Microstructure And Mechanical Properties Of Friction Stir Welded Joint Of Zr-based Bulk Metallic Glass With Pure Aluminium

Due to the high strength and superior wear and corrosion resistance, bulk metalliclasses （BMG） have a great potential application as a kind of new structural materials.However, most current homogeneous glassy BMGs are too small to structuralapplications. In order to extend the engineering applications of BMGs, weldingtechnologies also need to be developed. More over, the possibility of joining BMGs withthemselves or crystalline materials is desirable to integrate the metallic glass componentsinto the structure of machines or other products. In this thesis, two kinds of Zr-basedBMGs (Zr₆₅Cu₂₀Al₁₀Fe₅and Zr₄₆Cu₄₆A_l8) and commercial pure aluminum were subjectedto friction stir welding （FSW） to investigate the weld ability of these dissimilar materials.The microstructure evolution at the welding region during the welding and themechanical properties of the joints was investigated. The influences of the stirring pinwalking speed and the composition of the Zr-based BMGs on the friction stir weldingproperty was discussed.（1） Zr₆₅Cu₂₀Al₁₀Fe₅and Zr₄₆Cu₄₆A_l8are successfully jointed with pure Al by FSWmethod under the1500rad/min rotation speed of the stirring pin and75mm/min and150mm/min walking speed of the workpiece. A clear interface is observed between the BMGand pure Al, and no defects are detected in the joint indicating that the sound joining isachieved between the BMG and pure Al by FSW.（2） The microstructure evolution at the welding zone during welding wasinvestigated. The results indicated that, during FSW, the BMG matrix was notcrystallized, but some amorphous debris were stirred into the welding zone close to thepure Al. The amorphous debris reacted with aluminum to produce aluminum-rich phases.The walking speed of the workpiece has an important effect on the microstructure andmechanical properties of the joints. For the Zr₄₆Cu₄₆A_l8/Al joint, relatively slow walkingspeed of the workpiece can produce a thorough stirring, which led to the formation of thesmall and disperse amorphous particles in the welding zone. Thus, the joint ofZr₄₆Cu₄₆A_l8/Al obtained under a walking speed of75mm/min exhibits a relative hightensile strength, which reaches90%of that of the Al substrate.（3） The composition of the Zr-based BMGs also has an important effect on the FSWperformance. In comparison with Zr₄₆Cu₄₆A_l8, Zr₆₅Cu₂₀Al₁₀Fe₅has a lower glasstransition temperature and crystallization temperature. During FSW, more amorphousfragments were stirred into the welding zone, Therefore, under the same conditions, the joint of Zr₆₅Cu₂₀Al₁₀Fe₅/Al showed a lower tensile strength than that of the joint ofZr46Cu46Al8/Al.