G. Madhusudhan Reddy

Microstructural refinement of weld fusion zones in α-β titanium alloys using pulsed current welding

Abstract Pulsing of the welding current is one approach for refining the fusion zone grain structure in α – β titanium alloy welds. This paper reports work in which gas tungsten-arc welds were produced in two α – β titanium alloys under a variety of conditions including direct current (d.c.) pulsing and alternating current (a.c.) pulsing. The results show that, while d.c. pulsing did also refine the weld metal β grain structure, the effect of a.c. pulsing was much greater. Current pulsing enhances fluid flow, reduces temperature gradients and causes a continual change in the weld pool size and shape. These effects, which are believed to be responsible for refining the solidification structure, are much stronger in a.c. pulsing than in d.c. pulsing. The observed grain refinement was shown to result in an appreciable increase in fusion zone tensile ductility. Post-weld heat treatment improved ductility both in pulsed and unpulsed welds, but pulsed welds showed greater tensile elongation even in the heat treated condition.

Weld microstructure refinement in a 1441 grade aluminium-lithium alloy

Clad 2 mm thick sheets of Russian 1441 grade Al-Li alloys were welded using a gas tungsten arc welding process (GTAW). Comparisons were made between the weld beads obtained under (i) continuous current (CC), (ii) pulsed current (PC), and (iii) arc oscillation (AO) conditions for their macro- and microstructural details. In the case of CC GTAW, sound welds could be produced only under a narrow range of welding parameters. Centre line cracks, which occurred in CC GTAW welds under certain conditions, were halted by switching to PC or AO conditions while the welding was in progress. Microstructural refinement was significant in the case of PC and AO GTA welding.

Control of Laves phase in Inconel 718 GTA welds with current pulsing

AbstractThe presence of Nb rich Laves phase in Inconel 718 weld fusion zones is known to be detrimental to weld mechanical properties. In the present study, an attempt was made to control the formation of Laves phase in alloy 718 gas tungsten arc welds using pulsed current. Welds were produced in 2 mm thick sheets of the alloy with constant current and pulsed current and were subjected to post-weld solution treatment at 980°C followed by aging. Detailed microstructural studies and tensile tests at 650°C were conducted. The results show that the use of current pulsing (i) refines the fusion zone microstructure, (ii) reduces the amount of Laves phase and exerts a favourable influence on its morphology and (iii) improves the response of the fusion zone to post-weld heat treatment and weld tensile properties.Abstract The presence of Nb rich Laves phase in Inconel 718 weld fusion zones is known to be detrimental to weld mechanical properties. In the present study, an attempt was made to control the formation of Laves phase in alloy 718 gas tungsten arc welds using pulsed current. Welds were produced in 2 mm thick sheets of the alloy with constant current and pulsed current and were subjected to post-weld solution treatment at 980°C followed by aging. Detailed microstructural studies and tensile tests at 650°C were conducted. The results show that the use of current pulsing (i) refines the fusion zone microstructure, (ii) reduces the amount of Laves phase and exerts a favourable influence on its morphology and (iii) improves the response of the fusion zone to post-weld heat treatment and weld tensile properties.

A comparative evaluation of gas tungsten and shielded metal arc welds of a “ferritic” stainless steel

Abstract The effect of welding process shielding gas and the addition of grain refining elements on the weld zone tensile properties of a ferritic stainless steel conforming to AISI 430 has been investigated. Gas tungsten arc welds exhibiting equi-axed grain morphology had superior tensile and yield strength compared to shielded metal arc welds. The tensile ductility of gas tungsten arc welds was also on an average marginally greater than that of shielded metal arc welds. Welds in general showed low ductility compared to that of the base metal. The addition of titanium and copper led to improved strength over that of the base alloy. The observed properties could be correlated to the austenite content and the fracture morphology.

Microstructure and Mechanical Properties of Friction Stir Lap Welded Aluminum Alloy AA2014

F riction stir lap welds were produced in 3 mm thick Alclad sheets of Al alloy 2014-T4 using two difierent tools (with triangular and threaded taper cylindrical pins). The efiects of tool geometry on weld microstructure, lap-shear performance and failure mode were investigated. The pin proflle was found to signiflcantly in∞uence the hook geometry, which in turn strongly in∞uenced the joint strength and the failure mode. Welds produced in alloy 2014-T4 Alclad sheets by using triangular and threaded taper cylindrical tools exhibited an average lap-shear failure load of 16.5 and 19.5 kN, respectively, while the average failure load for standard riveted joints was only 3.4 kN. Welds produced in alloy 2014-T6 Alclad sheets and in alloy 2014-T4 bare sheets (i:e:, no Alclad) were comparatively evaluated with those produced in alloy 2014-T4 Alclad sheets. While the welds made (with threaded taper cylindrical tool) in T6 and T4 conditions showed very similar lap-shear failure loads, the joint e‐ciency of the welds made in T6 condition (43%) was considerably lower (because of the higher base material strength) than those made in T4 condition (51%). The Alclad layers were found to present no special problems in friction stir lap welding. Welds made with triangular tool in alloy 2014-T4 Alclad and bare sheets showed very similar lap-shear failure loads. The present work provides some useful insights into the use of friction stir welding for joining Al alloys in lap conflguration.

