Effects Of Heat Treatment And Forward Extrusion On Microstructure And Mechanical Properties Of Mg-Zn-Sn-Ca Alloy

In recent years,the excellent biocompatibility of magnesium alloys has made it widely used in biomedical surgical implant materials.In this study,Mg-Zn-Ca,which is close to bone density,is used as a matrix,and Sn is harmless to the human body for alloying.The prepared material may become a substitute for titanium alloy and stainless steel,which will benefit humans in medical devices and other aspects.The microstructure and mechanical properties of Mg-2Zn-x Sn-0.5Ca alloy before and after modification were investigated by using different test methods such as optical microscope,scanning electron microscope,X-ray diffraction analysis,and hardness test.By changing the content of Sn elements,the effects of changes in the content of Sn elements?x=0,2,4,6?on the microstructure and mechanical properties of Mg-2Zn-4Sn-0.5Ca alloys were investigated,and the best alloying was obtained.The composition is Mg-2Zn-4Sn-0.5Ca.On this basis,the alloy was subjected to positive extrusion treatment to explore the effect of extrusion ratio and aging treatment on Mg-2Zn-4Sn-0.5Ca.The effect of Sn alloying on Mg-2Zn-x Sn-0.5Ca alloy was explored by adjusting the content of Sn element.It was found that after adding Sn?Sn<6wt.%?To Mg-2Zn-0.5Ca alloy,new high melting point Mg₂Sn phase was formed in Mg-2Zn-x Sn-0.5Ca alloy,and high melting point Mg₂Sn broadened Mg-2Zn-0.5Ca alloy deformation temperature and rate,so compared with other Mg-Zn-Ca or Mg-Al alloys,the addition of Sn reduces the alloy's hot brittleness.With the increase of Sn content,the tensile strength of the alloy tends to increase first and then decrease.When the content of Sn is 4 wt.%,the ultimate tensile strength of the Mg-2Zn-x Sn-0.5Ca alloy reaches the maximum,and the value is 163 MPa.At this time,the elongation of the alloy is 14.8%.The main reason for the above phenomenon is that when a small amount of Sn element is added to the Mg-2Zn-0.5Ca alloy,Ca Mg Sn and Mg₂Sn strengthening phases are formed in a granular form.When the Sn content is too high,Mg₂Sn aggregates and becomes the crack germination point during stretching.Through the heat treatment research of Mg-2Zn-4Sn-0.5Ca alloy,the effect of solution treatment and aging strengthening on the microstructure of as-cast alloy was analyzed.After analyzing the solution treatment,it can be found that the microstructure and mechanical properties of the Mg-2Zn-4Sn-0.5Ca alloy reach the best when the solution is treated at 475?for 10 hours,and the room temperature tensile strength and elongation of the alloy reach 177 MPa and 18%.After aging treatment of the best solid solution alloy,its mechanical properties are further improved,but its elongation is significantly reduced.According to the fracture morphology analysis of the alloy,it can be seen that many cleavage planes appear in the fracture planes of the as-cast alloy.After the solution treatment,the cleavage planes at the fracture plane of the alloy are significantly reduced,and the dimples begin to increase.The fracture mode obviously changed from as-cleaved cleavage fracture to quasi-cleavage fracture.After the aging treatment,the grain boundary of the second phase detached appeared on the fracture of the alloy,which was mainly caused by the precipitation of more hard and brittle phases after the aging treatment.The shape deformation treatment was performed on the solid solution alloy by means of positive extrusion deformation.The effect of extrusion ratio on the microstructure and mechanical properties of Mg-2Zn-4Sn-0.5Ca was investigated.After the solid solution alloy is extruded with different extrusion ratios?4,11,25?,the tensile strength of the alloy is significantly improved.When the extrusion ratio is 25,the tensile strength of the alloy can reach 309 MPa.Aging treatment was performed on the alloy after extrusion,and the age hardening curve of the alloy was analyzed.The study found that when the alloy was aged at 200?,the hardness of the alloy reached a peak after 40 h.On this basis,transmission analysis of the extruded and peak-aged alloys was carried out.Analysis shows that fine Ca Mg Sn and Mg₂Sn phases are precipitated in the crystals of the alloy after aging treatment,which leads to an increase in the hardening degree of the alloy.