Flow Law, Microstructure and Corrosion Behavior of Friction Stir Welded 5A06 Alloy

The evolution of metal flow, microstructure and corrosion properties of 5A06 alloy after friction stir welding were studied. Results show that the metal on the advancing side is curled directly into the threads and then is extruded down into the weld nugget zone by complex motions of torsion and swirl. However, the material on the retreating side encounters chaotic flow patterns. The electro backscattering diffraction results indicate that the grains in stir zone are pronouncedly refined by dynamic recrystallization, and the average grain size is about 6 mu m. The scanning electron microscope analyses display that beta-phase (Al3Mg2) and Al-6(Mn, Fe) are dispersedly distributed in the stir zone and the Al-6(Mn, Fe) is smaller than that in base material. The hardness profile is characterized by material softening along the cross-section and the minimum hardness (HV) value of 720 MPa is located in the interface between stirring zone and thermo-mechanically affected zone. It is evident that the stir zone exhibits better corrosion resistance than the base material. The corrosion potential of stir zone is 35 mV larger than that in base material (-0.725 V).