Production of AA6061-T6/Al2O3reinforced nanocomposite using friction stir welding

Abstract

Heat-treatable AA6061-T6 weldability leads to a decline in the physio-mechanical and tribological properties due to strengthening precipitates dissolution in the nugget zone of FS-welded joints. Improvement in these properties is governed by reinforcement particles addition in the weld joint line for non-heat treatable Al-alloys. Although, its application to AA6061-T6 is scant. In the present work, FS-welded joints were produced by reinforcing Al2O3 nanoparticles into the faying surface of the base matrix. The purpose of Al2O3 nanoparticles addition is to refine the microstructure of the nugget zone and to obstruct the granular growing in the heat-affected zone. FSW was conducted at constant rotating 2000 rpm, transverse 70mm min-1 speed to illustrate the influence of Al2O3 addition on mechanical, microstructure, micro-hardness, and wear properties of welds compared to parent alloy and unreinforced joints. Findings revealed that Al2O3 nanoparticles addition along the joint line leads to noteworthy grains refinement structure of weld zone (6μm) compared with the base material (38μm) and unreinforced nugget (18μm) joints. In addition, reinforced FS-W nugget zone have banded structure of alternate regions namely, nanoparticles-rich and free those have a difference in grain size, such that, the nanoparticle-rich region has fine grain size (6μm) than nano particle-free (14μm) region. Due to Zener-influence occurred via Al2O3 nanoparticles helps to avoid the grain growth accompanied by dynamic recrystallization throughout FSW process which results in granular size reduction. Tensile strength (246 MPa/73%), microhardness (88HV/52%), and wear properties was notably increased for reinforced FSW joint compared to unreinforced joint (tensile strength (180MPa), micro-hardness (46HV), and lower wear resistance, under similar parameters which attribute to nanoparticles presence in processed area. Moreover, single FSW pass leads to nonuniform distribution of Al2O3 nanoparticles and nucleation of voids at Al/Al2O3 boundary in the heat-affected zone which leads to early fracture of welded joint during tensile loading.