Stir zone material flow patterns during friction stir welding of heavy gauge AA5056 workpieces and stability of its mechanical properties

OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 23 No. 4 2021 Mechanical tests of the specimens cut in different directions from the stir zone (scheme in Figure 1) show typical deformation behavior for aluminum-magnesium alloys with an inherent discontinuous ductility effect (Figure 10). Tests of the base metal of workpieces show average ultimate tensile strength values of 301 MPa. Mechanical tests showed that the samples are characterized by suf fi ciently high mechanical properties in the vertical (Figure 10a), transverse (Figure 10b), and longitudinal (Figure 10c) directions compared with the characteristics of the base metal. The average values of the ultimate tensile strength in the vertical, transverse, and longitudinal directions are 302 MPa, 295 MPa, and 303 MPa, the yield strength is 155 MPa, 153 MPa, and 152 MPa, and the relative elongation is 27.2 %, 27.5 %, and 28.7 %, respectively. In addition to suf fi ciently close values of tensile strength, yield strength, and ductility, high stability of deformation behavior under tension can also be noted for the samples, as evidenced by the overlap of the graphs with each other. Evaluation of the tensile strength stability for different loading directions (Figure 11) allows specifying that in general, in the transverse direction, the strength properties are somewhat lower in all measurement areas, but, in all testing directions, the strength of the weld material is higher than the strength of the original sheet metal. In the joint central part, there is also some tendency for the mechanical strength to decrease compared to the values at the top and bottom areas. c Fig. 10. Test diagrams for specimens cut in vertical ( а ), transverse ( b ) and longitudinal ( c ) directions according to the scheme shown in Fig. 1 a b