Investigation of quench sensitivity of high strength 2219 aluminum alloy by TTP and TTT diagrams

Abstract

The time-temperature-transformation (TTT) curve and time-temperature-property (TTP) curve of 2219 aluminum alloy were determined by an interrupted quench technique. The results show that the quench sensitivity temperature range of 2219 aluminum alloy is from 300 °C to 480 °C and the nose temperature is about 440 °C. The transmission electron microscopy (TEM) observation indicated that, during isothermal holding at 440 °C, a number of coarse equilibrium rod-shaped θ particles precipitated and grew fast, resulting in loss of solutes and decrease of subsequent ageing hardening effect. In the quench sensitive range, primary precipitating reasons of rod-shaped θ particles are high diffusion rate of solute atoms and large phase transformation driving force. Therefore, for large 2219 aluminum alloy forgings, the quenching cooling rate should be increased as high as possible in the quenching sensitive range (300–480 °C) to obtain high mechanical properties, and decreased properly from the solution temperature to 480°Cin order to reduce the residual stress.