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Metal concentrations (Al, Cr, Ni, Cu, Zn, and Pb), grain size, and total organic carbon content in 29 surface sediment samples from the nearshore area off Calicut were analyzed to determine their distribution and pollution status. Surface sediments were dominantly silts with low percentage of clay and sand at nearshore and offshore areas. The mean metal concentrations were in the following order: Cr > Ni > Zn > Pb > Cu. The enrichment factor and geo-accumulation index of metals suggest that the surface sediments were not polluted by Zn and moderately polluted by Cu and Ni. By contrast, Cr and Pb showed significant enrichment levels. Results from a multivariate statistical analysis suggested that the spatial enrichment of these heavy metals was related to sediment type. Thus, the sediment distribution and their metal enrichment were mainly controlled by local hydrodynamic conditions that caused the winnowing of fine-grained sediments. [ABSTRACT FROM AUTHOR]

Highlights • AISI 316L austenitic stainless steel is successfully joined using the FSW process. • Regression model is developed to predict the tensile strength of the joints. • The regression model is verified for adequacy using statistical tests. • The tensile strength of the joints is correlated to the microstructural features. • Nonlinear optimization method is used for maximizing tensile strength of the joints. Abstract AISI 316L stainless steel sheets were friction stir welded in the butt joint configuration as per the design of experiment (DoE) developed using the response surface method; Box Benkhen design. The primary friction stir welding (FSW) process parameters; tool spindle speed, tool transverse speed, downward force and tool tilt angle were considered as factors of the experiment. A response surface (second order) regression model for the response, ultimate tensile strength (UTS) of the joints as a function of tool spindle speed, tool transverse speed, downward force and tool tilt angle was developed. Statistical tests such as ANOVA, F- ratio and values of actual and adjusted R2 were used to verify the adequacy of the developed model and the model was validated using conformity experimental trials. The analysis of the model showed that the UTS of the joint is sensitive to all the primary FSW parameters. Also, the tool spindle speed, tool traverse speed and downward force have significant interaction effect on the UTS of the joints. The non-linear optimization of the FSW process yielded 604 MPa as optimal UTS corresponding to optimal tool spindle speed of 597 rev/min, tool traverse speed of 74 mm/min, downward force of 13 kN and tool tilt of 1.5°. [ABSTRACT FROM AUTHOR]

In the present research, the influence of friction stir welding (FSW) tool material on the mechanical and microstructural properties of friction stir (FS) welded 316L stainless steel butt joints is investigated. FS welds were produced using two different tungsten based FSW tools having identical tool shoulder and pin profiles. In both the cases, the FSW experimental runs were carried out using tool rotational speed of 600 rpm, welding speed of 45 mm/min, axial force of 11 kN and tool tilt angle of 1.5°. The results of the study show that the joints produced using the tungsten lanthanum oxide tool are having superior mechanical and microstructural properties when compared to the joints produced using tungsten heavy alloy tool. Furthermore, the tool degradation study by mass loss and photographic techniques suggests that the tungsten lanthanum oxide tool is more prone to degradation by plastic deformation, whereas the tungsten heavy alloy tool is more prone to degradation by wear. [ABSTRACT FROM AUTHOR]

• FSW of 316L stainless steel was carried out to study the effect of tool tilt angle. • The change in tool tilt angle altered the material flow characteristics of stir zone. • A highest weld joint strength (96% of the base steel) was achieved. • The best tool tilt angle for FSW of 316L stainless steel was found at 1.5o. The effect of tool tilt angle on mechanical and metallographic characteristics of friction stir welded AISI 316L austenitic stainless steel joints was investigated. Three experimental trials were performed between 0° to 3° in steps of 1.5°, while keeping the other primary FSW parameters constant (tool rotational speed of 600 rpm, welding speed of 45 mm/min and axial load of 11 kN). The experimental findings prove that the tool tilt angle has significant effect on dynamic volume of the stir zone, peak temperature and the intensity of the shear band formation in the weld zone. The weld joint made at 1.5° was the best tool tilt axis that exhibited higher strength and superior microstructural features leading to onion ring formation at the weld stir zone. 0° tilt angle resulted in slight shoulder plunge whereas, 3° tilt angle paved the way to the formation of void in the weld zone. [ABSTRACT FROM AUTHOR]