This　work　leverages　the　rapid　solidification　characteristics　of　Selective　Laser　Melting　(SLM)　technology　to　mitigate　cracking.　By　alloying　minor　amounts　of　Mg　as　a　grain　boundary-strengthening　element　into　GH4099　superalloy　and　employing　an　improved　heat　treatment　process,　mechanisms　for　improving　the　high-temperature　ductility　of　the　GH4099　superalloy　were　investigated.　The　results　demonstrate　that　Mg　enriches　at　the　interfaces　between　grain　boundary　carbides　and　the　matrix,　restricting　elemental　diffusion　between　carbides　and　the　matrix,　and　influencing　the　morphology　and　distribution　of　carbides.　Moreover,　when　Mg　added　GH4099　superalloy　in　combination　with　the　improved　heat　treatment　process　proposed　in　this　work,　the　high-temperature　ductility　efficiently　increased　from　4.3　%　to　more　than　13.5　%.　At　this　stage,　MgO　functions　as　a　nucleating　site　for　nanoscale　intragranular　carbides,　leading　to　a　considerable　increase　in　the　fraction　of　Σ3　twin　boundaries　(12.9　→　88.6　%),　while　effectively　improving　ductility　at　high　temperatures.　©　2025