Hot Deformation Behavior of 6451 Alloy Sheet for Automotive Cover
The hot compression test was conducted on 6451 aluminum alloy by Gleeble-3500 thermal simulation test machine to investigate relationship between hot compression flow stress and strain of alloy under the deformation tem-peratures of 350～560 ℃ and strain rate of 0.01～20 s−1. The processing map was established and optimal hot process window was determined. Furthermore,hot deformation mechanism was explored by scanning electron microscopy (SEM) equipped with electron backscatter diffraction( EBSD). The results indicate that the flow stress of 6451 alloy exhibits positive strain rate sensitivity and negative temperature sensitivity. Under lower temperature and strain rate,strain is concentrated at the center,and great difference between the center and surface leads to the flow instability. Under the condition of 1～20 s−1 and 350～480 ℃ or 0.1～10 s−1 and 480～560 ℃,6451 alloy exhibits excellent hot processing performance. With lower deformation temperature and higher strain rate,the soft mechanism of 6451 alloy is characterized by dynamic recovery. With the increase of temperature and decrease of strain rate,the fraction of small angle grain boundary is decreased and that of large angle grain boundary is increased. Meanwhile,subcrystalline size is increased,and recrystallized grains can be observed,where the soft mechanism is converted from dynamic recovery to the co-exist of dynamic recovery and recrystallization.
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