N. Kishore Babu

Influence of current pulsing on microstructure and mechanical properties of Ti–6Al–4V TIG weldments

Abstract The present study has investigated the influence of current pulsing on the structure and mechanical properties of Ti–6Al–4V tungsten inert gas (TIG) weldments. Autogenous full penetration bead on plate TIG welds were made with and without direct current pulsing. Microstructural observations and evaluation of hardness, tensile and fatigue properties of the weldments were made in different conditions: as welded and post-weld heat treatment (PWHT) conditions (PWHT was done at 700 and 900°C). Current pulsing resulted in slight refinement of prior β grains, leading to better tensile strength, ductility and fatigue lives of weldments in the as welded condition. In the case of weldments subjected to PWHTs, the pulsed weldments exhibited inferior fatigue lives compared with the unpulsed weldments. The PWHT done at 900°C resulted in inferior fatigue lives of weldments compared with that done at 700°C.

Grain Refinement of AZ31 Magnesium Alloy Weldments by AC Pulsing Technique

The current study has investigated the influence of alternating current pulsing on the structure and mechanical properties of AZ31 magnesium alloy gas tungsten arc (GTA) weldments. Autogenous full penetration bead-on-plate GTA welds were made under a variety of conditions including variable polarity (VP), variable polarity mixed (VPM), alternating current (AC), and alternating current pulsing (ACPC). AC pulsing resulted in significant refinement of weld metal when compared with the unpulsed conditions. AC pulsing leads to relatively finer and more equiaxed grain structure in GTA welds. In contrast, VP, VPM, and AC welding resulted in predominantly columnar grain structures. The reason for this grain refinement may be attributed to the periodic variations in temperature gradient and solidification rate associated with pulsing as well as weld pool oscillation observed in the ACPC welds. The observed grain refinement was shown to result in an appreciable increase in fusion zone hardness, tensile strength, and ductility.

Effect of titanium-boron additions on grain refinement of AA 2219 gas tungsten arc welds

Abstract Grain refinement of aluminium weld metal involves the transition from coarse columnar grains to smaller, more equiaxed grains (sometimes referred to as columnar to equiaxed transition). This refinement in grain size and shape results in both improved mechanical properties (ductility and toughness) and significant improvement in weldability. The present study has investigated the influence of Tibor additions on the structure and mechanical properties of AA 2219 gas tungsten arc (GTA) weldments. Controlled amounts of Tibor grain refiner (containing Ti and B in a ratio of 5∶1) were introduced into the molten pool of AA 2219 by predeposited cast inserts under different welding conditions by GTA welding. Full penetration GTA welds were prepared using alternating current. It was observed that grain size was decreased with increasing amounts of Tibor. The observed grain refinement was shown to result in an appreciable increase in fusion zone hardness, strength and ductility. It is also found that welds subjected to post-weld aging treatment displayed superior mechanical properties.

Microstructure and Mechanical Properties of Ti-15-3 Alloy Gas Tungsten Arc Welds Prepared Using CP-Titanium Filler

Strength and ductility of fusion zone of metastable β titanium alloy welds can be improved by choosing suitable fillers. This paper reports the effects of using CP-Ti filler on the microstructural and mechanical properties of Ti-15-3 weldments. Full penetration autogenous and CP-Ti filler welds were produced by pulsed gas tungsten arc welding. X-ray diffraction analysis revealed small amounts of α-Ti phase in the diffraction pattern obtained for welds prepared using CP-Ti filler. Transmission electron microscopy analysis showed presence of grain boundary and intragranular α in the fusion zone of the welds prepared using CP-Ti filler. The welds prepared with CP-Ti filler showed higher hardness, higher UTS and lower % strain compared to autogenous welds.

Grain Refinement, Microstructural and Hardness Investigation of C Added Ti-15-3 Alloys Prepared by Argon Arc Melting

Mechanical properties of as-cast beta titanium (β-Ti) alloy can be improved by grain refinement and formation of insoluble precipitate. This paper reports the effect of carbon (C) addition on microstructure and hardness of cast Ti–15V–3Cr–3Sn–3Al (Ti-15-3) samples prepared by argon arc melting. X-ray diffraction analysis of C added as cast Ti-15-3 samples revealed the presence of β-Ti and TiC phases. Scanning electron microscope analysis revealed eutectic TiC precipitates in C added Ti-15-3 samples while a reduction in grain size was observed with increasing carbon addition. Inoculation effect due to TiC and growth restriction by C for β phase resulted in decreased grain size. Hardness of C added Ti-15-3 alloys increased with the increased carbon content of the sample. The improvement in hardness was contributed by grain refinement and the formation of TiC precipitates in the samples.

