Experimental studies on friction-stir welding of AA6061 using Inconel 601 tool

Abstract

Nickel-based superalloy Inconel 601 has been used as tool material during friction-stir butt welding of AA6061-T6 plates. The unique properties of Inconel 601 viz. excellent high-temperature strength, strong work-hardening tendency, and high resistance to wear have been reported beneficial to utilize the material for potential use of FSW tool. Welding has been carried out in different combinations of tool rotation and traverse speed; joint performance in terms of ultimate tensile strength and micro-hardness has been studied. Optical microscopy has revealed existence of fine equiaxed gains at the nugget zone promoting relatively more refined grain structure as compared to the parent material. In few specimens, welding induced defects such as weld flash, kissing bond, zigzag line and tunnel defects have been identified. Maximum tensile strength ~ 133 MPa has been obtained at tool rotational speed ~ 1120 RPM and traverse speed ~ 40 mm/min. Fractographic analysis has revealed two distinct types of fracture mode in the specimens which have failed before the joint and at the joint, respectively. The specimens, failed before the weld zone, have corresponded to ductile fracture mode indicating dimples and ripples. On the contrary, beach marks (wavy patterns) have been noticed in the fractographic analysis of specimens which failed at the weld zone. After completing all welding experiments, the tool has been found not affected by wear, profile distortion by plastic deformation. Hence, application of the said tool can be advised provided the cost of machining the tool with desired pin profile is compromised.