Microstructural evolution and mechanical properties of friction-stir-welded Al–Mg–Si joint

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 595; pp. 196 - 204
• Main Authors: Morita, Tatsuro, Yamanaka, Mikio
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 10-02-2014; Elsevier
• Subjects: Aluminum alloy; Applied sciences; Cold working, work hardening; annealing, quenching, tempering, recovery, and recrystallization; textures; Cross-disciplinary physics: materials science; rheology; Crystallographic texture; Exact sciences and technology; Fatigue; Fatigue strength; Friction-stir welding; Hardness distribution; Joining, thermal cutting: metallurgical aspects; Materials science; Mechanical properties; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Other heat and thermomechanical treatments; Physics; Treatment of materials and its effects on microstructure and properties; Welding; Mechanical properties; Hardness distribution; Friction-stir welding; Crystallographic texture; Fatigue strength; Aluminum alloy; Cubic lattices; Fracture; Mechanical joint; High temperature; Immersion; Precipitation hardening; Texture; Corrosive environment; Ageing; Rupture; Dynamical recrystallization; Hardness; Preferred orientation; Tensile strength; Fatigue crack; Friction stir welding; Extrusion; Heat affected zone; Microstructure
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2013.11.074

This study was conducted to investigate joint and mechanical properties and fatigue strength of a friction-stir-welded aluminum alloy (FSW material), using a platy extruded shape of JIS A6N01S-T5 alloy as a substrate. Furthermore, changes in mechanical properties of FSW material in a corrosive environment were examined. The substrate possessed a typical cubic crystallographic texture in a platy extruded shape of aluminum alloy. Approaching the stir zone from the substrate side, the texture greatly changed and a pair of symmetrical preferred orientations was formed. In the stir zone, the texture gradually changed along the outside of the probe of a rotating tool. FSW refined the microstructure in the stir zone through dynamic recrystallization. In the heat-affected zone (HAZ), reduction in hardness was marked because no refinement of the microstructure occurred and also heat input by FSW weakened precipitation hardening. As a result, tensile fracture of the FSW material occurred along the HAZ; however, tensile strength was maintained at 81% of the substrate. Even after immersion for a long term in salt water kept at a relatively high temperature, no harmful influence of FSW on mechanical properties was found, and rather tensile strength recovered to the level of the substrate by re-aging during immersion. Moreover, although fatigue cracks were initiated from the root of burrs formed by FSW, fatigue strength was maintained at 88% of the substrate.