INFLUENCE OF TOOL SHAPE FOR FRICTION STIR WELDING ON PHYSICOMECHANICAL PROPERTIES OF ZONES OF WELDS OF ALUMINIUM ALLOY EN AW 6082-T6

摘要

The paper presents the results of studying the formation of macrostructure and distribution of mechanical properties in welded joints of flat specimens from aluminium alloy EN AW 6082-T6 of 8 mm thick, produced by the method of friction stir welding with application of three types of specially designed pins with collars: C-cylindrical threaded pin and collar with a spiral groove; T-cylindrical threaded pin with three grooves and collar with a spiral groove; S-smooth cylindrical pin without thread and flat collar. Friction stir welding was performed in the equipment of the Institute of Welding in Gliwice (Poland), and treatment and mechanical tests were conducted at the E.O. Paton Electric Welding Institute of the NAS of Ukraine. Mechanical testing by indentation was performed in Micron-gamma device, which allows experimental identification of structural state of metal after refinement and determination of the strain hardening presence by limiting values of ratio of hardness to Young's modulus of elasticity. It was found that for all three specimens the HAZ hardness decreases, and in the zone of thermomechanical effect the hardness increases. Maximum hardness values are inherent to the central part of welded joint nugget, as well as to light-coloured oval concentrated fragments of structure in the nugget upper and lower part. Judging by the presence of nanosized hardened structure and uniformity of its distribution in the nugget, as well as good dispersion of oxide films and absence of discontinuities, the friction stir welding with C-type tool can be regarded as the optimum variant. An assumption was made that formation of a uniform structure in welds can be achieved at three-four rotations of the tool in friction stir welding in one place.