Study on the texture, residual stress and mechanical properties of 7039-T6 thick plate aluminum alloy with MIG welded laminar tearing

7039 aluminum alloy is widely used in the vehicle armor field due to its high specific strength and fracture toughness. However, laminar tearing in the thickness plane of the base metal (BM), i.e., the normal direction (ND) - rolling direction (RD) plane, was occasionally found after welding of thick plates, resulting in premature failure of the material. In order to find out the reason for this, a vertically metal-inert gas (MIG) welded laminar tearing part of a 30 mm thick plate was analyzed. The texture, residual stress, microhardness and tensile properties were investigated. The results indicated that the crack extended along the RD as transcrystalline fracture and terminated at the BM. The grains near the crack grew preferentially in the (001) crystal direction. Furthermore, the tensile strength (83 MPa) and elongation (6.8%) in the RD were relatively higher than the ND. In particular, stronger texture, higher dislocation density, more Al7Cu2Fe phases, lower proportion of small-angle grain boundaries and the difference of grain size in different regions leading to the fragile microstructure were the root causes of crack initiation. The higher residual stress of the BM would promote the formation and extension of cracks. The restraining force due to fixture fixation and welding shrinkage force turned the crack to laminar tearing. Preventive measures of laminar tearing were also proposed.