Research On The Liquid Forging-Isothermal Forging Of ZK61-Y Magnesium Alloy Wheel Hub With Its Microstructure And Properties

Magnesium is one of the ten most widely distributed elements in nature.The density of magnesium alloy is about 1.738g/cm~3,which is only 2/3 of aluminum alloy and 1/4 of steel.The specific strength and specific stiffness are roughly similar to aluminum alloy and steel.Based on the application background of a special wheel hub,this project designed a liquid forging die.Studied the influence on microstructure and mechanical properties at ambient temperature of liquid forging parts with different contents of Y element.And the evolution of the second phase in the matrix after adding different contents of Y element.The results show that when 1%Y element is added,the mechanical properties of the liquid forgings are the best at ambient temperature,the elongation rate is 16.0%,the yield strength is 104MPa and the tensile strength is 232MPa.With the increase of the content of element Y,the formation order of the second phase is I phase?W phase?Z phase.Meanwhile,I phase and Z phase formed after liquid forging have the effect of grain refinement,while W phase was no.The isothermal forging process was simulated by Deform-3d software.The effects of deformation temperature and deformation velocity on the temperature field and stress field of the parts are studied.The results indicate that with the increase of forging temperature,the force required for deformation of the blank decreases,and the temperature inside the blank increases obviously.As the deformation velocity increases,the force required for the deformation of t he blank increases,and the temperature inside the blank increases obviously.Isothermal forging experiments at different temperatures were carried out to study the effects of deformation temperature on microstructure,mechanical properties at ambient temperature and second phase,and explore the strengthening mechanism of isothermal forging on liquid forgings.The results show that when the deformation temperature is 380?,the performance is the best,the elongation is 18.5%,the yield strength is 150MPa,and the tensile strength is 315MPa.Dynamic recrystallization,second-phase hardening and work hardening are the reasons for improving the performance of the parts after isothermal forging.The most suitable process parameters are decided:deformation temperature 380?,deformation speed 10mm/s.After solid solution treatment,the structure of the alloy was recrystallized,and the grain size is 7?m~8?m.The overall trend of mechanical properties at room temperature is obtained:strength decreases and plasticity improves.Solid solution treatment at 520?for 1h showed the best performance,with tensile strength of282MPa,yield strength of 125MPa and elongation of 25.5%.The transformation process of the second phase is as follows:I phase?W phase?Mg2Y+MgZn2.The second phase can be clearly observed on the fracture surface.With the increase of solid solution time and temperature,the second phase gradually becomes granular and spherified from the long strip distributed along grain boundary.At the same time,the second phase observed at grain boundary gradually decreases,indicating that the second phase gradually dissolves into the crystal.