Texture Evolutions In Friction Stir Welding 5083-H321 Aluminum Alloy Plates

The 5083-H321 aluminum alloy plates were welded by friction stir welding(FSW) technology. The grain morphology and metal flow of different welding seam zones were fully analyzed by OM, continuously shooting and seamless montage technology. The sub-grain, second phase and dislocation of different welding seam zones were analyzed by TEM and compared with those of BM. For the SEM, EBSD and OIM technology, the grain morphology, grain boundary and grain orientation of each zone for FSW welding seam was studied. Meanwhile, base on theories of heat distribution and metal flow during FSW, texture evolution of 5083-H321 aluminum in FSW welding seam was discussed. The main results are as follows:1. The grain characteristic of different welding seam zones for FSW-5083 was investigated. The grains morphology of base metal(BM) is banding. And there are lots of dislocations and substructures inner grain. After friction stir welding, some grains of heat affected zone(HAZ) growed and the content of LAGB decreased. However, the grains morphology is still banding. Grains in thermo-mechanical affected zone(TMAZ) also retain the morphology of grains in BM. Nevertheless, there is an angle between grains elongate direction and rolling direction. The LAGB content of TMAZ is less. And grains in nugget zone(NZ) are equiaxial. The content of LAGB is lowest in the whole welding seam. The variation of average grain size(d) for those welding seam zones and BM is dHAZ>dBM> dTMAZ>dNZ.And the variation of LAGB(V) for those welding seam zones and BM is VBM> VTMAZ> VHAZ>VNZ.2. The microstructure characteristic and effects of different zones of FSW nugget zone were investigated. Although there are equiaxial grains in NZ, the microstructure is slightly different in the centre and the both sides of NZ. The variation of average grain size(d) for nugget advancing side(NAS), nugget median zone(NMZ) and nugget retreating side(NRS) is dNAS>dNMz> dNRS.And the variation of LAGB(V) for NAS, NMZ and NRS is VBM> VTMAZ >VNZ>VNZ.The dynamic recrystallization which was caused by high temperature is the basic reason for the equiaxial grains created in NZ. And the heterogeneous temperature distribution which was caused by the complex metal flow in NZ is the important reason for the creation of heterogeneous microstructure.3. The crystal orentation characteristics of different welding seam zones were investigated. The<110> and<111> of base mental tend to gather together on the [001] and [010] direction of specimen coordinate system, respectively. Although the grain orentation of HAZ is similar to BM after FSW, the orentation intensity reduced. The<110> and<111> direction of TMAZ tend to gather together on the [001] and [010] direction of specimen coordinate system, respectively. And the orentation intensity is strong. Meanwhile, the orentation of NZ is not obvious. These crystal orientation changes mean that HAZ retains part orientations of BM, while crystal orientation of TMAZ and NZ change greatly after friction stir welding.4. Texture characteristic of different welding seam zones was investigated. BM textures are mainly consisted of Brass{011}<211> and S{123}<634>, their area percentages are 28.2% and 13%, respectively. HAZ textues are mainly{149}<511> and{236}<385>, their area fractions are 11.6% and 10.8%, respectively. However, the B{011}<211> area fraction is only 6.2%. Meanwhile, TMAZ texture are mainly{112}<111> and{112}<132>, their area fractions are 16.4% and 8.3%, respectively. In addition, the area fractions of textures which are frequently observed in face-centered cubic metal were weak in the NZ, these area fractions are all below 5.1%.5. The variation characteristic of α and β orientation line of different welding seam zones for 5083 aluminum in the orentation space was investigated. The density of B which is in the middle location of BM a orientation line is the strongest, but the density on the both ends is low and the curve changs gradually. The a cuve of HAZ is similar to it of BM. However, all of these density values are lower than it on the same location of BM. The orientation density changs of a cuve for TMAZ and NZ are gradual, and the values are low. Meanwhile, the orientation density of BM β orientation line increased as Φ2 increased. And the B orientation density is the highest on BM β orientation line. The variation of HAZ β orientation line is similar to BM, but all of these density values are lower than it on the same location of BM. However, the change of TMAZβ orientation line is contrary to BM, the density of C orientation is the highest. Meanwhile, the density change of NZ β orientation line is stable and the values are low. These changes of α and β orientation line mean that HAZ retains part textures of BM, while textures of TMAZ and NZ change greatly after friction stir welding.6. Base on theories of heat distribution and metal flow during FSW, texture evolution of 5083-H321 aluminum in different welding seam zones was discussed. During FSW, the unhomogeneous temperature distribution of different welding seam zones is the main reason for the evolution of recrystallization texture in different welding seam zones. The recovery or recrystallization is different due for different tempreture, and that the texture content changes. The area fractions relation of mainly recrystallization textures for different welding seam zones and BM is SHAZ> SBM> SNZ> STMAZ.Meanwhile, the different deformation direction or degree is the main reason of the content change for deformation texture of different welding seam zones. The area fractions relation of mainly deformation textures for different welding seam zones and BM is SBM> STMAZ> SHNZ>...