Abstract
A new kind of compound extrusion technology including direct extrusion and shears for AZ31 magnesium billets can cause plastic large deformations and high strain rates. A series of compressive tests have been done to obtain the stress-strain curves of AZ31 magnesium alloy. Three-dimensional (3D) thermo-mechanical coupled finite element modeling of forming magnesium alloy AZ31billets into small rods at certain high ram speed and low temperature by extrusion-shears have been carried out. The simulation model has been established and meshed based on symmetrical characteristic. Computed parameters including material characteristics for workpiece and die and process conditions consisting of initial billet temperature, extrusion ratio, channel angle and ram speed have been list. The evolution of temperature during extrusion-shear process, there are hardly any temperature gradients within the workpiece, but temperature in severe plastic deformation zone increase rapidly. Strain evolutions for inner billet are larger than those of border positions. The flow velocity distribution is uniform basically which avoid the extrusion cracks to a certain degree. Experiments show that the rods with good surface smoothness can be obtained by low temperature and high speed extrusion-shear, and the alloy grains are effectively refined by dynamic recrystallization (DRX).
Highlights
Magnesium alloys is one of the lightest structural of engineering materials, but the crystal structures of magnesium alloys are hexagonal with poor cold workability, deformation mechanisms are only basal slip and twinning[1]
Somjeet Biswas et al have studied the evolution of the microstructure and crystallographic texture during torsion of a single phase magnesium alloy AM30, the results show that The observed microstructural features indicated the occurrence of continuous dynamic recovery and recrystallization[3]
There were some inherent drawbacks for microstructures of extrusion process due to uneven metal flow during extrusion-shear which causes the properties from surface to the center uneven
Summary
Magnesium alloys is one of the lightest structural of engineering materials, but the crystal structures of magnesium alloys are hexagonal with poor cold workability, deformation mechanisms are only basal slip and twinning[1]. Bulk forming operations are normally carried on at elevated temperatures for additional slip systems would move, and become available to facilitate plastic deformation. It is extensively used to produce wrought magnesium alloys[2]. Bulk nanostructure materials processed by methods of severe plastic deformation (SPD) such as equal channel angular extrusion (ECAE)[4]. Ramin Jahadi et al has researched effect of ECAE process on the microstructure and mechanical properties of wrought AM30 magnesium alloy, The grain structure was refined from original size 20.4 μm to 3.9 μm through the four passes[5]
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