Improving the corrosion properties of magnesium AZ31 alloy GTA weld metal using microarc oxidation process

In this work, the morphology, phase composition, and corrosion properties of microarc oxidized (MAO) gas tungsten arc (GTA) weldments of AZ31 alloy were investigated. Autogenous gas tungsten arc welds were made as full penetration bead-on-plate welding under the alternating-current mode. A uniform oxide layer was developed on the surface of the specimens with MAO treatment in silicate-based alkaline electrolytes for different oxidation times. The corrosion behavior of the samples was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy. The oxide film improved the corrosion resistance substantially compared to the uncoated specimens. The sample coated for 10 min exhibited better corrosion properties. The corrosion resistance of the coatings was concluded to strongly depend on the morphology, whereas the phase composition and thickness were concluded to only slightly affect the corrosion resistance.

Microstructural and Mechanical Properties Investigation of TiC Reinforced Hardface Alloy Deposited on Mild Steel Substrate

Wear is one of the major problems faced in industry that reduces the life of industrial components and increases the operating costs. Therefore, hardfacing is widely employed by engineers to minimize components’ wear, in which single or multiple layers of hard material that mainly consists of carbides deposited on the base metal. However, these carbide-based materials suffer from solidification cracking due to lack of ductility. In this study, titanium carbide (TiC) reinforced alloy steel deposited using self-shielded flux cored arc welding technique. The microstructure and phase analysis in the hardfaced deposit by scanning electron microscope, energy dispersive x-ray and X-ray diffractometer revealed that the microstructure consists of finely distributed TiC within matrix of martensite and some retained austenite. Microhardness test and pin-on-disk wear test had shown that the clad deposit posses better hardness and wear resistance. Retained austenite formation and TiC precipitation were discussed in detail and correlated with the mechanical properties.

Microstructure Evolution and Mechanical Properties Investigation of Al-6 %Cu Alloy Laser and GTA Welds

Abstract Microstructural development, post-weld ageing response and mechanical properties of gas tungsten arc and CO2 laser welded Al-6 %Cu (AA2219) alloy were investigated in the present study. The fusion zone of laser weld consists of three parts: the fine grains in the middle part, the columnar zone and equiaxed zone adjacent to fusion boundary. In contrast, fusion zone of gas tungsten arc weld consists of two parts: the columnar zone in the middle part and the equiaxed zone adjacent to fusion boundary. The size of the equiaxed grains in the fusion zone was the least in the laser welds when compared to gas tungsten arc welds. Laser welds have exhibited higher hardness, post weld ageing response, yield strength, ductility and fatigue strength when compared with gas tungsten arc welds. Fine equiaxed grain morphology and discontinues eutectic distribution in the laser weld fusion zone could be attributed to the improved tensile and fatigue properties of laser welded samples. ‘Thermal pinning effect’, due to non isothermal conditions, has arrested grain growth in heat affected zone in spite of temperatures close to the melting point of aluminum in heat affected zone.

Enhanced Mechanical Properties of AA5083 GTA Weldments with Current Pulsing and Addition of Scandium

AA5083 alloy is welded with gas tungsten arc welding using optimized welding parameters. Al-Si-Sc master alloy filler with varying contents of scandium is used for welding. Welding was carried out with and without AC-pulsed current techniques. A narrow heat affected zone with more refined grain structure is observed in the case of the pulsed current technique. Furthermore, it is observed that the columnar solidification structure in the fusion zone was suppressed and fine equiaxed grains were formed in the weld zone with increasing scandium content, which is attributed to the grain refinement effect of scandium with the generation of increased nucleating sites during weld solidification. This effect is reflected in mechanical properties also. An increased hardness of about 10 % results with pulsed current technique compared to about 20 % with an addition of 0.75 % scandium. However, in the case of tensile properties pulsing resulted in about 8 % increase in tensile strength and addition of 0.75 % scandium resulted in about 40 % increase in tensile strength. Both the pulsed current technique and the addition of scandium were observed to be better in increasing not only strength but also elongation due to the refined grain structure in the weld fusion zone.

Influence of Welding Speed on Microstructure and Mechanical Properties of AZ31 Magnesium Alloy Laser Weldments

Abstract CO2 laser welds were prepared on 3 mm thick sheets of continuous cast and rolled AZ31 magnesium alloy, using different welding speeds (3 m/min, 4 m/min and 5 m/min). The microstructure and composition analysis of weld metal was examined using optical and scanning electron microscopy (HR-SEM, EPMA and EDS/X). Room temperature hardness and tensile properties of the weldments in the as-welded condition were studied and correlated with the microstructure. The microstructure of fusion zone consists of two parts: the equiaxed zone in the middle part and the columnar zone adjacent to fusion boundary. It has been shown that the average width of columnar grains in the fusion zone is increased with decreasing the welding speed. Microstructural examination showed that the equiaxed grain size in the fusion zone was the least in the welds made using 5 m/min welding speed. It has been shown that welds prepared with 5 m/min welding speed exhibited increase in hardness, yield strength and ductility when compared with other welds.