E XPERIMENTAL AND NUMERICAL STUDY OF 6061-T6 AL- ALLOY FATIGUE LIFE USING FRICTION STIR WELDING

Abstract

Welded parts are often subjected to variable loads. Paper’s aim is to evaluate the fatigue
characteristics of friction stir welding of AA6061-T6 alloy under variable loading and
observed the influence of heat treatment for friction stir welding joint on the fatigue stress
analysis. The microstructure of the welds alloy are studied before and after heat treatment.
The friction stir welding was employed using milling machine with constant tool rotation
(1000 rpm) and feed rate (20 mm/min). Artificial aging are made for aluminum friction stir
welded alloy using electrical furnace at temperature of 500ºC for 20 min. Quenching at
190ºC for 4 hr. via water is followed the aging process. Fatigue test were done for specimens
(base metal, friction stir welding alloys before and after heat treatment) to obtain the S-N
curves for each case. Finite element via ANSYS software is used to analysis the FSW
(temperature, Von-Mises stress, deformation in the welded zone and contact friction stress
distributions) and Fatigue test (fatigue life, fatigue damage, fatigue safety factor, biaxiality
indication , equivalent alternating stress and stress intensity factors) where the general
thermo-elasto plastic relation produced under thermal and mechanical loads with isotropic,
kinematic and mixed hardening rule in three dimensional problems is proposed. The results
shown that the heat treatment for the friction stir welded alloy would be increased the
fatigue strength of the welded plate that the number of cycles of base metal (AA6061-T6)
was 1.2×106 and the number of cycle for welded joints without heat treatment was
(0.9×106), where the number of cycles was 1×107 with heat treatment with quenching within
4hr. also it can be concluded that, the fracture opening mode (mode I) is exist in the un
heated welded alloy and disappeared with heating treatment