An outlook on comparison of hybrid welds of different root pass and filler pass of FCAW and GMAW with classical welds of similar root pass and filler pass

In the present study, gas metal arc welding and flux cored arc welding were applied on SA516 Gr70 carbon steel material. Two different hybrid passes were applied, wherein flux cored wire and solid wire were applied to root pass and filler pass one by one and vice versa. Besides, two more welds of similar electrode root pass and filler pass of flux cored arc welding and gas metal arc welding were acquired. The comparative analysis was carried out in terms of macrostructure and microstructure examination, tensile testing, hardness variations, and impact testing for these classical welds and hybrid welds. The results reveal that, hybrid welds lead to better impact properties relative to classical welds. Maximum angular distortion of 2.66° was reported with classical weld of gas metal arc welding with solid wire root pass and same filler pass. The maximum impact toughness of 49 J/m³ was reported for flux cored root pass and solid wire filler pass at the weld zone. Maximum tensile strength of 596 MPa was reported for hybrid weld of solid root pass and flux cored filler pass. Microstructures are reported with the presence of different acicular ferrite and grain boundary ferrite. Maximum acicular ferrite of 61% was reported with classical weld of flux cored arc welding.     

Phylogenetic analysis of TCE-dechlorinating consortia enriched on a variety of electron donors

Two rapidly fermented electron donors, lactate and methanol, and two slowly fermented electron donors, propionate and butyrate, were selected for enrichment studies to evaluate the characteristics of anaerobic microbial consortia that reductively dechlorinate TCE to ethene. Each electron donor enrichment subculture demonstrated the ability to dechlorinate TCE to ethene through several serial transfers. Microbial community analyses based upon 16S rDNA, including terminal restriction fragment length polymorphism (T-RFLP) and clone library/sequencing, were performed to assess major changes in microbial community structure associated with electron donors capable of stimulating reductive dechlorination. Results demonstrated that five phylogenic subgroups or genera of bacteria were present in all consortia, including Dehalococcoides sp., low G+C Gram-positives (mostly Clostridium and Eubacterium sp.), Bacteroides sp., Citrobacter sp., and delta Proteobacteria (mostly Desulfovibrio sp.). Phylogenetic association indicates that only minor shifts in the microbial community structure occurred between the four alternate electron donor enrichments and the parent consortium. Inconsistent detection of Dehalococcoides spp. in clone libraries and T-RFLP of enrichment subcultures was resolved using quantitative polymerase chain reaction (Q-PCR). Q-PCR with primers specific to Dehalococcoides 16S rDNA resulted in positive detection of this species in all enrichments. Our results suggest that TCE-dechlorinating consortia can be stably maintained on a variety of electron donors and that quantities of Dehalococcoides cells detected with Dehalococcoides specific 16S rDNA primer/probe sets do not necessarily correlate well with solvent degradation rates.     

Study of Amorphous Compounds Obtained by Ball Milling in the Si–C–O System

Generally, the Si–C–O system is composed of SiO₂, SiC, and pure C as crystalline phases. In the present study, we focus on the preparation of ternary silicon oxycarbide compound. For this purpose, different mixtures of quartz, silicon, and graphite were ball milled to cover the following range of composition: (1) SiC _x O_{2(1 – x)} + excess of C; (2) SiC _x O_{2(1 – x)} stoichiometric; (3) SiC _x O_{2(1 – x)} + excess of Si. The course of the reaction is followed by X-ray diffraction, by measuring the relative intensity change of the Bragg's peaks as a function of the mechanical treatment. The Rietveld method is applied to the patterns for quantitative analysis and determination of crystallite size and microstrain. Finally, the behavior of each phase is reported across the three starting compositions examined here and the presence of silicon oxycarbide compounds induced by ball milling is assessed by [²⁹Si-MAS]NMR.     

