Abstract: The phase composition, fracture morphology and mechanical properties of AZ31 alloy with different processing techniques were analyzed after aging treatment. In the coating extrusion test, 2A12 alloy was used as the cladding layer and AZ31 alloy as core material. 2A12 alloy coated AZ31 alloy composite bar with diameter of φ38 mm was prepared by reverse cladding isothermal extrusion process. The thickness of the 2A12 cladding was 4 mm and the thickness of core AZ31 alloy was 30 mm. The phase composition, fracture morphology and mechanical properties of as-cast AZ31 alloy, uncoated extruded AZ31 alloy and coated extruded AZ31 alloy were studied by XRD, SEM and tensile tests. The results show that the cladding extrusion process can improve the mechanical properties of AZ31 alloy by refining the grains and generating Al₁₂Mg₁₇ phase. In addition, for AZ31 alloys in different processing states, the extruded AZ31 alloy achieves a remarkable improvement in mechanical properties after solid solution treatment at 420 ℃ for 6 h followed by water quenching and aging treatment at 330 ℃ for 12 h. It is proved that the aging treatment has a significant effect on the mechanical properties of AZ31 alloy coated extruded bars