Investigation On The Hot Deformation And Heat Treatment Of The As-Extruded AZ80Magnesium Alloy

Hot compression was conducted on an extruded AZ80magnesium alloy using Gleeble-1500thermal simulation machine. After correction of flow stress data, the apparent deformation activation energy and Zener-Hollomon parameter were calculated and the constitutive equation of extruded AZ80magnesium alloy was established. The processing map of extruded AZ80magnesium alloy was studied. The effects of temperature and strain rate on the critical strain of dynamic recrystallization and the strain rate sensitivity coefficient was discussed, and the microstructure evolution under different thermal deformation conditions was analyzed using optical microscopy and transmission electron microscope. Besides, using hardness testing machine, mechanical properties testing machine, differential thermal analyzer, X-ray diffraction, optical microscopy and scanning electron microscopy, the effect of solid solution and ageing treatment on the microstructure, hardness and mechanical properties of extruded AZ80magesium alloy were studied. The main conclusions obtained in this study are as follows:(1) The true stress-strain curves of extruded AZ80magnesium alloy indicate the occurrence of dynamic recrystallization. A lower temperature or a higher strain rate leads to a higher peak stress and a larger strain at peak stress.(2) The constitutive equation applicable to the extruded AZ80magnesium alloy in this study is: ε=5.14×109[sinh(0.008σ)]5.32exp[-132577/RT]The average deformation activation energy of extruded AZ80magnesium alloy is132.577kJ/mol. Deformation activation energy increases with the increase in temperature or the increase in strain rate.(3) At a constant strain rate, a higher temperature contributes to a smaller critical strain for dynamic recrystallization in extruded AZ80 magnesium alloy, while a higher strain rate causes a larger critical strain at the same temperature. As for the same strain, the strain rate sensitivity of extruded AZ80magnesium alloy varies greatly at low temperature while stays relatively stable at high temperature.(4) The energy dissipation efficiency of extruded AZ80magnesium alloy at high temperature varies slightly and stays around0.2-0.3, while changes hugely at low temperature. instability occurs more prequently when the alloy is deformed at temperature below350℃. After a comprehensive analysis, the most suitable hot deformation process for extrusion state AZ80magnesium alloy in this study is400℃tempearure and0.1s-1strain rate.(5) Obvious characteristics of age hardening can be observed for the T5and T6aging treatment in extruded AZ80magnesium alloy. The highest tensile strength of the T5state for extruded AZ80magnesium alloy can be acquired at temperature of175℃for30hours and reaches339MPa with the elongation of10.4%. to coMPare with, the highest tensile strength for the T6state is acquired at tempearature of175℃for25hours after2hours’solid solution at420℃and it arrives at350MPa while its elongation is8.3%.