Process And Joining Mechanism Of Dissimilar Materials Ti/Al Butted Joint By Friction Stir Welding

TC4titanium alloy and5A06aluminum alloy were successfully butt-joined by friction stir welding(FSW) utilizing a special design of butt-joint configuration in this acticle. The aluminum meltingphenomenon was effectively inhibited, and a good-formability and high-quality Ti/Al composite jointcould be obtained in the experiment.Based on the cylindrical milling stir tool, the article analyzed the weld surface morphology,interface microstructure, mechanical properties and fracture morphology of Ti/Al composite joints,and set up the best welding parameters window. The experiment results showed that the weldingformability and interface microstructure were greatly affected by the rotation speed n, the weldingspeed v and the pin offset T. The pin offset design resulted in a aluminum matrix compositeorganization reinforced by titanium particles at the stir nugget zone (SNZ). The maximum averagetensile strength of Ti/Al composite joints reached88.3%of that of5A06aluminum alloy, and thefacture occurred mainly on the aluminum side at SNZ.The effect of pin offset on the macro/microstructure and mechanical properties of Ti/Al compositejoints based on the circular smooth-surface stir tool were analyzed. A vortex flow, a turbulent flow anda Hook structure were found at the SNZ. Changing the pin offset could effectively control the heatinput during FSW process and avoid the generation of intermetalic compounds or holes at the buttinterface. Relative to the cylindrical milling stir tool, the welding parameters window corresponding tothe circular smooth-surface stir tool was wider. The maximum average tensile strength of Ti/Alcomposite joints reached84.1%of that of5A06aluminum alloy, and the facture also occurred on thealuminum side at SNZ. The fracture surface showed a composite morphology of dimples and cleavagesurfaces.Combined the experiment results above, the article analyzed the thermal-mechanical coupling effect,the inhibition mechanism of aluminum melting phenomenon, the macro deformation behavior ontitanium side, the composition gradient. The analysis found that the aluminum melting phenomenonand intermetallic compounds could be effectively inhibited by using reasonable process parameters.Ti/Al atomic diffusion occurred at the interface and resulted in a diffusion layer with a thickness of2~3μm. Ultimately Ti/Al dissimilar welds with good formabilities and high qualities could be achieved.