The correlation between Si content （0.1%-0.5%, mass fraction） and pulse laser welding performance of AI-Mn-Mg aluminum alloy sheets was studied. The sheets were fabricated in the laboratory, with gauge of 0.45 mm, H16 temper by pulse laser welding. It was found that no cracking existed in the welding pool as Si content was below 0.34%. However, when the Si content increased to 0.47%, cracking formed in the welding pool. Microstructure observations indicated that residual eutectic phases distributed at the grain boundaries were discontinuous and appeared to be small particles in lower Si content alloys; the residual eutectic phases distributed at the grain boundaries were partially continuous and appeared to be films in higher Si content alloys. These phenomena could explain why Si content adversely affected the laser welding performance.
