Effects of tool shoulder geometry on mechanical properties and microstructure of friction-stir welded joints of AA5083-0 aluminium alloys

Shoulder geometry is an important geometrical feature of tool design in friction stir welding since it has a strong effect on heat generation and material flow. In this paper the effect of shoulder geometry of tool on mechanical properties, microstructure evolution, and thermal history of friction stir welded joints of AA5083-O aluminium alloy. Two different shoulder geometries of tool named concave and featured (concentric circles) were used, both with cylindrical threaded pin. A set of samples were fabricated using a milling machine and a factorial experimental design to estimate the effects of process parameters (rotational and welding speed) and shoulder geometry on welded joints. Tensile strength, hardness, and microstructure evolution were experimentally measured. These observations were complemented with results obtained from a finite element modelling to calculate thermal history in welded joints. The results showed that the combination of revolution pitch R-value and shoulder geometry of tool were the most significant factors, affecting to mechanical properties, thermal behaviour, and microstructure evolution. The best tensile properties were obtained with a featured shoulder tool using 1400 rpm and 16 mm.min-1, and 1085 rpm and 11 mm.min-1 for rotational and welding speed. The same parameter combination resulted in a joint efficiency of 70% and 65%, respectively. In addition, the results of evaluation using an ANOVA analysis with fixed factors showed that increasing R-values produces statistically significant differences in ultimate strength (Sut) values.

Effects of Shoulder Geometry on Microstructures and Mechanical Properties of Probeless Friction Stir Spot Welded Aluminum 7075-T651 Sheets

In this work, three types of probeless tools (archimedes, involute, and concave tools) were designed. A 7075-T651 sheet of 1.0 mm thickness was welded using the designed probeless tools. It was found that the stir zone and hook defect varied a lot for different joints. Plunge depth was the dominant process parameter for joint property. The joint’s maximum failure load (5.73 kN) was obtained with the concave tool when the target plunge depth was 0.55 mm. Two typical joint fracture modes (shear fracture and plug fracture) were found using three designed tools with different plunge depths, rotation speeds, and dwell times. Shoulder geometry presented little influence on heat generation. Compared with involute grooves, archimedes grooves showed to be more effective on the material flow. The properties of the joints with the archimedes tool were more sensitive to welding parameters. Compared with the flat tool, the concave tool decreased the escape of plasticized material, improved the forge force, and optimized the metallurgical bond at the interface.

Optimization of the Specimen Geometry of Unidirectional Reinforced Composites with a Fibre Orientation of 90° for Tensile, Quasi-Static and Fatigue Tests

When testing unidirectional reinforced composites with a fiber orientation of 90° in tensile tests with rectangular specimens, the influence of the clamping often causes a failure in their vicinity and therefore the test cannot be regarded as valid. In this paper, a test specimen design was determined which is well suited for testing the material properties transverse to the fiber direction by calculating the influence of geometric details of shoulder bar specimens with the help of finite element simulation. The particularly critical clamping and shoulder areas were examined more closely to ensure failure mainly in the test field. In the clamping area the design of the glued-on tabs was investigated and in the shoulder area an optimization of the shoulder geometry was done. Based on the two optimized design proposals, test specimens were produced and evaluated by monotonous tensile tests. Subsequently, Wöhler tests were carried out at different R-ratios and load levels and compared with results of rectangular specimens.

Effects of shoulder geometry of tool on microstructure and mechanical properties of friction stir welded joints of AA1100 aluminum alloy

En este trabajo se estudiaron los efectos de la geometría del hombro de la herramienta en la evolución de la microestructura y las propiedades mecánicas de juntas soldadas de aleación de aluminio AA1100 obtenidos por fricción-agitación usando una máquina fresadora. Tres diseños de hombros se evaluaron con el objetivo de inducir distribuciones diferentes de ciclos térmicos en las regiones de soldadura. Los ciclos térmicos se midieron utilizando termopares y un sistema de adquisición de datos. Caracterización microestructural y análisis cristalográfico de las regiones soldadas se hicieron usando, microscopía óptica y electrónica de barrido, además de difracción de electrones retrodispersados. Las propiedades mecánicas se determinaron por ensayos de tracción, doblez guiado y pruebas de dureza. El comportamiento de la soldabilidad se estableció con base en datos experimentales. Los resultados mostraron que las herramientas con hombro configurado tienen un efecto importante en los ciclos térmicos, generando una amplia región plastificada y el mayor tamaño de grano en la zona de agitación en comparación con la herramienta de hombro plano.

Optimization of Tensile Properties Based on Spin Tool Shoulder Geometry for Friction Stir Welded 6061 Aluminum Alloy

This study reported the statistical optimization based on Taguchi designed experiments to improve the tensile properties of 6061 Aluminum alloy by the friction stir welding (FSW) experiments. The morphology and the structure of the friction stir welded experiments were characterized by scanning electron microscopy. Based on analysis of variance, the impacts of control factors have been identified for the tensile strength of 6061 aluminum alloy by friction stir welding. Experimental results revealed that the defect free butt joints could be obtained by cylindrical-screw type of tool shoulder and the joints made with a cylindrical-screw type resulted in better tensile properties compared to the other two shoulder geometries. Furthermore, it was clear that the tensile properties are greatly improved by friction stir welded experiments in the Taguchi design, and these findings have achieved the desired values in regard to the friction stir welded Experiments. The proposed procedure was applied at friction stir welded experiments, and the implementation results demonstrated its feasibility and effectiveness to enhance the tensile properties by FSW .