Aluminum alloys have been widely used in civil fields and war industry as structural materials due to their good corrosion resistance, electrical conductivity, thermal conductivity and high specific strength. But there is a serious problem of welding joints softening in welding process, which limits greatly the application of aluminum alloys. It is found that improving the composition of aluminum alloy welding wire can refine grains and enhance the mechanical properties of welding joints. Of all micro-alloying additions to aluminum, Sc offers the greatest potential for developing new light weight structural materials with excellent mechanical properties, good welding performance, desirable corrosion and creep resistance, due to the formation of extremely fine, coherent Al₃Sc particles, which can effectively refine grains and inhibit recrystallization. This aspect permits to increase the possible use of commercial aluminum alloys. The strengthening mechanism is due to the coherent thermodynamically stable particles with ordered L1₂ structure. Addition of sufficient amount of magnesium can enhance the nucleation rate of Al₃Sc. It was shown that clusters of Mg atoms were found at the center of Al₃Sc particles, suggesting that Mg promotes nucleation of these particles. Moreover, addition of zirconium substitutes for scandium(for up to half of the scandium atoms) to form Al₃(Sc, Zr) precipitates, which are more resistant to coarsening than binary Al₃Sc precipitates. Micro--alloying aluminum alloy welding wires which can be strengthened by heat treatment were designed by adding Mg, Sc and Zr to the traditional 4043 aluminum alloy welding wire, and the heat treatment process was optimized. Welding experiment was carried out using the traditional 4043 aluminum alloy welding wire and  micro-alloying aluminum alloy welding wires. After comparing the microstructures and mechanical properties of welding joints, it was found that the mechanical properties of welding joints could be improved when adding 0.25% Mg to the 4043 aluminum alloy welding wire. The yield strength increased by 12% and the tensile strength increased by 10%, while the elongation remained constant substantially. After 530℃, 2 h+170℃, 6 h heat treatment, the yield strength of the welding joints increased by 105% and the tensile strength increased by 54%. The additions of Sc and Zr to the welding wires resulted in the finer grains significantly, raising the number of strengthening phase and increasing the strength of the welding joints.