Atom probe tomography (APT) provides three-dimensional compositional mapping of materials at near-atomic resolution, yet the information content of APT datasets is strongly influenced by specimen preparation. Notably, Gallium (Ga) implantation during focused ion beam (FIB) milling is generally considered a limitation that complicates data analyses, particularly in aluminium. In this work, we show that Ga implantation can instead be exploited as a sensitive marker to access additional microstructural and crystallographic information directly from APT data. Using aluminium-based systems as model materials, we demonstrate that Ga segregation is highly dependent on interface structure and crystalline defect character. In additively manufactured Al-7075, Ga selectively segregates at incoherent η precipitate interfaces while remaining absent at coherent η′ interfaces, enabling precipitates coherency and nature to be inferred solely from APT measurements. In sputtered multilayer thin films composed of alternating Al and high-entropy alloy (HEA) layers, we use Ga segregation to highlight grain boundaries and reveal that Cu segregation does not occur on all grain boundaries in the Al layers. Indeed, low-angle grain boundaries, as characterized by Ga segregation on dislocations lines, remain Cu-free and would not have been evidenced without Ga contamination. These results demonstrate that Ga implantation, traditionally regarded as a limitation of FIB-prepared APT specimens, can be repurposed as an intrinsic contrast agent. More broadly, this approach extends the information accessible from APT by providing indirect sensitivity to crystallographic information without relying on complementary crystallographic techniques.