TTT diagrams and quenching precipitation behavior of 7A36 aluminum alloy extruded plate

time-temperature-transformation (TTT) diagrams of 7A36 aluminum alloy extruded plate were determined by an interrupted-quench method. The quenching precipitation behavior was investigated by calculate phase diagram(CALPHAD) combined with optical microscopy(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM),scanning transmission electron microscopy (STEM) and high-resolution transmission electron microscopy(HRTEM). The results show that the critical quenching rate for inhibiting the phase transition of 7A36 aluminum alloy by 0. 5% is about 15. 7 degrees C/s. Based on 10% TTT diagram, the nose temperature is determined to be about 338 degrees C with the transformation time of about 22 s. The precipitation of eta(MgZn2),T(Al2Zn3Mg3),S(Al2CuMg) or Cu-Zn rich Y phases can be found depending on different isothermal holding temperatures and time, and the precipitation behavior is described in the TTT curve, which is described as a time-temperature- precipitation diagram. eta equilibrium phase tends to occur at grain boundary(GB) first and then at sub-grain boundary(SGB) and on dispersoids in the interior of grains, at higher isothermal holding temperature, the size of eta phase is larger. The electrical conductivity increases first and then decreases with the increase of holding temperature; isothermal holding at 420 r ,the increase of electrical conductivity is caused by precipitation of eta phase and T phase, while at 330 r and 240 r ,the increase of electrical conductivity is due to the precipitation of eta phase, T phase, S phase and Y phase.