Effect Of Friction Stir Processing On The Microstructure And Mechanical Properties In 5083-O Aluminum Alloy

Friction stir processing (FSP) is a new solid-state processing technology, which was developed on the basis of friction stir welding.In this paper, the effect of different FSP conditions on the microstructures and mechanical properties of 5083-O aluminum alloy are studied by means of X-ray analysis, optical microscope, transmission electron microscope, scanning electron microscope and tensile tests. The main results are summarized as following:FSP of 5083-O aluminum alloy was conducted to investigate the effect of processing parameters on the microstructures and mechanical properties. This paper focuses on the research about the influence on the microstructure of 5083-O aluminum alloy and the performance by the FSP technological parameters. The microstructure evolution was investigated at the different FSP joint zones such as stir zone (SZ), thermo-mechanical affected zone (TMAZ) and heat affected zone (HAZ). The base material consisted of large flakes grain structure which was elongated along the rolling direction. SZ shows an asymmetrical'bowl'shape, which has obvious displayed material flow patterns of the "onion ring" shaped plastic flow lines. In the nugget the grain structure is fine recrystallized equiaxed grains. The grain structure of the TMAZ is different from the base material, grains has large deformation and was stretched. The fine structure is attributed to the dynamic recrystallization and severe plastic deformation at the zone of SZ and TMAZ.The FSP processing area was investigated for 5083 aluminum alloy. The well joints are characterized by the SZ, TMAZ and HAZ. The appropriate heat input is the essential condition for attaining good FSP processing area, or leading to the formation of flash defect at the advancing side and the "tunnel" defect inside the processing area.The fine and equiaxed dynamically recrystallized grains were observed in the stir zone. As the diameter of the shoulder and rotation increased, the grain sizes in the stir zone increased. However, with increasing the moving speed, the grain sizes in the stir zone decreased slightly. The mechanical tests show that microhardness of 5083-O alloy has been improved significantly after FSP. At a low moving speed and a 16mm-diameter shoulder, the ultimate tensile strength (UTS) was the lowest. As the diameter of the shoulder decreased and the moving speed increased, the UTS increased and could reach up to 340MPa. The elongation of the stir zone obtained was 122%, higher than that of the base metal. More small grains, Mg atoms and dislocations were observed in the protrusion of arc pattern, resulting in higher hardness in the protrusion. And the fluctuation of the hardness decreased with increasing heat input.