Processing and characterization of AZ91 magnesium alloys via a novel severe plastic deformation method: Hydrostatic cyclic extrusion compression (HCEC)

Capability of a novel severe plastic deformation (SPD) method of hydrostatic cyclic extrusion compression (HCEC) for processing of hcp metallic rods with high length to diameter ratios was investigated. The process was conducted in two consecutive cycles on the AZ91 magnesium alloy, and microstructural evolution, mechanical properties and corrosion behavior were investigated. The results showed that the HCEC process was successively capable of producing ultrafine-grained long magnesium rods. Its ability in improving strength and ductility simultaneously was also shown. The ultimate tensile strength and elongation to failure of the sample after the second cycle of the process were improved to be 2.46 and 3.8 times those of the as-cast specimen, respectively. Distribution of the microhardness after the second cycle was uniform and its average value was increased by 116%. The potentials derived from the polarization curves were high and the currents were much low for the processed samples. Also, the diameter of the capacitive arcs derived from the Nyquist curves was large in the HCEC processed samples. The finite element analysis indicated the independency of HCEC load from the length in comparison to the conventional CEC. HCEC is a unique SPD method, which can produce long ultrafine-grained rods with a combination of superior mechanical and corrosion properties.