Research On Upsetting Process Of AZ80 Magnesium Alloy With Large Ratio Of Height To Diameter

Magnesium alloys have excellent properties such as low density,high specific strength and specific rigidity,good damping performance,and good electromagnetic shielding effects.They are widely used in the lightweight of aviation,aerospace,automobiles,high-speed rail and other parts.High demands.Through basic research on the forming process of components with large aspect ratios,it is expected to solve the forming and integrated manufacturing problems of high-performance magnesium alloy complex components and provide new options for high-performance magnesium alloy forming.At this stage,the upsetting of magnesium alloys with large aspect ratio is still a problem to be solved urgently.In forging production,the ratio of the height to the diameter of the upsetting cylindrical bar is generally in the range of 2.5 to 3;when the height-to-diameter ratio of the bar is ?3,the upsetting deformation is prone to longitudinal bending and the deformation becomes unstable.This not only brings difficulties to the operation,but also causes the offset of the blank axis.Therefore,the key problem that needs to be solved in the blanking process is to ensure that the super-large height-to-diameter ratio bar does not produce instability and folding during the upsetting process,which is also a prerequisite for the final forming process of the entire forging.In this paper,the upsetting process with high aspect ratio is studied,using AZ80 magnesium alloy as the research object,through the numerical simulation technology of Deform software,the various basic extrusion parameters of the extruded part are simulated,according to the load,metal filling situation,Metal flow conditions,determine the influence of process parameters on deformation,and explore the feasibility of upsetting process with large height-to-diameter ratio.At the same time,it is combined with experimental trial production to complete the process and mold formulation.The microstructure of the trial samples was analyzed,and the effect of upsetting with large height-to-diameter ratio on the uniformity of the alloy structure was studied.The main conclusions are as follows:By designing the mold entry angle ?,the mold entry edge rounding R,and the bottom height angle ?,the metal flow is optimized to divert the extreme axial compressive stress generated during the upsetting and deformation to both sides,so that the blank is evenly oriented The flow on both sides and below avoids folding and bending to the greatest extent,eliminates the difficult-to-deform area of free forging and upsetting,so that the upsetting bar with large height-to-diameter ratio can obtain more uniform deformation.Through a large number of simulation results,the best process parameters are obtained:when the AZ80 magnesium alloy bar with a diameter of 50 mm is subjected to the upsetting experiment with a large height to diameter ratio,the best value of the mold fillet radius R is10 mm,and the mold entry angle ? The best value is 5°,and the best value of the height angle? of the bottom surface of the die is 8°.Through the simulation optimization and selection of various schemes,the process parameters in the experimental trial production were determined,the temperature was 380?,the extrusion speed was 5mm/s,and the graphite and Mo S2 mixed solvent were used for lubrication.The final extrusion shape and size were basically consistent with the simulation optimization results.Obvious defects and folding phenomenon.Bars with large height-to-diameter ratios are upset and formed at one time,and the uniformity is better than that of free forging upsetting.The larger the material aspect ratio,the more obvious the grain refinement.The inner region and the lower region have smaller crystal grains,showing a strong streamlined distribution,and the deformation zone is obvious.The dynamic recrystallization area is significantly increased,the average grain size is reduced to less than 10 ?m,and a relatively uniform microstructure is obtained.The material does not produce new phases under large aspect ratio deformation,but the eutectic phase breaks more obviously,the number of precipitated phases increases significantly,and the distribution is more uniform,which further promotes dynamic recrystallization.Due to the grain refinement and grain boundary strengthening of the large aspect ratio upsetting alloy,the hardness is significantly higher than that of the free forging alloy,the hardness difference in different areas is small,the overall mechanical properties are more uniform,and the large aspect ratio upsetting can obtain a large amount of deformation The ideal uniform organization.