Effect of Friction Stir Processing on Microstructure, Mechanical Properties, and Corrosion Fatigue Behavior of AA5083-H111 Metal Inert Gas Welded Joint

Abstract

In this study, friction stir processing (FSP) is applied on MIG welded aluminum alloy 5083-H111 plates, with the objective of improving the mechanical strength and corrosion fatigue life of the welded joints. The process is performed using tool rotational speeds of 500, 750, and 1000 rpm with a constant feed rate of 100 mm/min. The microstructures of the base alloy and the welded samples are studied using an optical microscope. The microhardness, tensile strengths, and corrosion fatigue strength of the welded joints are studied using standard samples and methods. The corrosion fatigue test is investigated in a 3.5% NaCl solution. Microstructural observations reveal large grain refinements after FSP, and the samples processed with the tool rotational speeds of 750 rpm show about 96% reduction in grain size compared to the HAZ region of the MIG welded joint mainly due to the plastic deformation at the nugget zone. The microhardness of the FSPed specimens is improved in comparison with the base metal, although no significant changes in tensile properties are obtained. The results also show that the maximum corrosion fatigue life is achieved for the specimen processed using the rotational speed of 750 rpm. SEM microstructure images of the fracture surface of the sample processed at the rotational speed of 750 rpm show that cracks, probably due to corrosion fatigue, initiate from the weld toe and propagate to the cross section of the sample.