Research On Optimization Of Laser Welding Process Of Zr-based Amorphous Alloy Sheet

Zr-based amorphous alloys have certain applications in sports equipment,3C consumer electronics,and biomedical fields due to their low elastic modulus,excellent corrosion resistance,excellent mechanical properties,and good biocompatibility.Amorphous alloys have many advantages in properties compared with traditional crystalline alloys,but they also face problems such as small manufacturing volume,difficult processing,and poor welding performance.In this paper,Zr-based amorphous alloy due to its superior amorphous forming ability and use in the biomedical field is taken as the research object.In this paper,laser welding is selected to carry out welding experiments on Zr-based amorphous alloys.The influence of laser welding process parameters and welding heat dissipation conditions on the formation and performance of welded joint microstructure is systematically studied,and the main influencing factors of welded joint crystallization are explored.Based on the biomedical application background of Zr-based amorphous alloy,this paper evaluates the applicability of the obtained welded joints with good performance.The main research contents and achievements are as follows:1.The finite element method is used to simulate the laser welding process of reduced Zr-based amorphous alloy.Combined with Differential Scanning Calorimeter（DSC）and welding experimental results,the finite element model is optimized and improved.Finally,the actual temperature field distribution and thermal cycle curves are obtained.Combined with DSC and thermal cycle curves,the crystallization zone of the Zr-based amorphous alloy during laser welding is predicted The highest accuracy rate can reach 92%.It can better predict the position and width of the crystallization zone of the HAZ and explain the shape of the HAZ.By calculating the critical heating time of HAZ during laser welding,it is inferred that the crystallization of amorphous alloy is mainly caused by the endothermic heat absorption of HAZ.The position and size of the crystallization zone of Zr-based amorphous alloy used in this experiment can be deduced by the thermal cycle curve between DSC and HAZ,and the critical cooling time of Zr-based amorphous alloy is judged to be between 0.289 s and 0.342 s.2.According to the theory of crystallization in heat affected zone（HAZ）of amorphous alloy,the fixture is designed and improved.Under the condition of controlling other variables,the welded joints with different heat dissipation conditions and different initial temperatures were obtained by using the designed fixture to explore the Zr₆₄Cu₁₇Ni₁₃Ti₄Fe₂ Zr-based amorphous alloy.The microstructure and properties of the welded joints were observed and tested.the results show that the crystallization mainly occurs in the HAZ,and the grains in the HAZ are spherical when the cooling conditions are better.Lower initial temperature and better heat dissipation conditions can significantly reduce the crystallization of HAZ.3.The welding experiments of Zr-based amorphous alloys were carried out with different laser welding parameters,and the effects of laser welding parameters on the microstructure evolution and mechanical properties of laser welded joints were studied.The results show that the crystallization zone of HAZ of welded joint widens gradually with the increase of heat input.The microhardness of crystallization zone is about525 HV_0.2,which is slightly higher than that of base metal(470 HV_0.2)and melting zone(490 HV_0.2).The crystallization of welded joints has a great influence on the tensile strength.The tensile strength of Zr-based amorphous alloy base metal is 777 MPa,and the maximum tensile strength of welded joint is 583 MPa,which is about 75%of the tensile strength of base metal.4.Combined with the background of the application of Zr-based amorphous alloy in this experiment,corrosion resistance experiments,and ion release tests were carried out to evaluate the feasibility of laser welded joint crystallization in the biomedical field.The corrosion resistance relationship between the base metal and the welded joint was judged by detecting the electrochemical experiments of the welded joint with good performance and low crystallization rate and the base metal in Ringer’s solution.The typical laser welded joint between the base metal and Zr-based amorphous alloy was immersed in Ringer’s solution at 37℃for a period of time,and the metal ion concentration in the solution was detected by Inductively coupled plasma mass spectrometry（ICP-MS）to evaluate the ion release rate and safety,the Ni ion concentrations released by the base metal and typical laser welded joints are 4×10^-6 mg/L and 3×10^-6 mg/L,respectively,which are within the safety range.It is proved by experiments that a small amount of nanocrystals is beneficial to improve the corrosion resistance of amorphous alloys.