Abstract: Tungsten inert gas (TIG) welding tests were conducted on AlMg4.3Mn0.6Cr0.12-H321 alloy with varied micro-alloying elements using ER5B71 filler wire. The influence of micro-alloying elements Zr, Er, and Sc on the microstructure, microhardness, and mechanical properties of welded joints was systematically investigated. The results indicate that the base material exhibits a deformed band structure, while the weld zone exhibits an equiaxed solidification microstructure. The addition of micro-alloying elements Zr, Er, and Sc forms nanoscale precipitates in the matrix, which effectively pin dislocations and inhibit alloy recrystallization. Compared with adding Zr element alone, adding Zr, Er, or Zr, Sc elements can more effectively suppress recrystallization behavior in the weld heat-affected zone (HAZ) and reduce base material softening during welding. All five groups of joints show W-shaped symmetrical microhardness distributions along the weld centerline, reaching minimum values in the HAZ. Correspondingly, tensile samples all fractured in the HAZ. The butt joint strength gradually increases with the variety and content of micro-alloying elements. When the Er content is 0.35%, the samples achieve the tensile strength of 274 MPa with a joint efficiency of 83.3%. The Zr-Sc co-doped samples (#5) achieve the maximum tensile strength of 293 MPa, corresponding to a joint efficiency of 89.7%.