Study Of The Forming Process Of The Minor Diameter Thin Wall Magnesium Alloy Tubes

The extruding process of forming AZ61 Magnesium alloy was studied in this page,by comparison,hollow billet inverse forming process by extrusion is selected as experimental research.The forming parameters were determined,the inverse forming die was designed. During the process of experiment the die structure and forming parameters were optimized, and the forming process of the minor diameter thin wall Magnesium alloy tubes was implementated.The change of microstructure of the Magnesium alloy tubes by extrusion at the temperature of 400℃was analyzed as well,then the effect of the extrusion ratio on the tubes microstructure was studied.The mechanical property of extruding state and four different heat-treatment extruding tubes are measured,different extrusion ratio and different heat-treatment impacted the mechanical property of AZ61 Magnesium alloy is analyzed.The experiment results indicate that:hollow billet inverse forming process by extrusion is selected,that is,blanking—homogenerity heat treatment—oxide removal—preparation for hollow billet—surface treating—tube extruding,the degree of eccentricity of the Magnesium alloy tube after extrusion is reduced obviously,and the inner and outer surfaces are improved,even there is no cracks at the exit.Compared with extrusion,the damage of the extrusion needle for inverse extrusion is controlled to a small extent,due to the minor diameter,the thin wall,the thin extrusion needle,and the large positive extrusion load.At the aspect of mould design,through the abrasive machining polished finish after quenching treatment,there is no bonding phenomenon between the extrusion bobbin,the cavity die and the extrusion needle.The initial deviation of central line between the extrusion needle and the cavity die is reduced through improving the assembly accuracy between the extrusion needle and the cavity die.Reducing the extrusion force and the major diameter of the extrusion needle,and the credible allocation of the billet can contribute to the control of the wall thickness error of the tubes.The microstructure of the Magnesium alloy is refined,that is,the rough fir-tree crystal as cast condition is inverted to the thin strip crystal after hot extrusion processing,and the β-Mg₁₇Al₁₂ phase is inverted from the continuous reticular distribution to the state of streamline,to some extent,the deficiency such as rarefaction in the casting structure is removed and the density is improved accordingly.Both the rate of elongation and the strength of the alloy are improved due to the refining of the crystal via extrusion.Under the condition of different extrusion ratios,the mechanical properties of the extrusion tubes are always better than normal.The best of all is the AZ61 Magnesium alloy with the extrusion ratio selected as 23,the tensile strength of which reached 290.5MPa,the yield strength reached 202.3MPa,and the elongation reached 5.3%.After the heat treatment of T6,the maximum tensile strength can reach 362.8MPa,which is raised as 24.9%compared to the extrusion condition.The yield strength is increased to 258.2MPa, which is improved as 27.6%than that in the state of extrusion.