To address the quality challenges in welding thin-walled special steels with weather-resistant steels of dissimilar materials

a systematic study of laser filler welding processes was conducted using 4.5 mm thick special steel and 2.5 mm thick Q345NQR2 weather-resistant steel in large structural components. The results show that the low heat input characteristics of laser filler welding can effectively reduce the width of the heat-affected zone

preventing grain coarsening on the Q345NQR2 side and hardened structure formation on the special steel side. By using H1Cr21Ni10Mn7Mo austenitic stainless steel filler wire

the differences in properties between the dissimilar steels can be mitigated

achieving an average tensile strength of 81% of the base material. Moreover

the weld formation is aesthetically pleasing

with minimal spatter

significantly reducing the cost of subsequent cleaning. Although MAG welding has lower equipment costs and greater operational flexibility

its high heat input leads to a wider heat-affected zone and increased deformation (longitudinal shrinkage is about 35% higher than that of laser filler welding)

and its joint tensile strength is only 43% of the lower limit of the special steel base material. Furthermore

the study clarified the formation mechanisms of cracks and pores in dissimilar steel welding and proposed a pore suppression strategy of "slightly faster welding speed + positive large defocus + negative appropriate oblique incidence + high power compensation for melt depth"

which can control welding deformation within 1.5 mm/m. In conclusion

laser filler welding is more suitable for scenarios requiring high welding quality and structural accuracy

while MAG welding is best suited for cost-sensitive situations with moderate quality requirements. The research provides engineering references for optimizing the welding process of thin-walled dissimilar steel large structural components.