This study examines the influence of technological parameters (welding speed and heat input) in pulsed-arc MIG welding on the microstructure, microhardness, and mechanical properties of butt joints of the aluminum alloy Al–Mg–Mn 1561. A series of experiments was conducted at various welding speeds (380, 500, and 600 mm/min) with corresponding heat input values. Metallographic analysis, tensile testing, and microhardness measurements were conducted. It was found that increasing the welding speed and decreasing the heat input not only resulted in grain refinement in the weld zone and fusion lines, but also reduced the size of porosity. The microhardness of the weld increased to 780 MPa, and the tensile strength of the joint reached ≈ 360 MPa (≈ 86% of the base metal strength). The results obtained indicate that the welding mode V = 600 mm/min and E ≈ 217 J/mm is optimal for the 1561 alloy. These results can be used to optimize the welding technology of aluminum alloys in mechanical engineering and aviation.