Tensile property and micro-texture evolution of the charge weld in a billet-to-billet extrusion of AA6061 aluminum profile

Abstract

Charge welds occur in profiles during billet-to-billet extrusion of hollow aluminum profiles. To investigate the effects of charge welds on the tensile property of the profile, a tensile test and a fracture scanning test using the scanning electron microscope (SEM) are conducted. The results showed that charge weld plays bad roles in the tensile property of the profile. The tensile samples derived from the charge weld distribution zone are always fractured near the charge welds. In addition, the tensile strengths of the early-stage charge welds are the poorest. To validate the property variations in the charge weld zone along the extrusion directions in a microscale, the evolution of microstructure characteristics and texture in the charge weld distribution zone are discussed with the help of the electron back scattering diffraction (EBSD). The grain morphologies, misorientation, and micro-textures are not uniform along the charge weld in the extrusion direction or on different sides of itself. Incomplete dynamic recrystallization with lower distortion energy and dislocation density due to lack of frictions with dies at the beginning and middle stages of the charge weld results in strip-shaped coarse grains and lower-angle grain boundaries, further revealing the essence of the low tensile strength at the beginning and in the middle of the charge weld. The intensity of shear texture {111} on the charge weld is the largest compared with those on both sides of it, verifying the large plane strain status on the charge weld plane.