The paper presents a metallographic study of aluminum alloy welds produced by friction stir welding. The weld structure is described for two alloys: Al-Cu and Al-Mg. It is shown that friction stir welding provides a fine-grained structure of the weld. The phase composition of the weld metal for the studied alloys is defined. Differences in the structure and distribution of secondphase particles in the weld metal are shown. The weld zone of Al-Cu alloy consists of equal size grains, with intermetallic particles located along the grain boundaries. The weld structure of Al-Mg alloy is banded, with alternating layers consisting of different size grains.