The Research Of Microstructure Property And Fluidity Visualization On Fsw Joint With Dissimilar Heat Treatment 6061 Aluminum Alloys

6061 Aluminum alloy is one of the most common kinds of 6000 series Aluminum alloys,which is widely used in various fields of industry.As a new kind of Solid-phase welding,FSW provides a new way for us to product efficient and quality Aluminum alloy joints.But,scholars are still seeking for the flow patterns and forming mechanism of FSW weld joint metal,there is no authoritative conclusion in academic so far.So it is significant for us to find the way to research it.In this paper,6061-T6 and 6061-O aluminum alloy are selected as the experiment objects to create different butt joints.After welding experiment,the writer analyzed the microstructure and property of each joint.The writer also studied the characteristics of metal flow in different heat treatment state 6061 Aluminum alloy FSW joints with marking& tracing method.Marking & tracing method is a common method to research the visualization of flow characteristics.It is an effective and intuitive method to choose copper powder and copper foil being the marking material for observing the plastic formation in FSW joint.At the result of tensile test,O-O joint and O-T6 joint belong to plastic fracture,T6-T6 joint belongs to quasi-cleavage fracture.The micro-hardness curve of T6-T6 joint assumes“W” shapes,the hardness of NZ reaches 70% of BM.The curve of O-O joint was parabola;the maximum hardness appears in NZ,which reaches 125% of BM.The micro-hardness curves of T6-O and O-T6 are mirror inversion,but there are also several differences between them.In terms of microstructure,NZ has Fine equiaxed grains,which sizes are3-5?m.Second-phase particles distribution in the middle of grain,the chemical composition is Mg2 Si.The grains in TMAZ were elongated to strip shape.The grains in SAZ have the least sizes,because of the fast speed of heat dissipation in dynamic recrystallization process.Thread on the pin provides a vertical dynamic to motivate the plastic metal flowing to a lower level.The plastic metal on lower level will not transfer back to a higher level.The plastic metal on higher level has stronger liquidity that can transfer to a farther area in both vertical and horizontal directions.In horizontal direction,thread pin carries the plastic metal to rotate several cycles;the pin without thread carries the plastic metal to rotate only half cycle.Metal in NZ comes primarily from the base material in advantage side,these plastic metal flows down to a lower level.Then the plastic metal in retreating side move round the NZ and reach the cavity above it.Firstly,base material in advantage side transfer into theNZ;they have suffered severe plastic distortion.Material in retreating side transfer later into NZ;they have just suffered slight plastic distortion.Metal in SAZ comes primarily from the base material in retreating side.When AA6061-O locates in the retreating side,the plastic metal in SAZ flows violently and transfers distantly.When AA6061-T6 locates in retreating side,the plastic metal in SAZ flows more slowly.The size of TMAZ in 6061-O side is wider then that in 6061-T6 relatively.