Study On The Mechanism Of Laser Welding Of Zr-based Bulk Metallic Glass

Bulk metallic glasses have been applied in electronic industry, mechanicalengineering, chemical engineering, biomedical and aerospace fields, due to its highstrength, wear resistance, corrosion resistance, good biocompatibility, excellent softmagnetic properties and low magnetic loss. With the further development of researches ofbulk metallic glasses, their engineering application will be more extensive. In theengineering application field, the joining of bulk metallic glasses is an unavoidable issue,regarding which welding should be particularly emphasized.In this article, pulsed laser irradiation was conducted statically to heat up theZr_53.7Ni_9.4Cu_28.5Al_8.4bulk metallic glass. The microstructures and morphologies of thegrains in the joint, the evolutions of the constituting of the joint and crystallizationbehavior were systematical analyzed. The results indicated that HAZ was liable tocrystallize more easily compared with the MZ. The crystallization mechanisms in the MZand HAZ are different. Crystallization in MZ highly depends on the glass formation ability（GFA） of bulk metallic glass. Regarding the HAZ, crystallization in this area depends onthe thermal stability of bulk metallic glass. According to the finite element numericallysimulating of the temperature field of the bulk metallic glass during laser irradiationprocess, the thermal cycles of MZ and HAZ had been obtained, based on which thedifferent crystallization behaviors were explained. Then the critical retention time（including heating time and cooling time） in the crystallization temperature range of theHAZ, as a criterion, was estimated to determine whether a crystallization-free HAZ wasproduced.Subsequently, this study selected fiber laser to weld Zr_53.7Ni_9.4Cu_28.5Al_8.4bulk metallicglass and investigated the effects of laser peak power and welding speed on themicrostructure development in the welded joint. The crystallization behavior in the weldmetal and the HAZ were discussed during the thermal cycle of the laser welding process.Under the process condition of laser output power1200W, spot diameter0.3mm, defocusddistance0, welding speed30m/min, precipitates of about4μm were still produced in HAZ. By calculating the heating and cooling retention time in the crystallization temperaturerange of the critical crystallization spot of the HAZ, and comparing it with the criticalretention time of the bulk metallic glass, the correctness of the critical retention timecriterion was initially validated.