The detailed precipitation behavior and grain structure in different sub-regions of friction stir welding(FSW)AA6061-T6 joint after post-weld solution and aging treatments were explored.And the effects of microstructu...The detailed precipitation behavior and grain structure in different sub-regions of friction stir welding(FSW)AA6061-T6 joint after post-weld solution and aging treatments were explored.And the effects of microstructural evolution on mechanical properties,macro/micro electrochemical corrosion behavior and stress corrosion cracking behavior were investigated.The inherent microstructural gradients in FSW joint lead to dramatic degradation of mechanical properties and the presence of macro-galvanic effect,with the latter exacerbating anodic dissolution in heat-affected zone(HAZ)induced by micro-galvanic corro-sion and inhibiting pitting corrosion in stirred zone(SZ).Post-weld heat treatment(PWHT)causes the formation of matrix precipitates with similar densities in different sub-regions,resulting in optimized precipitate distribution,comprehensive hardness recovery,and diminished macro-galvanic effect.Grain boundary misorientation angle,grain size and pre-existing dislocations synergistically influence the evo-lution of grain boundary precipitates(GBPs)and precipitation-free zones(PFZs)during the PWHT.As a result,pitting corrosion is the dominant corrosion form in SZ due to the narrowest PFZ width and dis-persed GBPs,while intergranular corrosion is caused by continuous GBPs in other sub-regions.This study verified the dominant role of macro-galvanic effect and micro-galvanic effect in the corrosion process of FSW joint and FSW-PWHT joint,respectively.The maximum SCC susceptibility at HAZ in As-FSWed joint is dominated by enhanced anodic dissolution due to macro-galvanic effect.The SCC sensitivity of FSW-PWHT joint is higher than that of FSW joint due to high electrochemical activity and corrosion rate caused by the severe stress concentration between sub-grains and recrystallized grains at the thermome-chanical affected zone(TMAZ)/SZ interface.展开更多
The corrosion fatigue fracture mechanism of friction stir welding(FSW) joints of 7075 aluminium alloy in3.5% NaCl solution is investigated. The corrosion fatigue crack source originates from the junction of nugget zon...The corrosion fatigue fracture mechanism of friction stir welding(FSW) joints of 7075 aluminium alloy in3.5% NaCl solution is investigated. The corrosion fatigue crack source originates from the junction of nugget zone(NZ)and thermo-mechanical affected zone(TMAZ). Multiple crack sources are developed at the same time, and they merge into large cracks along the boundary line of NZ and TMAZ during the propagation stage. Furthermore, a mutual reinforcement coupling always exists between corrosion and cyclic loading during the initiation and propagation of corrosion fatigue crack. It is necessary to consider the effect of welding residual stress for understanding the mechanism of corrosion fatigue fracture of FSW joints.展开更多
基金supported by the National Key R&D Program of China(No.2022YFB3705801)the National Natural Science Foundation of China(No.52271065).
文摘The detailed precipitation behavior and grain structure in different sub-regions of friction stir welding(FSW)AA6061-T6 joint after post-weld solution and aging treatments were explored.And the effects of microstructural evolution on mechanical properties,macro/micro electrochemical corrosion behavior and stress corrosion cracking behavior were investigated.The inherent microstructural gradients in FSW joint lead to dramatic degradation of mechanical properties and the presence of macro-galvanic effect,with the latter exacerbating anodic dissolution in heat-affected zone(HAZ)induced by micro-galvanic corro-sion and inhibiting pitting corrosion in stirred zone(SZ).Post-weld heat treatment(PWHT)causes the formation of matrix precipitates with similar densities in different sub-regions,resulting in optimized precipitate distribution,comprehensive hardness recovery,and diminished macro-galvanic effect.Grain boundary misorientation angle,grain size and pre-existing dislocations synergistically influence the evo-lution of grain boundary precipitates(GBPs)and precipitation-free zones(PFZs)during the PWHT.As a result,pitting corrosion is the dominant corrosion form in SZ due to the narrowest PFZ width and dis-persed GBPs,while intergranular corrosion is caused by continuous GBPs in other sub-regions.This study verified the dominant role of macro-galvanic effect and micro-galvanic effect in the corrosion process of FSW joint and FSW-PWHT joint,respectively.The maximum SCC susceptibility at HAZ in As-FSWed joint is dominated by enhanced anodic dissolution due to macro-galvanic effect.The SCC sensitivity of FSW-PWHT joint is higher than that of FSW joint due to high electrochemical activity and corrosion rate caused by the severe stress concentration between sub-grains and recrystallized grains at the thermome-chanical affected zone(TMAZ)/SZ interface.
基金Project(KYGYJQZL2204) supported by the Basic Frontier Science and Technology Innovation Project of Army Engineering University of PLA,ChinaProjects(30110010403, 30110030103) supported by the Preliminary Research of Equipment,China。
文摘The corrosion fatigue fracture mechanism of friction stir welding(FSW) joints of 7075 aluminium alloy in3.5% NaCl solution is investigated. The corrosion fatigue crack source originates from the junction of nugget zone(NZ)and thermo-mechanical affected zone(TMAZ). Multiple crack sources are developed at the same time, and they merge into large cracks along the boundary line of NZ and TMAZ during the propagation stage. Furthermore, a mutual reinforcement coupling always exists between corrosion and cyclic loading during the initiation and propagation of corrosion fatigue crack. It is necessary to consider the effect of welding residual stress for understanding the mechanism of corrosion fatigue fracture of FSW joints.
