Materials Science Forum Vol. 969

Abstract: Several case studies have shown that welding of stainless steel to galvanized steel leads to evolution of zinc which can penetrate through the steel and result in cracking, the present study focuses on determination of the effect of zinc on the mechanical behaviour of such weld joints. Welding was carried out using two shielding gas combinations. The other variations in parameters were heat input and presence or absence of zinc coating at the weld location. Tensile tests showed that the ductility of weld specimen improved when the coating was stripped off the samples prior to welding. Impact strength of weld specimens also followed similar trend. The impact strength was found to be improved when welding was done using Ar+2%He+2%O₂ as shielding gas. The compressive strength was found to be similar. To explain the mechanical behaviour of the welded specimen, microstructural characterization of the weld region was carried out.

Abstract: The effect of ZrO₂ (2, 4, 6 and 8 wt%) dispersoids with 1 wt% graphite on the microstructural, mechanical properties on squeeze cast VAL12 matrix hybrid composite is investigated in the present study. The hybrid composites were characterized using advanced characterization techniques to reveal its microstructural and physical properties. The microscopic examinations using optical and SEM technique reveal that the addition of dispersoids accelerates the nucleation kinetics, thus attaining fine, equiaxial grains in hybrid composites. The squeeze cast composites show almost nil porosity, defects and owing to it, the actual density of the composites are found to be more than 95% as that of the theoretical density values. The hardness values and tensile values increase with respect to the increase in percentage addition of ZrO₂. The tensile results show that there is an appreciable increase in the UTS values of composites without much loss in its ductility as the addition of graphite improves the self-lubricating property and provides wettability during the casting. Fractographic studies on tensile tested specimen reveal that the crack occurs in both matrix and particles showing the good interface between matrix and dispersoids. Machinability studies reveal the formation of continuous chips in hybrid composites with a lower percentage of reinforcement (up to 4% ZrO₂ + 1%Gr) and segmented chips in case of the composite with 8% ZrO₂ + 1%Gr, as the increase in the percentage of dispersoids improve the chip breakability of the composites. On an overall, the hybrid aluminium matrix composites with 1%Gr and 6 % ZrO₂ unveiled better optimal results.

Abstract: A finite element model is described in this paper, which investigates the behavior of CFS built-up un-lipped channel sections, connected back to back with the help of intermediate web fasteners, subjected to axial load. Finite element package ABAQUS was used to develop the model for built-up columns, which were validated against the test results reported by the authors recently on another paper. Material non-linearity and initial imperfections were included in the FEA model. A parametric study was conducted using the validated FEA model to investigate the effect of screw spacing on axial strength. Axial strengths obtained from the FEA model were compared against the AISI&AS/NZS design strengths; obtained comparisons showed that the AISI&AS/NZS standards were un-conservative for stub and short columns which failed by local buckling whereas the standards were over-conservative for columns failed through overall buckling.

Abstract: The friction stir welding of polyamide 66 with a specially modified tool is studied. A variation of the conventional friction stir welding is investigated by incorporating a friction plate for the purpose of heating the polymer in the course of welding process through the tool shoulder. This in turn, improves the efficiency of the weld. The association of the welding process parameters and the weld performance has been investigated by the grey relational analysis with multi response characteristics like weld tensile strength, percent elongation and hardness. Macrostructure of the weld joint cross section has been explored by Stereo microscope. The maximum weld tensile strength of 63 MPa and a Shore hardness of 60 D at the weld nugget are obtained. The hardness profiles of the welded samples have been analyzed in this investigation.

Abstract: The microstructure and corrosion properties of weld fusion zone and the heat affected zones of gas tungsten arc (GTA) welded AA2014 alloy, welded at varying speeds of 1.5mm/s, 2.5 mm/s and 3.5 mm/s were examined for gaining knowledge on the effect of welding speed on corrosion behavior at localized regions of the weldment. The macrostructure and microstructure of the welds were evaluated with optical microscope. The corrosion properties were examined with potentiodynamic polarization in aqueous 3.5% NaCl solution. The GTA welding has resulted in grain refinement fusion zone and dispersion of coarse Al₂Cu phases within the grains and along the grain boundaries of heat affected zones. With increase in welding speed the grain size of AA2014 at the fusion zone reduces significantly and also the corrosion resistance of the fusion zone and heat affected zone could decrease as it shows higher negative corrosion potential.

