| Due to the uniform microstructure,fine grains,excellent strength and toughness of spray-formed 7055 aluminum alloy,it has been widely used in industries.When this alloy was connected by fusion welding,the microstructure of weld metal（WM）is coarse dendrites.The hot crack sensitivity of fusion weld joints is high.In addition,the mechanical properties of fusion weld joints are much lower than the base metal,which cannot satisfy the requirement of application.Although the hot crack sensitivity of fusion weld joints could be modified by the adjusting of welding parameters,the microstructure and properties are still cannot meet the standards for application.Therefore,it is necessary to fabricate new filler rods.Based on the excellent properties of TiB2 ceramic particles and the element of 7055 aluminum alloy,TiB2-Al3Ti modified filler rods were fabricated by the mixed-salt（MS）and master alloy（MA）methods,and used for the TIG welding of spray formed 7055 aluminum alloy.The effects of two fabrication methods on the microstructure and properties of weld joints were studied.In addition,the heat treatments of weld joints were further investigated.The main results are as follows:（1）The distribution of TiB2 fabricated by two different methods on theα-Al matrix and the effect of TiB2 on the microstructure and properties of alloys.The results show that TiB2ceramic particles in MS filler rods are uniformly distributed.There is only a small part of clusters.However,there is no TiB2 clusters in MA filler rods.In addition,there are some ringlike Al3Ti phase in MA filler rods.Compared with the as-cast 7055 aluminum alloy,the microstructure and mechanical properties of ceramic particle reinforced filler rods are better.（2）7055 base metal,MS and MA filler rods are used for the TIG welding of spray-formed 7055 aluminum alloy,and the microstructure and mechanical properties of the three kinds of WM in the as-welded state have been investigated.The results show that:（a）The distribution of the reinforced particles has not changed.The microstructure of WM transfers from coarse dendrites to fine equiaxed crystals.The introduction of ceramic particles reduces the segregation of alloying elements in the WM,and modifies the hot crack susceptibility of weld joints.The analyses of XRD and TEM show that the reinforced particles of the MS joint are TiB2,and the reinforced particles of the MA joint are TiB2 and Al3Ti.（b）The mechanical properties of weld joints have been effectively improved.The tensile strength and elongation of as-welded joints increase from 240±5 MPa,1.79±0.24%（7055）to 313±6 MPa,5.64±0.24%（MS）and 284±7 MPa,4.0±0.35%（MA）,respectively（7055）.There are no brittle Al3Ti phases in MS joints.Therefore,the mechanical properties of MS joints are better than MA joints.（3）Three kinds of joints have been subjected to heat treatments.The microstructure,mechanical properties and corrosion resistance of the three joints with different aging treatments have been investigated.The results show that:（a）The distribution of TiB2 and Al3Ti has not changed,and they can limit the growth of WM grains.（b）With the same aging treatment,the strength of MS joints is still better than MA joints.The strength of 7055 joints is the worst.In the same weld joints,the strength with the T6 treatment is the highest,the RRA treatment is followed,and the T76 treatment is the lowest.Compared with the as-welded state,the elongation of the three joints has decreased.The tensile properties of MS and MA joints are still better than those of 7055.（c）The electrochemical tests show that the corrosion resistance of MS and MA WM are similar,but both them are better than 7055-WM.The corrosion resistance of the same kind of joints are as follows:T76>RRA>T6.The TEM analysis shows that the GBPs of WM with the T6 treatment are continuous,while the GBPs of T76 and RRA are discontinuous.The discontinuous GBPs interrupt the paths of intergranular corrosion and delay the process of corrosion. |
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