Effect Of Rolling Temperature And Heat Treatment On Mechanical Properties And Corrosion Resistance Of Mg-2Zn-0.5Nd-0.5Zr Sheet

As a new generation of biodegradable medical metal materials,magnesium and its alloys have been attracted much attention.Bone plate is one of the application fields of medical magnesium alloy implants.During implantation,bone plate will be subjected to tensile,compression,bending and other stresses,so it needs to have high strength,so as to achieve good fixation and support effects.However,compared with the traditional titanium alloy bone plate,the strength of magnesium alloy is lower,meanwhile,the corrosion potential of magnesium alloy is low and it corrodes easily.Therefore,in order to improve the plasticity and toughness of magnesium alloy sheet to adapt to the complex stress environment in vivo and improve the corrosion resistance of the plate to reduce the average corrosion rate of the plate during service,which is the main research direction of medical magnesium alloy sheet at present.The newly developed Mg-2Zn-0.5Nd-0.5Zr alloy has potential application in medical magnesium alloy products,but the alloy sheet has not been systematically studied Therefore,a series of rolling and some heat treatment experiments were carried out on this alloy.The effects of different rolling temperatures on the mechanical properties and corrosion resistance of this alloy were studied and the rolling parameters suitable for the alloy were obtained.At the same time,to further improve the corrosion resistance and plasticity of the sheet,a series of heat treatment plans were applied.There are many significant research results,which provided certain theoretical guidance for the development of this magnesium alloy.In this study,two kinds of heat treatment process were employed before rolling and two kinds of sheet with coarse and fine microstructure were obtained,and then rolling experiments were carried out on these two kinds of sheets.And then the rolling experiments were carried out at 230℃,280℃ and 330℃.The results show that with the increase of the rolling temperature,the strength of the two kinds of plates decrease and the plasticity and corrosion resistance increase.The rolling temperature has great influence on the mechanical properties of the initial fine grain sheet.The dynamic recrystallization of this sheet occurs at 330℃ rolling temperature,and the grain structure is mostly round grain,which have the best plasticity and corrosion resistance in the same group.The rolling temperature has a great influence on the precipitate morphology of the original coarse grain sheet.At 330℃ rolling condition,only a small amount of precipitates were found at the grain boundary,which was different from the second phase morphology of the lump-like plate at the other two temperatures.And the corrosion results show that less second phase is beneficial to the corrosion resistance of this sheet.Comparing the two kinds of plates rolled at 330℃,the result of the original fine grain plate has better mechanical properties,poor corrosion resistance can be found.The different annealing temperature of the plate with fine grains and the annealing and aging of the plate with coarse grains were studied.The results show that the uniformly distributed secondary phase in fine grains plate can restrain grain growth during the annealing process,circular or elliptical shape grain morphology is obtained after annealing,which result in the significantly improved plasticity and corrosion resistance.For this plate,350℃/1h is the best annealing parameter,under which the tensile strength,yield strength,elongation and corrosion rate of this plate are 255 MPa,210MPa,22.5% and 0.12mm/y,respectively.For coarse grains plate,the grain size after annealing is relatively large and shows polarization.This rolling plate at 330℃ have the best tensile strength,elongation,and corrosion rate after annealing,which is 235 MPa,24.3% and 0.14mm/y respectively.The strength of the alloy is improved after aging.The yield strength and tensile strength of 330℃+ aging group are 275 MPa and 255 MPa,respectively which have the highest mechanical property.Although the secondary phase precipitated by aging can play a certain strengthening role,a large amount of precipitated phase harms the plasticity and corrosion resistance of this alloy.