This　study　investigates　the　effects　of　the　external　magnetic　field　on　the　microstructure　and　mechanical　property　aluminum　alloy　6061-T6　and　7075-T651　resistance　spot　welding　joints.　The　melting　behavior　of　6061　and　7075　was　analyzed　via　the　calculation　of　the　phase　diagram　(CALPHAD)　technique.　The　CALPHAD　results　indicate　that,　for　the　6061　aluminum　alloy,　the　liquid　fraction　shows　a　minimal　increase　at　the　beginning　stage　during　the　solid-liquid　phase　transition　process　but　with　a　sharp　rise　at　the　ending　stage　(near　the　liquidus).　In　contrast,　for　the　7075　aluminum　alloy,　the　liquid　fraction　gradually　increases　throughout　the　entire　solid-liquid　phase　transition　process.　The　differences　in　melting　behavior　between　the　6061　and　7075　alloys　lead　to　different　liquation　crack　morphologies　in　their　spot-welded　joints.　In　the　6061　alloy,　the　cracks　tend　to　be　＂eyebrow-shaped＂,　allowing　the　liquid　metal　in　the　nugget　to　feed　the　gaps,　and　this　does　not　significantly　compromise　the　mechanical　properties　of　the　joint.　In　contrast,　the　7075　alloy　develops　slender　cracks　that　extend　through　the　partially　melted　zone　(PMZ),　making　it　difficult　for　the　liquid　metal　to　feed　these　gaps,　thereby　significantly　deteriorating　the　joint＇s　mechanical　strength.　Compared　to　conventional　resistance　spot-welding　joints,　the　heat　exchange　between　the　nugget　and　the　workpiece　is　enhanced　under　the　external　magnetic　field,　leading　to　a　wider　PMZ.　This　exacerbates　the　detrimental　effects　of　liquation　cracks　on　the　mechanical　properties　of　the　7075　joints.　Lap-shear　tests　indicate　that　the　mechanical　properties　of　the　6061　aluminum　alloy　joints　are　improved　under　electromagnetic　stirring.　For　7075　aluminum　alloy　joints,　the　mechanical　properties　improve　when　the　welding　current　is　below　34　kA.　However,　when　the　welding　current　exceeds　34　kA,　because　the　widening　of　the　PMZ　increases　the　tendency　for　liquation　cracks,　the　joint＇s　mechanical　property　is　deteriorated.