Identification of nucleation mechanism in laser welds of aluminum alloy

The nucleation mechanism in laser welds of aluminum alloys is still unclear. Here, we identified it for the first time by adopting an overlap welding procedure. The commonly used 5083 aluminum alloy was taken as an example. The variation of grain structure and grain size in different overlap welding cases was characterized by electron-backscattered diffraction. Results revealed that the nucleation mechanism was heterogeneous nucleation, rather than grain detachment and dendrite fragmentation. Furthermore, the chemical composition and phase structure of the heterogeneous nuclei were tested by energy-dispersive spectrometer and transmission electron microscopy, which indicated that they were D0(22) Al3Ti phase. The present study is significant in that it can provide a theoretical basis for grain refining in laser welds of aluminum alloys.