TTP and TTT diagrams for quench sensitivity and ageing of 1424 alloy

TTP and TTT diagrams of 1424 alloy (system Al–Li–Mg–Sc–Zr) within temperature interval for quench sensitivity 100–450°C and temperature interval for ageing 100–250°C were obtained. Solid solution decomposition kinetics were determined by electroconductivity and tensile properties measurements. Phase transformations have been investigated using by high sensitivity X-ray phase analysis, TEM, EDX and DSC. Cooling rate at quenching enough to suppress solid solution decomposition estimated by ϒ, UTS and YS changes criteria is equal to ∼2°C s−1. At temperature interval 200–350°C ϒ, UTS and YS were changed with peak near 275–300°C (temperature of the minimal stability) after the endurance 1–4 min. TTT diagram showed, that the solid solution decomposition with precipitation of S1-phase (Al2MgLi) in temperature range 250–300°C begins with minimal used duration (15 s), the critical rate of cooling necessary to suppress S1 phase precipitation has to be >12°C s−1. In temperature interval 150–175°C ϒ, UTS and YS have a second peak after the endurance more than 8 min. At that interval δ′-phase precipitates were found. For ageing temperature interval the peak strength after ageing was found at 150–175°C during 16–32 h. Time–temperature regions of GP zones, ordered solid solutions domains, S′1(S1) phases existence were established.