Effect And Law Of Pulsating Age-Hardening Of 2219 Aluminum Alloy Friction Stir Welding Weld

2219 aluminum alloy has high strength and good performance at low temperatures,which is widely used in the aerospace field.Friction stir welding is the main welding process of large aerospace components,and the high temperature during thermal cycling in the welding process causes the reinforced phases re-dissolving into the aluminum matrix,resulting in a serious decline in welding strength.In view of the problems of large-scale components such as large thermal deformation of the overall artificial aging components,the over-aging of the base material and the absence of oversized uniform heating devices,the paper proposes a pulsating aging process method: the weld is heated to the aging temperature in a short period of time by locally moving the heat source,and then it is quickly cooled to room temperature,and the aging new process accumulated many times is cycled.In this paper,using oil bath as heat source,the feasibility and regularity of the new pulsating aging process was studied by using solid solution 2219 aluminum alloy with good homogeneity compared with friction stir welding.Then,the 2219-T6 aluminum alloy friction stir weld of heterogeneous body is controlled to be heated by pulsation in oil bath to simulate the local pulsating aging process of aerospace large-scale weld components,which provides a theoretical basis for the research on the local pulsating aging treatment of aerospace large-scale weld components.The main research work of this paper is as follows:(1)The experimental study on pulsating aging strengthening of 2219 aluminum alloy was carried out.The results showed that when the temperature was 165℃,the mechanical properties of 2219 aluminum alloy in solid solution state were significantly improved under the decreasing periodic parameter aging experiment.The improvement degree was independent of the period time,but the cumulative times of reaching the peak mechanical properties were different.Pulsating aging equivalent 16 h,solid solution state 2219 aluminum alloy reach the biggest microhardness145 HV,the maximum tensile strength was 445 MPa,the same time as continuous aging to peak aging state,pulsating aging strengthening effect compared to continuous aging without obvious "delay" phenomenon.After the pulsating aging treatment,the fracture morphology of 2219 aluminum alloy in solution state changed obviously,which verified the feasibility of pulsating aging together with the change of mechanical properties.(2)A comprehensive experiment of two factors and three levels of rotation speed and welding speed was designed.Friction stir welding model was established based on DEFORM-3D software,and 9 groups of welding process parameters were simulated and analyzed by finite element method.The simulation results showed that when the welding process parameters were n=1000rpm and v =300mm/min,the center temperature was basically around 480℃,which was close to the highest thermal cycle temperature with better re-dissolution of the strengthened phase.There was a certain gap between the other 8 groups of welding process parameters and the optimal welding temperature.The simulation results were in good agreement with the measured results,which could be used to optimize the welding process for pulsating aging.(3)Pulsating ageing experiments of stir friction welds were carried out after optimizing the process parameters.The results showed that the mechanical properties of the center area of the weld improved the most after pulsating aging treatment.The further away from the center area of the weld,the less the improvement.The mechanical properties of the retreating side was lower than that of the advancing side.The welded tensile strength of the weld was 310 MPa,and the mechanical properties improved the fastest after the pulsating aging for equivalent 2h,which was347 MPa.The peak aging tensile strength was 371 MPa after pulsating aging for equivalent 12 h.The pitting resistance of weld decreased after pulsating aging,and the pitting resistance of weld core was stronger than that of heat affected zone.After the high temperature of thermal cycling of about480°C,both θ and θ were dissolved into aluminum matrix,new θand θ were precipitated after pulsating aging for equivalent 2h.After the pulsating aging for equivalent 12 h,the second phase fully precipitated and reached the peak aging state.