Precipitate evolution and its effect on corrosion properties of different weld joints for Al-Mg-Er alloy

The study investigated precipitate evolution and its effect on corrosion properties in Al-Mg-Er alloy welded joints fabricated by metal inert gas (MIG) and laser welding (LW) techniques. It was observed that the morphology and size of precipitates in different joints varied significantly, with 40 pm elongated precipitates occurring in the heat-affected zone (HAZ) of the MIG joint, contrasted with abundant 2 pm precipitates in the weld metal (WM) of the laser joint. Large pits were observed in the MIG-HAZ, exhibiting dimensions of 17.4 pm in length and up to 7.1 pm in depth. Contrastingly, the LW-WM revealed smaller and shallower pits around 2.2 pm in length and 0.3 pm in depth. Polarization curves revealed that the corrosion potential of MIG-HAZ was the most negative, indicating its inferior corrosion resistance, which aligned with the corrosion morphology findings. Coarsened Al6(Mn,Fe) precipitates in the MIG-HAZ notably reduced corrosion resistance, as they hindered the formation of a stable passive film. Conversely, the LW-WM featured the Al2Er0.307Mg0.693 phase around Al6(Mn,Fe), which enhanced corrosion resistance compared to the base metal due to the fine and dispersed distribution of precipitates.