Study On Stress Relaxation Behavior Of 7075 Aluminum Alloy Friction Stir Welded Component

The structural design of modern aircraft has many classes.Among them,the structure of integral panel is the most widely used,and the friction stir welding of FSW as a new way greatly reduces the manufacturing cost of integral panel,so the study of aging welding panel forming has good application prospects.There are many factors affecting the age forming,and stress relaxation behavior of materials is the foundation deformation age forming,its component determines the final shape and precision.Therefore,research on the stress relaxation behavior of the 7075 Aluminum Alloy FSW component can provide a basis for analysis of the forming mechanism of weld panels aging.Basing on the analysis of stress relaxation behavior of the 7075 Aluminum Alloy,focusing on the welded joints in different regions of the organization characteristics of the stress relaxation behavior was characterized,discussed effect of forming stress relaxation behavior of welded joints aging nonuniformity.this paper comparative studys the influence of the members of the weld stress relaxation behavior,analysis stress relaxation of the creep temperature and pre deformation parameters under the law,and through optical microscope(OM),scanning electron microscopy(SEM),transmission electron microscopy(TEM)systematic analysis the results.The results show that the stress relaxation behavior of the 7075 aluminum alloy is similar to that of the traditional stress relaxation behavior,which is a logarithmic curve.But the stress relaxation process can be divided into three stages: in the initial stage,the stress decreased rapidly;the mid transition phase,the stress decreased slowly;in the later stage of stress relaxation,stress remained unchanged,and ultimately achieve the stress relaxation limit.It is found that the effect of creep temperature on stress relaxation behavior is much larger than that of pre deformation.When the temperature is high,the initial stress relaxation rate is high,with the increase in stress relaxation time,stress decreased rapidly,the stress relaxation rate decreased greatly.After a period of stress relaxation,the temperature is high,the stress relaxation rate is even less than the condition of low temperature.In the final stage of force relaxation,the stress relaxation rate of the specimen with creep aging temperature of 200 DEGC is higher than that of the sample at 160 DEGC,and the stress relaxation limit is reached at early time.The weld nugget hardness(WN)is located in the base area(BM)and lower thanthat of the heat affected zone(HAZ).With the increase of creep aging temperature,the hardness of the base area and the heat affected zone of the FSW component decreased.the weld nugget zone(WN)hardness of irregular change,metallographic analysis has no obvious regularity.Metallo graphic analysis shows that in the TMAZ with increasing creep aging temperature,black phase gradually increased.And the welding area did not change significantly with the increase of aging temperature,there are still black aggregates,and no obvious change.Scanning electron microscopy analysis showed that the shape of the material is rolling,which results in the hardening of the parent material,which leads to a large number of dislocations in the parent material zone.The thermal cycle of the heat affected zone is not enough to cause the second phase to dissolve,and the growth and coarsening of the second phase occurs under the action of heat.