Aiming at the problem of short performance of automotive Al-Mg-Si alloy laser cold metal transition (CMT) composite weld, the weld grain size was refined to improve the mechanical properties of the weld from the perspective of Ti alloying. After Ti micro-allying, the Ti(Al_1-xSi_x)₃ precipitates gradually appeared and acted as heterogeneous nucleation particles, which enhanced the nucleation rate. Moreover, the volume fraction of Ti(Al_1-xSi_x)₃ increased (1.7%?4.2%) with the addition of thicker Ti foils (40 μm?80 μm), which significantly improved the α-Al nucleation rate and effectively refined the weld grain. Consequently, the addition of 80 μm Ti foils resulted in an average gran size of only 21 μm. The grain refinement via Ti micro-allying substantially improved the microhardness and tensile strength. Following the addition of 80 μm Ti foils, the microhardness and tensile strength reached 61 HV and 225 MPa, respectively, which were 7.0% and 8.2% higher than the values obtained without the addition of Ti foils, respectively.