Ultra-high Pressure Hydrostatic Extrusion Forming Process And Properties Of AZ80 Magnesium Alloy

In this paper,the forming process of ultrahigh pressure hydrostatic extrusion of AZ80 magnesium alloy was researched.First of all,the overall scheme of ultrahigh pressure hydrostatic extrusion system was made,the forming process of it was determined,and the theoretical study on critical process parameters and the principle of hydrostatic extrusion were conducted in depth.Meanwhile,the forming process schemes of large diameter magnesium alloy tubes and thick wall magnesium alloy tubes were established with related die designed.Then,the process of ultrahigh pressure hydrostatic extrusion was simulated by using DEFORM-3D finite element software.The distribution law of the temperature field of the extrusion container was obtained,which is instructive to study on the hydrostatic extrusion temperature.The forming process of large diameter magnesium alloy tube's hydrostatic extrusion was simulated and analyzed.The effect of extrusion ratio on the extrusion load,equivalent strain and velocity field was studied.With the increase of extrusion ratio,the peak pressure and average pressure of the extrusion load increased.The effect of extrusion ratio on the peak pressure was greater.The distribution of formed tube's equivalent strain was analyzed.The maximum value of the equivalent strain was distributed in the extrusion deformation zone,where severe plastic deformation mainly including shearing and extrusion deformation occurred.Finally,the large diameter and thick AZ80 magnesium alloy tube were fabricated in the 40 MN horizontal hydrostatic extrusion machine.Samples from these tubes,were analyzed for the microstructure and tested for the mechanical properties.The results showed that the ultimate tensile strength and the yield strength of hydrostatic extrusion products were improved greatly,but the ductility of it was at low level.After hydrostatic extrusion,the microstructure of magnesium alloy tube was analyzed.The grains were elongated along the extrusion direction,the subgrain appeared and the grain refinement was obvious.The effect of recrystallization annealing process on property of hydrostatic extrusion products was studied,which is important to improve the plastic property of products.