The formation of Al3(Sc xZr yHf1-x-y)-dispersoids in aluminium alloys

The nucleation and growth of dispersoids during precipitation annealing of Al-Hf-Sc-(Zr)-alloys have been studied by 3D atom probe and TEM. A high number density of Sc-rich clusters was observed in the early stages of precipitation, and these clusters subsequently transform to spherical Al3Sc-dispersoids displaying the L12-structure. Further annealing results in segregation of Zr, Hf and more Sc to the Al3Sc/α-Al matrix-interfaces, and upon completion of precipitation annealing Zr-, Hf-, and Sc-containing 'shells' were observed around already existing Al3Sc-dispersoids. A previously developed non-isothermal theoretical approach to diffusion has been used in order to interpret these observations