Experimental Study And Finite Element Simulation Of Refill Friction Stir Spot Welding Process

In this paper,in order to study the effects of different process parameters on mechanical properties and microstructure of joints,the refill FSpW lap joining experiments of 2.4 mm thick 5A06 aluminum alloy and 3 mm thick AZ31 magnesium alloy were conducted respectively.Thermo-mechanical coupled model of refill FSpW of aluminum alloy and magnesium alloy was established respectively,and temperature field,material flow and material deformation behavior during refill FSpW process were studied.In order to study the effects of different process parameters(stiring tool rotation speed,plunging time and refill time)on refill FSpW lap joint's performance of 5A06 aluminum alloy sheet,orthogonal experiment was designed.The tensile shear properties of the joint were tested to determine the order of the factors and obtain the optimal parameters.The results show that the influence of the refill time on the tensile load of the joint is the most important,followed by rotation speed and plunging time successively.Under the optimum parameters,(the refill time is 1 s,rotation speed is 1500 r/min and plunging time is 2 s),the tensile load of the joint can reach 11.683 k N.Refill FSpW experiments on AZ31 magnesium alloy sheet were conducted in order to study the effect of different process parameters on Hook defects.The results show that the joints of longer welding time and higher heat input have lower Hook height,thereby the joint undergoes sufficient dynamic recrystallization and metallurgical bonding.Thermo-mechanical coupled model of the refill FSpW process of 5A06 aluminum alloy was established.The temperature in the stir zone is the highest,and the material flow rate in the cavity is the highest.It is proposed to study the interface migration by using point tracking technique,wherein a series of points with different horizontal coordinates align to the virtual interface.The results show that the virtual interface center corresponding to the cavity rises firstly and then falls.In order to study the interface migration and Hook defect evolution,refill FSpW model is modified that two plates correspond to separate blocks.The interface experiences reverse migration in the plunging phase and refilling phase.During the plunging phase,the interface height is gradually increasing,and the growth rate of interface is gradually increasing.The interfacial height gradually decreases during the refilling phase,and the velocity is generally stable.The Hook defect is formed during the refilling phase,the Hook height gradually increases with time.The Hook height grows more and more slowly,and reaches a maximum at the end of the refilling process.