Abstract: Friction stir processing (FSP) is emerging as a singular solid-state surface engineering technique to fabricate surface composites (SC) since its adaption from Friction Stir Welding (FSW) from the early 90s. FSP is a promising technique to overcome the barrier of magnesium being a poor material in terms of wear and corrosion resistant without adding much on the processing cost and thus, widen its applications.The targeted property enhancement by forming surface composites via FSP are strength, ductility, hardness, wear resistance, toughness, fatigue life, formability, corrosion resistance, etc. Although, a decade of research work has been carried out on FSP for different metal alloys, the advantages of the process particularly on magnesium alloys is yet to be understood clearly. The present review is focused on understanding the response of magnesium alloys for friction stir processing to fabricate surface composites. The available literatures have been thoroughly reviewed to present the microstructure evolution during processing and the mechanism of strengthening; the works on magnesium has been summarized to understand the effect of various processing parameters such as tool speed (rotation and traverse), number of passes, etc. and the tool geometry on the resulting properties. Also, details regarding the selection of suitable tool material and reinforcing particles to achieve optimum properties for specific magnesium alloys is included. Important suggestions and scope for further research regarding fabrication of surface composites on magnesium alloy are provided.

Abstract: Hybrid metal matrix composites (HMMC) are advanced materials which are not simply depicting in improvement of mechanical properties but also on characteristics of machinability for thorny shapes to machine. Electric discharge machining (EDM) shows a potential technique for machining hybrid metal matrix composites. An investigation is done on hybrid metal matrix composite for response parameters like MRR, TWR by conducting a range of experiments with choosing typical process parameters such as peak current, tool lift, pulse-on time and pulse-off time.

Abstract: Submerged arc welding (SAW) process is extensively used in major industrial application such as wind turbine towers and ship building industries for joining of larger thickness (~10 to 50mm) of similar and dissimilar materials. However, other joining processes are not popular to weld larger thickness compared to SAW. In welding, one of the major problems is distortion, which destroys the dimensional stability of the component, a major concern in manufacturing. Simulation of larger thickness component will increase the simulation time. Therefore, an attempt has been made to evaluate a 3 - dimensional finite element analysis (FEA) using SYSWELD to study the effect of the joining of two similar shells of High Strength Low Alloy (HSLA) steel through scale down model in the ratio of 10:1. To reduce the simulation time, the two shells of steel having 400mm diameter and 2mm thickness are modelled and simulated with single pass GMAW process using eight different welding sequences as per welding procedure specification (WPS) using SYSWELD. Results show the simulated welding sequence no. 4 has a considerable amount of reduction in distortion of 1.526 mm compared to that of other sequences. Welding sequence no. 4 is then followed by actual windmill tower fabrication, which resulted in reduced distortion level of 5 mm.

Abstract: Finite element method (FEM) is employed to study an effect of diffusion bonding strength between aluminium and its copper material and optimized parameters. The diffusion bonding soundness was estimated at different processing parameters such as temperature, pressure and time. The coefficients of linear thermal expansion (CTE) of the metals induce thermal stress at the bonded area. This phenomenon motivated the study of the stress distribution along with maximum and minimum stress values, while bonding of two dissimilar metals at particular bonding process parameters. The incompatible thermal stress at the bonded area plays a vital role in better bond soundness. Thus, it is required to estimate the bonding interface in dissimilar joints. This study was performed using the FEM and the analysis was carried out using the commercial software package Ansys V12.0

Abstract: The present work focusses on improving the surface wear resistance of commerical pure copper by reinforcing tungsten particles through friction stir processing. Particularly this work adopts Taguchi’s experimental design to achieve minimum wear rate for Copper-Tungsten surface composite by optimizing the process parameters. The rotational and traverse speeds of tool and volume fraction of reinforcement (i.e. tungsten) are the chosen parameters for minimizing the wear rate. Taguchi L9 orthogonal array was used to design the experiments. The surfaces of the processed specimens were investigated by optical microscopy for the distribution of tungsten particles and sliding wear behavior was studied by conducting pin-on-disc method. It was observed from the optical micrographs that the reinforcement evenly dispersed in the processed zone. The measured hardness was 85% higher than the base metal for the specimen exhibited minimum wear rate. The effects of all three parameters on wear rate were studied. The minimum wear rate was achieved by using rotational and traverse speeds of tool, 1200rpm and 60mm/min, respectively. The amount of reinforcement required to achieve maximum wear resistance was 10%. Variance analysis showed that amount of reinforcement played a key role in determining the properties than the other parameters. Keywords: Cu-W composite, high strength high conductivity alloy, friction stir processing, Taguchi optimization