Objective　Laser　powder　bed　fusion　(LPBF)　additive　manufacturing　technology　has　been　widely　utilized　to　fabricate　degradable　zinc　(Zn)　implants　and　is　a　novel　approach　for　creating　complex　structures　with　controllable　shape　and　exceptional　performance.　However,　printing　Zn　is　challenging　owing　to　its　evaporative　nature　and　narrow　fabricating　window　arising　from　its　low　melting　and　boiling　points.　Therefore,　a　comprehensive　investigation　must　be　conducted　to　reveal　the　mechanisms　of　heat　and　mass　transfer　in　molten　pool　during　LPBF,　which　can　provide　theoretical　guidance　for　the　optimization　of　printing-process　parameters.　Methods　A　mesoscopic-scale　heat　transfer　and　flow　coupling　model　of　molten　pool　during　the　LPBF　of　pure　Zn　was　established　using　discrete-element　and　computational　fluid　dynamics　methods.　Single　molten-track　experiments　were　designed　to　verify　the　numerical　model.　The　mechanisms　by　which　the　process　parameters　affect　the　temperature　field,　flow　field　evolution,　and　morphology　of　the　molten　track　were　discussed.　Results　and　Discussions　Pure　Zn　is　sensitive　to　changes　in　transient　heat　input　owing　to　its　low　melting　and　boiling　points.　Increasing　the　laser　power　significantly　alters　the　molten-track　size,　peak　temperature,　and　cooling　rate.　Specifically,　when　the　laser　power　is　increased　from　30　W　to　60　W　and　90　W,　the　real-time　volume　of　the　molten　pool　increases　nonlinearly　by　510%　and　1730%,　respectively　(Fig.　9).　At　higher　scanning　rates,　more　laser　energy　is　absorbed　by　the　surface　of　Zn　powder,　the　length-width　ratio　of　the　molten　pool　changes　gradually　from　1.28　to　1.98,　and　the　length-depth　ratio　changes　from　1.61　to　3.45　(Figs.　4　and　5).　Consequently,　the　molten　pool　is　longer,　shallower,　and　more　narrow,　thus　resulting　in　larger　temperature　gradients　along　the　direction　of　the　molten-pool　depth,　with　the　maximum　cooling　rate　increasing　from　3.6×106　K·s-1　to　1.3×107　K·s-1　(Figs.　6　and　7).　Furthermore,　the　real-time　volume　fluctuated　considerably　and　erratically　during　molten-track　formation.　As　the　laser　energy　density　within　the　molten　pool　increases　further,　the　internal　flow　accelerates　and　the　evaporation　of　Zn　at　the　center　becomes　evident,　thus　changing　the　Marangoni　convection　caused　by　temperature　gradient　into　evaporative　recoil　pressure　as　the　dominant　driving　force　for　flow　within　the　molten　pool.　The　morphology　of　the　printed　molten　tracks　transformed　from　central　point-like　pits　into　continuous　slitlike　shapes　(Fig.　11).　The　findings　of　this　study　can　provide　theoretical　guidance　for　the　evolution　of　the　molten　pool　and　for　optimizing　the　LPBF　processing　of　metals　with　low　melting　and　boiling　points.　Conclusions　(1)　Significant　evaporation　is　observed　under　high　laser　power　during　the　LPBF　printing　of　pure　Zn,　whereas　the　molten　tracks　indicate　low　stability　at　high　scanning　rates.　Under　laser　power　levels　and　laser　scanning　rates　of　45‒60　W　and　300‒600　mm·s-1,　respectively,　the　simulation　results　indicate　strong　metallurgical　bonding　between　Zn　powders　and　Zn　substrate,　thus　implying　the　high　stability　of　the　molten　tracks.　(2)　The　stability　of　the　printing　process　is　affected　significantly　by　the　process　parameters　owing　to　the　low　melting　and　boiling　points　of　Zn.　Therefore,　LPBF　machines　equipped　with　the　appropriate　gas　flow　field　can　prevent　Zn　vapor　from　destroying　laser　propagation.　(3)　When　a　laser　source　with　Gaussian-distribution　characteristics　is　used,　the　temperature　in　the　central　region　of　the　molten　pool　exceeds　the　boiling　point,　even　when　a　laser　power　as　low　as　30　W　is　used,　which　is　not　conducive　to　the　stable　formation　of　Zn.　Laser-beam　shaping　or　positive　defocusing　can　be　considered　to　weaken　the　high　energy　density　in　the　central　region　of　the　laser　to　reduce　evaporation,　thus　ultimately　improving　the　forming　quality　of　LPBF-printed　Zn.　©　2024　Science　Press.　All　rights　reserved.