Effect Of Mg-Zn Alloys By Combined Microalloying Of Ca-Sr:Microstructure Properties And Extrusion

As an important commercial high-strength deformed magnesium alloy,extremely,the series of Mg-Zn alloy has a widly application in 3C,automotive,aerospace and other fields.The mechanical properties of existing Mg-Zn alloys are still difficult to meet the requirements of high-strength magnesium alloys,therefore,it is necessary to study the mechanical properties of Mg-Zn alloys further.Microalloying as a low-cost,high-yield method has been used in the development of magnesium alloys.Meanwhile,compared with the expensive rare earth elements,Ca and Sr have some advantages of fine structure and improved precipitation phase structure during the alloying process of magnesium alloys because of their low price,which makes the Mg-Zn series alloys have high strength and good properties of plasticity.The development of low-cost,high-strength alkaline earth magnesium alloys has become a current research hotspot in the field of magnesium alloys.This project is based on Mg-Zn alloys,in order to study the alloying mechanism of complex addition of Ca and Sr,smelting to prepare a new type of flame retardant and heat resistant high-strength magnesium alloys by adding the elements of Ca and Sr.By ways of observe microscope（OM）and scanning electron microscope（SEM）,the evolution characteristics of microstructure,precipitation phase distribution of cast,heat-treated magnesium alloy materials and the mechanical properties of deformed magnesium alloys were determined.According to the characteristics of difficult plastic deformation of magnesium alloy,the extrusion forming law was studied.Meanwhile,the correlation between chemical composition,preparation process,microstructure and performance of magnesium alloy is clearly.The main results are as follows.（1）When adding Ca in alloy,the alloy consists of magnesium matrix,MgZn and MgZn₂ phases.When Ca and Sr elements are added in combination,the high-melting Mg₁₇Sr₂ phase is formed.The strengthening mechanism of the mechanical properties by Ca and Sr elements is the pinning effect of the MgZn,MgZn₂ and Mg₁₇Sr₂ phases distributed along the grain boundary in the alloy.（2）When the content of Ca and Sr are 1.0% and 0.5% in casting alloy,respectively,the tensile strength is 141.93 MPa,yield strength is 80.11 MPa and elongation is 15.6%.When the content of Ca and Sr elements is 1.0% and 0.5% in heating treatment alloy,the tensile strength is 174.64 MPa,yield strength is 108.51 MPa,elongation is 16.2% and the micro Vickers hardness is 51.6 HV.The optimized heat treatment process system is solution and aging treatment,the solution parameter is: 350 ℃ × 12 h and the aging parameter is: 200 ℃ ×12h.With the addition of Ca and Sr,the fracture morphology of the alloy becomes brittle fracture and the main of mechanism is cleavage fracture.（3）When the content of Ca and Sr are 0.5% and 0.5% in extrusion alloy,respectively,the grain refining effect is best.Meanwhile,the tensile strength is 319.71 MPa,yield strength is 170.28 MPa and elongation is 16.2%.With the increasing of temperature at 200℃,250℃ and300℃,the high-temperature mechanical properties of the alloy decrease,gradually.When the temperature is 200℃ and the content of Ca and Sr is 0.5% and 0.5%,respectively,the tensile strength is 246.97 MPa.