Microstructure and mechanical properties of Inconel 718 electron beam welds

Abstract Bead on plate, full penetration electron beam welds were produced in 2 mm thickness sheets of Inconel 718 in the solution treated condition. Welds were subjected to an aging treatment with and without post-weld solution treatment. Weld microstructures, high temperature tensile properties and stress rupture properties were evaluated. The as welded fusion zone showed a considerable amount of interdendritic niobium segregation and brittle intermetallic Laves phase. The tensile and stress rupture properties of the welds after post-weld aging treatment were found to be inferior in relation to the base metal. Post-weld solution treatment at 980°C was found to result in partial dissolution of Laves phase, some reduction in niobium segregation and the formation of δ phase needles around the Laves particles. The use of 980°C solution treatment was found to improve the weld properties to some extent, although not to the level of the base metal. The reasons for this behaviour are discussed, correlating microstructures, fracture features and mechanical properties.

Friction surfacing : novel technique for metal matrix composite coating on aluminium-silicon alloy

Abstract The present work pertains to the study of wear and corrosion resistance of surface coating of SiCp reinforced AA 2124 aluminium alloy composite onto the surface of aluminium alloy A356. In order to improve wear and corrosion resistance of A356 Al–Si alloy, SiCp reinforced composite was coated on A356 Al–Si alloy substrate by friction surfacing technique. The coating was characterised by metallography, dry sliding wear and potentiodynamic polarisation testing. The present study revealed that aluminium alloys could be friction surfaced with metal matrix composites. The coating exhibited excellent wear resistance, which is attributed to the formation of strong metallurgical bond with the substrate. The coating was also found to have adequate corrosion resistance. The study assumes special significance as deposition of metal matrix composites utilising friction surfacing is reported for the first time.

Effect of Welding Processes and Consumables on Tensile and Impact Properties of High Strength Quenched and Tempered Steel Joints

Quenched and tempered steels are prone to hydrogen induced cracking in the heat affected zone after welding. The use of austenitic stainless steel consumables to weld the above steel was the only available remedy because of higher solubility for hydrogen in austenitic phase. In this investigation, an attempt was made to determine a suitable consumable to replace expensive austenitic consumables. Two different consumables, namely, austenitic stainless steel and low hydrogen ferritic steel, were used to fabricate the joints by shielded metal arc welding (SMAW) and flux cored arc welding (FCAW) processes. The joints fabricated by using low hydrogen ferritic steel consumables showed superior transverse tensile properties, whereas joints fabricated by using austenitic stainless steel consumables exhibited better impact toughness, irrespective of the welding process used. The SMAW joints exhibited superior mechanical and impact properties, irrespective of the consumables used, than their FCAW counterparts.

Effect of welding process on the ballistic performance of high-strength low-alloy steel weldments

The resistance against projectile penetration of the various zones in the weldments of a high-strength low-alloy steel has been studied. A comparison has been made between weldments obtained through three welding processes, namely: shielded metal arc welding (SMAW); gas tungsten arc welding (GTAW); and flux cored arc welding (FCAW). In all of the weldments, the projectile passed through all of the weld zones. However, the ballistic limit has been found to be highest in the case of the SMAW weld and least in respect of FCAW welds. The heat-affected zone (HAZ) of SMAW was resistant to penetration and exhibited the highest ballistic limit, whilst the HAZ of FCAW exhibited an intermediate performance. The ballistic performance of the weldments has been explained on the basis of the weld-zone microstructure, the hardness gradients across the weldments and the thermal efficiencies of the three welding processes.

Ballistic performance of high-strengh low-alloy steel weldments

Abstract Heat-affected-zone (HAZ) softening in a quenched and tempered steel has been studied. The effect of heat-input on the width of the soft zone and, in turn, its influence on hardness and ballistic performance has been investigated. It is observed that increased heat-input results in a wide soft zone, leading to poor ballistic performance: this has been attributed to softer microstructural constitutents. An empirical relationship between the width of the soft zone and the projectile diameter has been proposed to serve as a guide for the analysis of ballistic performance.