Quench sensitivity and its effects on mechanical properties of 8090 Al-Li superplastic sheets

Quench sensitivity of the superplastic 8090 Al-Li thin sheets was investigated from the strengthening point of view of the various precipitates formed in the alloy. Specimens subjected to different cooling rates (water quenching, silicon oil cooling or air cooling) from solution treatment (or superplastic forming) temperature were examined by tensile testing, transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). Experimental results show that delta' is the predominating phase in the alloy under all cooling conditions. Since delta' could be formed in a similar amount and size after the T6 treatment and since the amount of S' precipitates and T-2 particles were extremely low, the superplastic 8090 Al-Li alloy would thus always exhibit low quench sensitivity.