Homogenization And Isothermal Multi-Pass Hot Compression Deformation Behaviors Of 7N01 Aluminum Alloy

Owing to high strength, good extrusion, excellent weldability and resistant corrosion etc,7N01 aluminum alloys have been produced as the basic structural materials of high-speed train, body, chassis, frame etc. Its high strength and low weight effectively save energy and reduce operating and maintenance costs. In order to meet the rapid development of China's high-speed rail transit and solve hot tearing problem in thermal processing of the alloy, the homogenization treatment and isothermal multi-pass hot simulation compression process of 7N01 aluminum alloy were studied in this paper. The microstructure evolution of 7N01 aluminum alloy during the homogenization process, and the softening mechanism during the multi-pass hot compression have been analyzed. The main conclusions are as follows:1. Non-equilibrium microstructures of 7N01 aluminum alloy ingot were formed during fast cooling process. Serious segregation of Zn and Mg elements in the vicinity of the grain boundaries formed the low melting phase MgZn2, while coarse impurity phase Al16(Fe(1-y), Mny)4Si3 exists on the grain boundaries.2. The suitable single stage homogenization process for 7N01 aluminum alloy is 470?/24h. In this process, the grain boundary becomes fine, the low melting point phase has been basically eliminated, and most of the residual impurity phase were dissolved.3. The main evolution mechanism of particle (GB) along grain boundary in the homogenization process is the thinning, spheroidized and the full dissolution. Dissolution of GB particles mostly depends on the temperature.4. The hardness of 7N01 aluminum alloy under single stage homogenization at temperatures of 400?,505?and 540? are lower than that of the as-cast 7N01 aluminum, while the hardness homogenized at 435 ? and 470? are higher than that of the as-cast alloy. Homogenized at 400 ?,435? and 470 ?, the electrical conductivity of 7N01 aluminum alloy are higher than that of the as-cast alloy, but the electrical conductivity are lower than that of the as-cast alloy at 505 ? and 540?. 5. The two-stage homogenization treatment can dissolve more non-equilibrium bulky phase and effectively eliminate dendritic segregation than single-stage homogenization. Appropriate two-stage homogenization system is 420?/24 h+470?/24 h. In this case, the eutectic phase dissolved fully, and the composition is more uniform. 6. The appropriate three-stage homogenization system is 420?/10 h+470 ?/24 h+485?/30 min, in which grains are more fine and uniform. 7. At high strain rate (1.0s-1), the thermal deformation stress of isothermal multi-pass hot simulation compression is lower 15%than that of the single pass.With the increase of strain the stress increased to a maximum and maintain steady state. Under low strain rate (0.01 s-1), flow stress increases quickly to reach the peak stress and drops rapidly, then reached a steady state.8. In isothermal multi-channel hot deformation process, due to the static softening of the passes, the flow stress (strain) of 7N01 aluminum alloy apparent static softening characteristics, and the rheological stress of holding time at 10s was higher than the 100 s.9. At the high strain rate (1.0s-1), the main softening mechanism of the 7N01 alloy was found to be dynamic and static recovery. At the low strain rate (0.01s-1), the main softening mechanism of 7N01 alloy was from recovery to recrystallization.