Tensile and fracture behavior in 6061-T6 and 6061-T4 aluminum alloys welded by pulsed metal transfer GMAW

摘要

In this investigation, mechanical properties, failure mechanism, and microstructural features of 6061-T6 and 6061-T4 aluminum alloy plates welded by gas metal arc welding in pulsed metal transfer mode are analyzed. Samples were submitted to a standard heat pretreatment of solubilization at 350 degrees C (T4) which revealed the presence of beta('')-phase (Al, Mg, Si) precipitates dissolved in the aluminum matrix. The size of precipitates grew up from 3.58 to 4.12 mu m after the solubilization, while the volumetric fraction increased from 2.35 to 2.97% and Rockwell hardness decreased from 82 HR15T to 61 HR15T as a consequence of the pretreatment process. After welding, the best mechanical properties in tensile strength were found in 6061-T4 samples, reaching 117.48 MPa, in contrast to the 6061-T6 sample processed with similar conditions which reached 73.57 MPa. X-ray energy dispersive spectroscopy revealed the presence of Mg and Cu, which are precursors of the formation of the hardening beta('')-phase, which dissolves in the diffusion zone leading in lower hardness regions due to the diminishing of precipitates and the increase in the grain size; this phenomenon causes a ductile failure mechanism. The best parameters in this study were identified for the sample welded with a current of 250 A, a heat flux of 1.084 KJ/mm and 294 mm/min as feed rate.