Laser Welding Forming And Crystallization Control Of Zr Based Amorphous Alloy

Zr-based amorphous alloys have been widely used in 3C consumer electronic products,sports equipment and other fields because of their good glass forming ability,large elastic modulus,high strength,hardness and excellent corrosion resistance.However,the problems such as small size,single structure and difficult machining of amorphous alloys have been limited in the application of engineering.As an efficient method of intermetallic connection,welding was one of the effective ways to solve the application problems of amorphous alloy Therefore,in this paper,the Zr-based amorphous alloy with good amorphous forming ability was taken as the research object,and laser welding was selected to carry out welding experiments.The influence of laser welding parameters on the formation of microstructure and properties of welded joint was studied systematically,and the control conditions of crystallization were exploredIn this paper,Zr67.8Cu24.7A13.43Ni4.07 and Zr58Nb2.76Cu15.46Ni12.74Al10.34Y0.5 amorphous alloys were used as welding materials.The crystallization curves of the two materials were measured by differential scanning calorimeter(DSC),and the glass forming ability and stability were studied.Aiming at the problems of small size,poor thermal stability and easy combination with O,N and other elements,the sample cooling fixture and welding protective hood were designed.Through the experimental comparison,the protective effect of the optimized design of the protective device on the welding seam had been significantly improved.The welding experiments of Zr67.8Cu24.7Al3.43Ni4.07 amorphous alloy were carried out by controlling the welding speed and laser power respectively.When the laser power was 600 W and the welding speed was 110 mm/s,a better welding joint was obtained,and the crystallization rate was only 2.4%.After welding,the crystallization of the joint mainly occurs in the heat affected zone,and the base material around the weld zone and the joint basically remains amorphous.High laser power welding was conducive to the realization of deep penetration welding,so that the joint was completely connected,but it was easy to intensify the crystallization of the joint;high welding speed can further improve the heating and cooling rate of the welding,so as to effectively inhibit the crystallization phenomenon,but high welding speed will reduce the heat input,leading to the failure of the connection.Welding experiments were carried out on Zr58Nb2.76Cu15.46Ni12.74Al10.34Y0.5 amorphous alloy at 1200 W,3000 W and 4500 W laser power,respectively.The results showed that the influence of welding speed on the formation of joint morphology was consistent under various laser power The welding joint with narrow melting width and low crystallization rate can be easily obtained under high power and high welding speedDue to the different thermal effects of thermal cycle and thermal accumulation,crystallization mainly occurs at the bottom of the heat affected zone,and the crystallization degree of the middle and upper part was weak.The grains near the base metal side of the heat affected zone were small but the number was large,while the grains near the weld side were large but the number was small.Calibration by X-ray diffractometer and transmission electron microscopy showed that the crystallized precipitate in the heat affected zone of Zr67.8Cu24.7Al3.43Ni4.07 amorphous alloy was CuZr phase.The hardness of the heat affected zone decreased obviously due to the serious crystallization,and the hardness of the weld zone was slightly higher than that of the base metal due to the gain effect of the nanocrystalline.The crystallization precipitate in heat affected zone of Zr58Nb2.76Cu15.46Ni12.74Al10.34Y0.5 amorphous alloy was NiZr2 phase.As NiZr2 can improve the hardness of the material,the hardness of the heat affected zone was significantly higher than that of other areas,and the hardness of the weld zone was basically the same as that of the base metal.When the laser power was 600 W and the welding speed was 110 mm/s,the crystallizing rate of the joint of Zr67.8Cu24.7Al3.43Ni4.07 amorphous alloy was the lowest,its tensile strength was 1247 MPa,about 91%of the base metal.