The joining of arc-sprayed aluminum coatings to AZ91D substrates was achieved by solid-liquid bonding method, and the microstructures, elements and phases of the interface were analyzed. The results show that hole-defect is usually occurred in the interface after the coatings were cleaned by surface treatment. Metallurgical bonding is formed between the untreated aluminum coating and AZ91D substrate, and intermetallic compound layers are found in the interface. As the pouring temperatures rise, the diffusion regions become larger, and the coatings are gradually transformed into Al12Mg17 and Al3Mg2. The heat treatment on the composite can lead to a uniform structure and a larger diffusion region.