Abstract: During the electronics assembly process,the direct low-temperature soldering between Al substrate and electronic devices is difficult because of the poor solderability of Al alloy.In this study,active soldering of 5A06-Al alloy was performed at 260℃by using Sn1Ti0.3Ga alloy solder and Ni-10wt%Cu alloy skeleton reinforced Sn1Ti0.3Ga composite solder,respectively.The effects of solder compositions and soldering time on the microstructure and mechanical properties of the joints were investigated.The results show that the alloy solder and composite solder can realize the fluxless joining of Al alloy.When soldered with the alloy solder,the layered inclusions are formed in the solder seam due to the stripping of oxide film from the Al surface,and intergranular diffusion occurs in the Al substrate.When soldered with the composite solder,the Al₃ (Ni,Cu)₂ flocculent dispersive phase is generated in the solder seam,and the (Cu,Ni)₆Sn₅ phase is formed on the alloy skeleton surface;moreover,the Al₃(Ni,Cu)₂ flocculent phase is gradually replaced by the(Cu,Ni)₆Sn₅ phase with the soldering time increasing.The shearing test results show that the joints using composite solder has higher shear strength than that using alloy solder,and the highest strength value of 31.42 MPa is obtained when soldered for 30 min.