 The study investigates the impact of erbium, a, on crack reduction in selective laser-melted 7075 aluminum alloy using SEM, XRD, and HRTEM to characterise a evolution. Results show that while it reduces crack density, it increases porosity due to unmelted particles and Ul3R formation, which deteriorates fluidity and favours grain refinement for crack reduction. This article was authored by Suhui Zhong, Chen Xiao, Wenhui Yu, and others.