MetalEng--This is what I think about the 18 minutes at 204C.I think the 345MPa and 13% figures are valid, at least to the point that one could pick them off the ageing curve.But, they may not represent actual data points obtained when the ageing curve was run (i.e. you get interpolated data when you pick a point on the curve).And no, I do not think this would be a practical heat treatment.It is a one time result that some researcher got when he ran an ageing experiment.The published heat treatments in the Aluminum Association and Alcoa handbooks have been well validated and tested. If you pick one wild heat treat off a graph, you have no way of knowing what the fatigue properties, SCC properties or residual stress level in the product might be.You only have that one bit of data, i.e. the YS and %E.