In this study a welding window was constructed for the relatively new welding process of friction-stir welding (FSW) to join the 6-mm-thick dissimilar aluminium alloys AA5083-H111 and AA6351-T6. The dissimilar joints were fabricated using different combinations of tool rotational speeds and welding speeds. The effect of the process parameters on the macrostructure of the joints was analysed and reported. Established along with the macrostructural analysis, a welding window was made. These windows will act as reference maps for selecting the appropriate FSW process parameters to produce defect-free welds of dissimilar aluminium alloys. Keywords: friction stir welding, dissimilar joints, welding window, macrostructure V {tudiji je bilo postavljeno varilno okno, za relativno nov postopek torno vrtilnega varjenja (FSW), za spajanje razli~nih aluminijevih zlitin AA5083-H111 in AA6351-T6 debeline 6 mm. Zvari so bili izdelani s pomo~jo razli~ne kombinacije rotacijskih hitrosti orodja in hitrosti varjenja. Analiziran je bil vpliv procesnega parametra na mikrostrukturo zvarov. Na podlagi analize makro strukture je bilo postavljeno okno za varjenje. Ta okna slu`ijo kot referen~na pri izbiri ustreznih parametrov torno rotacijskega varjenja razli~nih aluminijevih zlitin, za izdelavo zvarov brez napak. Klju~ne besede: torno vrtilno varjenje, spoji razli~nih materialov, varilno okno, makrostruktura