Abstract: The sound LD2 Al alloy/0Cr18Ni9 stainless steel dissimilar metal joint was achieved by inertia friction welding. The joint strength after post-welding processing could reach 96% of that of the aluminum alloy base metal. The process study was conducted on the sound Al/steel joint. The interface microstructure, tightness, pressure-bearing capacity, and the hardness of the joints before and after the high/low-temperature were comparatively analyzed. The results show that the optimized welding process can obtain defect-free Al/steel dissimilar metal joints. The distribution of the interface intermetallic compounds (IMCs) layer was uniform and continuous, with the thickness of about 500 ~ 600 nm. The element diffusion was observed at the joint interface, with the generation of Si rich FeAl_x phase. The joint fracture type was the mixed fracture dominated by ductile fracture. The joints showed sound tightness and pressure-bearing capacity. After the high/low temperature cycling tests, the interface microstructure, tightness, and pressure-bearing capacity of the joints were barely changed. Compared with the initial joints and the joints after the low temperature cycling test, the hardness of LD2 Al alloy increased by about 10% due to aging strengthening.