Process And Mechanism Of Inertia Radial Friction Welding On 7A04 A1-T2 Cu Dissmilar Meatal Materials

The aluminum and copper has been increasing used in industry, however, there is a distinct difference among the chemical composition, mechanical properties and melting-point of the two materials, the welding of aluminum and copper dissimilar metals has always been a difficulty in materials science. The inertia radial friction welding is a solid state welding technique which utilizes friction heat to realize materials joining; it has overwhelming advantages in the welding of dissimilar materials. Therefore, this paper aimed at the dissimilar welding of 7A04 aluminum alloy bar and T2 copper ring and studied the feasibility of radial inertia friction welding method.However, there is little research on dissimilar friction welding of aluminum and copper presently. In this paper, by the means of experiment method, the macro-morphology, flash profile and structure of the welded joints obtained by experiments were analyzed. The microstructure of the joints was observed by optical microscope(OM) and scanning electron microscopy(SEM). The hardness and shear strength of the joints were tested. The results show that the dissimilar welding of 7A04 aluminum alloy bar and T2 copper ring by radial inertia friction welding method is feasible. Under a maximum speed of 4100r/min, a prior friction speed and a friction speed of 4000 min, a forging speed of 2000r/min, and a forging pressure and a friction pressure of 8.0MPa and 4.0MPa, respectively, the most stable joints with the best quality were obtained from the experiments. The plastic deformation layer, dynamic recrystallization and element diffusion miscibility were found in the interface, and metallurgical bonding was realized. The joint included three zones: fine grain zone(FGZ), transitional zone(TZ) and heat affected zone(HAZ). The grains in the FGZ and HAZ were circular granular; the grain size in FGZ was small, and the grains in HAZ were coarse, with a grain size larger than the grains in base metal(BM). The grains in TZ exhibited slender shaped structure, and have different sizes, but the average size of the grains was between in FGZ and BM. The test results of the micro-hardness and shear strength of the joints were in agreement with the macro-morphology and microstructure analysis.The formation mechanisms of flash were also analyzed in this paper, and the flash effect was proposed, and the influence of parameters on joints quality was analyzed. The results show that the formation mechanisms of flashes were: under the action of tangential component of radial force and frictional force, the materials were led to the materials flow in the direction of resultant force. The larger resultant force, the faster the materials flow speed, and hence the flashes were formed. Removing the oxide layer on the surface of the aluminum before welding is very important. In this paper, the oxide layer was extruded in the form of flashes. The amount of flashes can be expressed as the burning value. The optimal burning value in the Al-Cu radial inertia friction welding is between 3.0mm and 3.5mm in this paper. The forging pressure and friction pressure have a dominant influence on the burning value; the friction pressure is correlative to the burning value, the bigger the friction pressure, the higher the burning value; the smaller the friction pressure, and the lower the burning value. The friction pressure has a great influence on the quality of welded joints. When the friction pressure is greater than 4MPa, the quality of the welded joints is better, and defects not prone to form in the joints.