Phase evolution of a heat-treatable aluminum alloy during laser additive manufacturing

Highly-dense Al-5Si-1Cu-Mg alloy bulk was firstly produced by laser additive manufacture (LAM) technique. LAM involves extraordinary thermal cycles and will therefore significantly affect the microstructure. In this research, the phase evolution of LAMed Al-5Si-1Cu-Mg alloy was studied in detail by characterization along the deposition direction. The rapid solidification of LAM encourages the generation of various unstable phases of vermicular Si, fishbone shaped θ-Al₂Cu, blocky π-Al₈Mg₃FeSi₆ and irregular Q-Al₅Mg₈Cu₂Si₆. As the increasing times of thermal cycling, phase evolution takes place by spheroidization of Si phases, transformation of π-Fe to plate-like β-Al₅FeSi with dissolution of θ and Q phases. In particular, after certain times of thermal excursions, many micron-sized and nano-sized Q′ phases precipitate out from matrix, and the stabilized microstructure consists of α-Al, Q′, Si and β.