Grain Growth Model of Ultra-Fine Grain AZ80 Magnesium Alloy Multi-Directionally Forged During the Isothermal Heating Process

Abstract

This paper takes the ultra-fine grain AZ80 magnesium alloy multi-directionally forged as the research object. We observe its heating behavior at 673 K with an optical microscope, analyze the grain size distribution, and the change of average grain size and hardness with different heating time, study the effect of heating time on the grain size change of ultra-fine grain AZ80 magnesium alloy, deduce and verify the grain growth model of ultra-fine grain AZ80 magnesium alloy during its heating process. The research results show that the 24-pass multi-directional forging can make ultra-fine grain AZ80 magnesium alloy of an average grain size of 0.73 μm. When ultra-fine grain AZ80 magnesium alloy is isothermally heated at 673K, its average grain size grows continuously as time extends. Its average grain size and hardness fall into two stages as the heating time changes, namely rapid grain growth stage and stable grain growth stage. If the heat preservation time is less than 300 s, the average grain size grows rapidly as temperature rises; When the heat preservation time reaches 300 s, the grain growth speed will be stable. A grain growth model is established for AZ80 magnesium alloy, which is D^2.8932 = D₀^2.8932 + 4.09086 × 10^-3t^1.6284 under the conditions of isothermal heating, whose computed result well coincides with the measured value.