Structure and properties of friction stir welded joints made in 1565chН2 alloy sheets and plates

Abstract

This paper describes the results of a study that looked at the mechanical properties of friction stir welded butt joints in 3 mm thick sheets and 15 mm thick plates made of aluminium alloy 1565chH2 (Н116). Tensile tests show that the weld tends to fracture in the heat impact zone on the tool retraction side. The tensile strength of the weld is 0.95–0.97 of the tensile strength of the base metal, which is significantly higher than the one achieved in fusion welds. The latter have the strength factor of 0.71–0.73. Together with high strength, the welded joints in 1565chH2 (Н116) alloy sheets and plates have high plasticity. When testing using a punch with the diameter equal to double thickness of the specimen, the bend angle of a sheet joint was found to be 145 degrees and that of a plate joint — 100 degrees, which is 30–68% more than in the case of the base metal. The impact strength of the weld metal is approximately 4 times higher than that of the base metal. The welded joints in 1565chH2 (Н116) alloy sheets and plates have maximum microhardness in the stir zone, whereas the heat impact zone on the tool retraction side, which is where fracture occured during the tensile tests, was found to have low microhardness. The average grain size of the weld was ~6 μm for sheets and ~8.5 μm for plates. The grain size was found to remain the same in the lap area of double-welded plate joints. The fatigue limit at the stress ratio R = –1 based on 107 cycles for welded joints in 1565chH2 (Н116) alloy sheets was 77 MPa, with the fatigue limit of the base metal being 116 MPa. Cyclic load tests showed that the fracture zone in friction stir welded joints made in 1565chH2 (Н116) alloy sheets and plates, starts from the periodic tool marks on the weld face. Fracture analysis of the specimens after the tests indicate that the welds tend to experience ductile fracture in multiple spots. The length of the heat impact zone in friction stir welded joints made in 1565chH2 (Н116) alloy sheets and plates is 3 and 10 mm, correspondingly.