The dissimilar joining of QAl9-4 aluminum-bronze alloy to Q345B low carbon low alloy steel was performed by fusion welding using different techniques. The results indicated a certain amount of transverse cracks and voids in the QAl9-4/Q345B joints welded by the SMAW process, while defect-free joints were obtained using the GTAW process. The microstructure of samples produced by the SMAW process exhibited transverse cracks with typical partially oxidized intergranular cracking characteristics. Banded films rich in Cu at the grain boundaries were observed, which were demonstrated to be related to premature failure of the samples under tensile and impact load, indicating that the transverse cracks are hot cracks caused by the penetration of Cu element. Good strength and good toughness of QAl9-4/Q345B welded joints were obtained by the GTAW process.