Showing papers on "Welding published in 2009"

Welding Metallurgy and Weldability of Nickel-Base Alloys

Abstract: Preface. 1. Introduction. 1.1 Ni-base Alloy Classification. 1.2 History of Nickel and Ni-base Alloys. 1.3 Corrosion Resistance. 1.4 Nickel Alloy Production. 2. Alloying Additions, Phase Diagrams, and Phase Stability. 2.1 Introduction. 2.2 General Influence of Alloying Additions. 2.3 Phase Diagrams for Solid-Solution Alloys. 2.4 Phase Diagrams for Precipitation Hardened Alloys--gamma' Formers. 2.5 Phase Diagrams for Precipitation-Hardened Alloys--gamma" Formers. 2.6 Calculated Phase Stability Diagrams. 2.7 PHACOMP Phase Stability Calculations. 3. Solid-Solution Strengthened Ni-base Alloys. 3.1 Standard Alloys and Consumables. 3.2 Physical Metallurgy and Mechanical Properties. 3.3 Welding Metallurgy. 3.4 Mechanical Properties of Weldments. 3.5 Weldability. 3.6 Corrosion Resistance. 3.7 Case Studies. 4. Precipitation Strengthened Ni-base Alloys. 4.1 Standard Alloys and Consumables. 4.2 Physical Metallurgy and Mechanical Properties. 4.3 Welding Metallurgy. 4.4 Mechanical Properties of Weldments. 4.5 Weldability. 5. Oxide Dispersion Strengthened Alloys and Nickel Aluminides. 5.1 Oxide Dispersion Strengthened Alloys. 5.2 Nickel Aluminide Alloys. 6. Repair Welding of Ni-base Alloys. 6.1 Solid-Solution Strengthened Alloys. 6.2 Precipitation Strengthened Alloys. 6.3 Single Crystal Superalloys. 7. Dissimilar Welding. 7.1 Application of Dissimilar Welds. 7.2 Influence of Process Parameters on Fusion Zone Composition. 7.3 Carbon, Low Alloys and Stainless Steels. 7.4 Postweld Heat Treatment Cracking in Stainless Steels Welded with Ni-base Filler Metals. 7.5 Super Austenitic Stainless Steels. 7.6 Dissimilar Welds in Ni-base Alloys - Effect on Corrosion Resistance. 7.7 9%Ni Steels. 7.8 Super Duplex Stainless Steels. 7.9 Case Studies. 8. Weldability Testing. 8.1 Introduction. 8.2 The Varestraint Test. 8.3 Modified Cast Pin Tear Test. 8.4 The Sigmajig Test. 8.5 The Hot Ductility Test. 8.6 The Strain-to-Fracture Test. 8.7 Other Weldability Tests. Appendix A Composition of Wrought and Cast Nickel-Base Alloys. Appendix B Composition of Nickel and Nickel Alloy Consumables. Appendix C Corrosion Acceptance Testing Methods. Appendix D Etching Techniques for Ni-base Alloys and Welds. Author Index. Subject Index.

Effect of welding processes on tensile properties of AA6061 aluminium alloy joints

Abstract: The present investigation is aimed at to study the effect of welding processes such as GTAW, GMAW and FSW on mechanical properties of AA6061 aluminium alloy. The preferred welding processes of these alloys are frequently gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) due to their comparatively easier applicability and better economy. In this alloy, the weld fusion zones typically exhibit coarse columnar grains because of the prevailing thermal conditions during weld metal solidification. This often causes inferior weld mechanical properties and poor resistance to hot cracking. Friction stir welding (FSW) is a solid phase welding technique developed primarily for welding metals and alloys that heretofore had been difficult to weld using more traditional fusion techniques. Rolled plates of 6 mm thickness have been used as the base material for preparing single pass butt welded joints. The filler metal used for joining the plates is AA4043 (Al-5Si (wt%)) grade aluminium alloy. In the present work, tensile properties, micro hardness, microstructure and fracture surface morphology of the GMAW, GTAW and FSW joints have been evaluated, and the results are compared. From this investigation, it is found that FSW joints of AA6061 aluminium alloy showed superior mechanical properties compared with GTAW and GMAW joints, and this is mainly due to the formation of very fine, equiaxed microstructure in the weld zone.

