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

TTP and TTT diagrams of 1424 ahoy (system Al-Li-Mg-Sc-Zr) within temperature interval for quench sensitivity 100-450 degrees C and temperature interval for ageing 100-250 degrees 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 Y, UTS and YS changes criteria is equal to similar to 2 degrees C s(-1). At temperature interval 200-350 degrees C Y, UTS and YS were changed with peak near 275-300 degrees C (temperature of the minimal stability) after the endurance 1-4 min. TTT diagram showed, that the solid solution decomposition with precipitation of S-1-phase (Al2MgLi) in temperature range 250-300 degrees C begins with minimal used duration (15 s), the critical rate of cooling necessary to suppress S-1 phase precipitation has to be > 12 degrees C s(-1). In temperature interval 150-175 degrees C Y, UTS and YS have a second peak after the endurance more than 8 min. At that interval delta'-phase precipitates were found. For ageing temperature interval the peak strength after ageing was found at 150-175 degrees C during 16-32 h. Time-temperature regions of GP zones, ordered solid solutions domains, S-1'(S-1) phases existence were established. (C) 2000 Elsevier Science S.A. All rights reserved.