The　self-piercing　riveting　(SPR)　process　was　used　to　join　2.0-mm-thick　aluminum　alloy　6061-T6　and　1.2-mm-thick　mild　steel　SPFC340　sheets.　SPR　joints　produced　with　a　conventional　flat-bottom　die　and　conical-section　dies　were　investigated　both　experimentally　and　numerically.　Lap　shear　tests　were　conducted　under　quasi-static　conditions　to　evaluate　the　load-carrying　capability　of　these　SPR　joints.　The　effect　of　variation　in　die　geometry　(such　as　variation　in　the　die　groove　shape,　cone　height,　and　die　radius)　on　the　main　mechanical　response　of　the　joints,　namely　the　peak　load　and　energy　absorption,　was　discussed.　The　results　showed　that　SPR　joints　produced　with　the　conical-section　dies　exhibited　a　failure　mode　similar　to　those　produced　with　a　conventional　die.　All　the　joints　failed　by　tearing　of　the　top　steel　sheet.　Cracks　that　occurred　in　the　bottom　aluminum　alloy　6061-T6　sheet　around　the　rivet　leg　were　a　result　of　tangential　tensile　stress.　The　cone　height　of　a　conical-section　die　is　the　most　important　parameter　affecting　the　surface　quality　of　Al/steel　SPR　joints.　Conical-section　dies　with　a　moderate　convex　can　ensure　a　good　surface　quality　during　the　SPR　process.　In　addition,　SPR　joints　with　single　conical-section　die　allow　higher　tensile　strength　and　energy　absorption　compared　to　those　with　double　conical-section　die.