Investigation on various welding consumables on properties of carbon steel material in gas metal arc welding under constant voltage mode

In this present work, the influence of different consumables on weld properties of carbon steel plate was studied by automatic gas metal arc welding under constant voltage mode. For all experiments, the process parameters such as welding current of 200 A, voltage of 28 V and welding speed of 200 mm/min were kept constant. The results indicate that the angular distortion remained higher for solid wire, whereas it was minimum for flux-cored wire and the lowest in metal-cored wire. Mechanical properties such as yield strength, tensile strength, elongation and joint efficiency remained high for solid wire relative to cored wire. Excellent impact toughness of the weld metal and heat-affected zone was reported for the flux-cored welds compared with solid wire and metal-cored welds.     

Influence of Friction Stir Processed Parameters on Superplasticity of Al-Zn-Mg-Cu Alloy

Friction stir processing (FSP) is a novel technique for refining the microstructure. In this study, the effect of FSP process parameters such as tool rotation, traverse speed and tool tilt on resulting grain size, microstructure and superplastic behavior of high-strength thick Al-Zn-Mg-Cu alloy is reported. The microstructure examination of the stir zone (SZ) was performed by optical as well as scanning electron microscope. Microstructure variation attributed to different process parameters is reflected in the SZ. It is observed that grain size increases with increasing tool rotation speed, and decreases with increasing traverse speed. However, tool tilt has no significant effect on grain size. Moreover, at higher tool tilt distorted grains were observed in microscopic images. The highest average value of hardness in the SZ is obtained for low heat input value corresponding to higher tool rotation and traverse speed. In this study, hardness has shown no dependency on the grain size of the SZ due to the strengthening of phase particles. Process parameter of 1500 rpm, 31.5 mm/min and 2° tool tilt (low heat input) only exhibited superplastic elongation of 225% at a superplastic condition of 400°C and 3 × 10^?4 s^?1 because of an appropriate material flow without any defect.     

Traveling Wire Electrochemical Discharge Machining (TW-ECDM) of Quartz Using Zinc Coated Brass Wire: Investigations on Material Removal Rate and Kerf Width Characteristics

Silicon - In this era, advanced non-conducting materials are gaining importance due to their superior properties. However, it is difficult to micro-machine these materials inefficiency and also...     

Influence of heat input/multiple passes and post weld heat treatment on strength/electrochemical characteristics of friction stir weld joint

The V-95 and D-19 precipitation hardened Russian aluminum alloys are widely used in the Russian aircraft industry and these alloys are not weldable by conventional fusion weld techniques. This paper intends to evaluate the effect of spindle and weld speed on joint strength characteristics of a single pass (SP) and double pass (DP) friction stir lap weld through a common heat index and to analyze the effect of retrogression and re-ageing treatment (RRA) on joint strength and corrosion characteristics. The strength characteristics were analyzed by welding and shear testing of specimens and corrosion susceptibility of joint through immersion in EXCO solution as per ASTM G34. The trials revealed that the joint strength of the welded alloy is inversely proportional to the heat index and the DP weld provided significantly higher strength than an SP weld. The heat affected zone of the joint was found most sensitized to corrosion. The RRA treatment was found to improve the strength of the joints welded with higher heat input while it slightly degraded the joint strength for low heat input welds. The corrosion characteristics of the welded joint is also significantly improved by the post weld RRA treatment.     

Process parameters/material location affecting hooking in friction stir lap welding: Dissimilar aluminum alloys

Influence of spindle and weld speeds, metal location, direction of spindle rotation, and tool pin length on hooking in lap FSW of dissimilar aluminum alloys and the effect of hook on tensile and fatigue weld strength was studied. Optical images of the cross-section of the specimen welded at different process parameters were analyzed. The results indicate that increased spindle speed, reduced weld speed, higher tool pin length, clockwise spindle rotation, and locating the stronger material at the bottom of the joint increased the size of the hooking defect. Higher weld speeds and very high spindle speeds resulted in lower hook size on the advancing side (AS) compared to the retreating side (RS) of the joint. Welding with low weld speed would result in higher advancing side hook size compared to the retreating side. Friction stir weld joints fabricated with anti-clockwise spindle rotation has been found to have extremely low hook both on the AS and the RS of the joint. The tensile and fatigue strengths of the weld joints and plates are degraded by the hook. The fatigue strength of welded alloys could be improved by a double pass weld, the second pass welded immediately adjacent to the first pass.