from 450 to 210°C. A TTP curve for 7050T76 sheet data has then been used to predict tensile property inhomogeneity in large 7010 forgings with known cooling rates