Manufacture of Gradient Microstructures of Magnesium Alloys Using Two‐Stage Extrusion Dies

Abstract

This paper aims to manufacture magnesium alloy metals with gradient microstructures using hot extrusion process. The extrusion die was designed to have a straight channel part combined with a conical part. Materials pushed through this specially designed die generate a non‐uniform velocity distribution at cross‐sections inside the die and result in different strain and strain rate distributions. Accordingly, a gradient microstructure product can be obtained. Using the finite element analysis, the forming temperature, effective strain, and effective strain rate distributions at the die exit were firstly discussed for various inclination angles in the conical die. Hot extrusion experiments with a two‐stage die were also conducted to obtain magnesium alloy products with gradient microstructures. The effects of the inclination angle on the grain size distribution and hardness distribution at cross‐sections of the products were discussed. Using a die of an inclination angle of 15°, gradient microstructures of grain sizes decreasing gradually from 17 μm at the center to 4 μm at the edge of the product were achieved.