.6 Xxx Is Aluminum Alloy Low-temperature Fast Extrusion Simulation Study

In the dissertation, the deformation behaviors of aluminium alloys for 6061 and 6063 during high speed extrusion process at a lower temperature have been extensively investigated with physical and numerical simulation techniques. The results are as follows: 1 . At the strain rate of less than 20s-1, the flow stress decreases with the increase of temperature, while increases with the increase of strain rate. The temperature rise increases with the increase of strain rate. The flow stress may drop after its peak value has been obtained which can be caused by heat generation that raises the temperature by about 32癈 in less than 0.05s during plastic deformation.2. At the strain rate of 20s"1 and the temperature of 450癈, the true stress-strain curves exhibit oscillations apparently and the formation of new grains during hot deformation has been found out. Dynamic recrystallization can have taken place, though there is the high stacking fault energy for aluminum alloys.3. The Zener-Hollomon parameter, Z , is defined by the expression: Z = e-exp(l71.68/RT)s-1. The constitutive equation of high temperature compression deformation for 6063 aluminium alloy is given as:Mpa4. Most of the temperature rise occurs at the initial stage of extrusion and then the temperature tends to be stable as the ram travels further. At a reduction ratio of 25:1 and a ram speed 15mm/s, for example, the temperature rise in the billet can be as much as 92.5 癈 and the maximum temperature is 522.5 癈 , which approaches the wind quenching temperature for 6063 aluminium alloy. The difference in temperature on the cross-sections of the extrudates is approximately 1 0 癈 . The results obtained are of use in providing us with the guidelines in selecting the process parameters to avoid extrusion defects and minimized the temperature variations along the extrude and on its cross section. After the pressure drops, the sudden drop of the pressure after the peak can result from dynamic recovery, dynamic recrystallization and the temperature rise.