| With the development of the transportation industry,the energy crisis is becoming more and more serious.Because of its small density,high specific strength,corrosion resistance,good molding performance and so on,aluminum alloy is widely used in train body.Friction stir welding of aluminum alloy can solve the difficult problem of aluminum alloy welding.The 6082-T6 aluminum alloy used in the test is more and more widely used in transportation and mechanical engineering because of its good weldability,excellent mechanical properties and corrosion resistance.Microstructure and mechanical proprieties of friction stir welded 6082-T6 aluminum alloy were layered-investigated by means of transmission electron microscope(TEM),using scanning electron microscopy(SEM)analysis of welded joint fracture,combined with microstructure changes on the tensile strength and hardness change analysis.The results showed that 6082-T6 aluminum alloy FSW joint of upper and lower weld microstructure chan ged,regional precipitation phase respectively were that: the parent material has mainly " β" ";the weld nugget has GP zone and small size of Fe Si2;The heat affected zone has" β’ ".Due to the heat input,each region has undergone dynamic recovery and dynamic recrystallization in different degrees.The microhardness curve was similar to the " W " shape;the minimum value appeared in the advancing side of the heat affected zone.The tensile strength of the weld zone was 72% of the base metal,and the tensile strength of the upper weld zone was higher than that of the bottom weld.6082-T6 FSW aluminum alloy joint ahead of the keyhole contained β",behind of the keyhole was Fe Si2 precipitates.The microhardness of the longitudinal section of the 6082-T6 aluminum alloy joint was larger changed that the microhardness ahead of the keyhole was larger than that of the behind of the keyhole.The hardness of the welded joint increased gradually from the bottom to the upper part of the joint,and the softening zone of the heat affected zone was gradually enlarged.The tensile properties of 6082-T6 aluminum alloy friction stir welding joint were the highest ahead of the keyhole,and the inclusions in each region contain the phase.The fracture mode in different regions were typical ductile fracture.The friction stir welding joint of 6082-T6 aluminum alloy was treated by natural aging and artificial aging in the aspects of low tensile strength and poor mechanical properties,the results showed that microhardness after artificial aging treatment was higher than welded and natural aging about 10-25 HV,the effect of microhardness for nugget zone and heat affected zone higher than natural aging.After post weld natural aging、artificial aging treatment of welded joint mechanical properties was improved to a certain extent,artificial aging treatment was compared to natural aging treatment after tensile strength increased by 12%,elongation decreased by 9% and the effect of artificial aging improve tensile strength was more obvious.Because the microstructure of aluminum alloy FSW joints was not uniform,the same weld may occur a variety of corrosion types,by observing the microstructure of the FSW alloy after corrosion,and combining with the electrochemical test found that the corrosion resistance weld in the middle of weld was optimum and base material inferior to the behind of the tool and ahead of the tool.Corrosion type of 6082-T6 aluminum alloy was mainly intergranular corrosion and spalling corrosion of base material,ahead of the tool,behind of the tool,and with the increase of time the degree was gradually speeded.The corrosion weld in the middle of weld ha d not been observed. |
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