X-ray Diffraction Study of Static Tensile Deformation in 1050 Aluminum Weld Metal

Abstract

Static tensile test was performed on base metal and weld metal of 1050 aluminum sheets, and investigation was made on the relationship between mechanical properties and solidification mode. Elongation of the weld metal was much less than that of the base metal, and decreased gradually as welding speed increased. This phenomenon was due to the growth mode of columnar crystals. Tensile strength, however, had almost the same value. Tensile cracks initiated mainly along grain boundaries of columnar crystals which were nearly normal to the tensile direction.
The change of lattice strain and coherent domain size during tensile deformation was obtained by X-ray diffractometry. The lattice strain increased as nominal tensile strain increased, and the lattice strain in the weld metal had larger values than in the base metal. Initially the coherent domain size decreased abruptly and after that decreased gradually as the nominal tensile strain increased. In the weld metal the coherent domain size was less than in the base metal.
Besides, the change of features of dislocations during the tensile deformation was observed with transmission electron microscope. The dislocations were multiplicated as the nominal tensile strain increased, and dislocation cell structure was developed. The dislocation cell structure was developed more easily in the weld metal than in the base metal. In the weld metal many discloations were observed near subboundaries which had been developed during solidification. When the tensile strain was 2.5% the size of the dislocation cell structure in the weld metal was about 2.5μ. This size decreased to about lμ when the tensile strain was 13%. The sizes in the base metal were larger than in the weld metal. The changes of the lattice strain and the coherent domain size were due to the change of the features of dislocations during the tensile deformation.