Effect of tool geometry on hook formation and static strength of friction stir spot welded aluminum 5754-O sheets

Abstract: Friction stir spot welding is performed on 5754 Al alloy to investigate the effect of tool geometry on hook formation. Partial metallurgical bond (called as ‘hook’) is formed in the weld region between the overlapped metal sheets. The tool geometry is found to significantly affect the hook formation. First, welds are made to compare the effect of three shoulder profiles: concave, convex and flat (all having threaded cylindrical pins) on the hook geometry and static strength. The inherent concave profile resulted in a higher effective top sheet thickness that produced the highest weld strength. Next, with the concave shoulder profile selected, the effects of two different pin profiles: cylindrical and triangular are evaluated. Under the same process condition, welds made with the cylindrical pin have a continuous hook which bypasses the stir zone and terminates close to the keyhole. By contrast, for welds made with the triangular pin, the hook is directed upwards and then arrested at the periphery of the stir zone. The difference in the hook shape can be attributed to the material flow. Prior study shows that the static strength of welds made with the triangular pin is twice that of welds made with the cylindrical pin.

Ultrasonic Metal Welding of Aluminium Sheets to Carbon Fibre Reinforced Thermoplastic Composites

Abstract: The ultrasonic welding technology is an innovative method to produce hybrid joints for multi-material components. The investigations described in this paper were carried out using the ultrasonic metal welding technique for joining carbon fibre reinforced thermoplastic composites (CFRP) with sheet metals like aluminium alloys or aluminium-plated steels. The achievable mechanical properties as a function of the process parameters are presented. Additionally, microscopic investigations of the bonding zone are discussed. One important advantage of ultrasonic metal welding is the possibility to realise a direct contact between the load bearing fibres of the reinforced composite and the metallic surface without destroying the carbon fibres.

Problems and issues in laser-arc hybrid welding

Abstract: Hybrid welding, using the combination of a laser and an electrical arc, is designed to overcome problems commonly encountered during either laser or arc welding such as cracking, brittle phase formation and porosity. When placed in close contact with each other, the two heat sources interact in such a way as to produce a single high intensity energy source. This synergistic interaction of the two heat sources has been shown to alleviate problems commonly encountered in each individual welding process. Hybrid welding allows increased gap tolerances, as compared to laser welding, while retaining the high weld speed and penetration necessary for the efficient welding of thicker workpieces. A number of simultaneously occurring physical processes have been identified as contributing to these unique properties obtained during hybrid welding. However, the physical understanding of these interactions is still evolving. This review critically analyses the recent advances in the fundamental understa...

The arc characteristics and metal transfer behaviour of cold metal transfer and its use in joining aluminium to zinc-coated steel

Abstract: Cold metal transfer (CMT) is a modified metal inert gas welding process based on short-circuiting the transfer process, characterised by low heat input and no-spatter welding. The arc characteristics and its droplet transfer process have been studied by high-speed video photography. The process was used to join aluminium to zinc-coated steel. The results shows that no-spatter welding and low heat input during the welding process can be realized by CMT, and a dissimilar metal joint with good performance can be obtained by the CMT process.

Arc Plasma Torch Modeling

Abstract: Arc plasma torches are the primary components of various industrial thermal plasma processes involving plasma spraying, metal cutting and welding, thermal plasma CVD, metal melting and remelting, waste treatment, and gas production. They are relatively simple devices whose operation implies intricate thermal, chemical, electrical, and fluid dynamics phenomena. Modeling may be used as a means to better understand the physical processes involved in their operation. This article presents an overview of the main aspects involved in the modeling of DC arc plasma torches: the mathematical models including thermodynamic and chemical nonequilibrium models, turbulent and radiative transport, thermodynamic and transport property calculation, boundary conditions, and arc reattachment models. It focuses on the conventional plasma torches used for plasma spraying that include a hot cathode and a nozzle anode.

Microstructure and mechanical properties of friction stir welded AA6063–B4C metal matrix composites

Abstract: The weldability, microstructure evolution and mechanical properties of an AA6063 aluminium alloy and of two composites with AA6063 matrix reinforced with 6 and 10.5 vol.% B4C during friction stir welding are investigated. A joint efficiency higher than 60% was obtained and increased to over 80% after artificial ageing. The B4C particles size and shape were not affected by the welding process and the particle distribution in the matrix was kept uniform in the weld zone. Evolution of the aluminium grain structure from coarse grains in the base material to the refined, equiaxed grains in the weld centre is described. The microhardness profiles of various B4C concentration materials were measured in both as-weld conditions and after post-weld heat treatments. Other microstructure changes of Al–B4C MMCs after welding and heat treatment are also reported.