Fig. 9 TEM images (a, b) and HRTEM image (c, d) of matrix precipitates in the AS-HAZ sample.
In WNZ, sub-grains turned to be recrystallized structure due to high weld heat input, and some Al3(Sc,Zr) particles grew slightly (Fig. 10a). It is noted that the Ashby-Brown contrasts of the grown Al3(Sc,Zr) particles become irregular, indicating that the coherency would be break down during welding. It can be observed that new 𝜂 equilibrium phase tended to attach to the grown incoherent Al3(Sc,Zr) particles and overgrew. In addition, a considerably amount of nanoscale rod-shaped 𝜂′ phase and GPII zones also be observed at higher magnification (Fig. 10b).