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Srinivasa Rao, K.
- Studies on Partially Melted Zone and Pitting Corrosion Resistance of A356 Aluminium-Silicon Alloy GTA Welds
Abstract Views :333 |
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Authors
Affiliations
1 Department of Metallurgical Engineering, Government Polytechnic, Visakhapatnam-530 007, IN
2 Metal Joining Group, Defence Metallurgical Research Laboratory, Hyderabad-500 058, IN
3 Department of Metallurgical Engineering, Andhra University College of Engineering(A), Visakhapatnam-530 003, IN
1 Department of Metallurgical Engineering, Government Polytechnic, Visakhapatnam-530 007, IN
2 Metal Joining Group, Defence Metallurgical Research Laboratory, Hyderabad-500 058, IN
3 Department of Metallurgical Engineering, Andhra University College of Engineering(A), Visakhapatnam-530 003, IN
Source
Indian Welding Journal, Vol 47, No 1 (2014), Pagination: 27-42Abstract
Gas Tungsten Arc Welding (GTAW) of Pressure Die cast A356 Al-Si alloy with strontium modification was done both with and without filler. The microstructural changes in Weld metal zone (WM), Heat affected zone (HAZ) and Partially Melted Zone (PMZ) were studied. PMZ of aluminium alloy weld is an important region, as it is the weak link in the weldments. It is significantly affected by the welding parameters, filler metal and prior thermal condition. In the present work affect of welding techniques i.e. Continuous Current Gas Tungsten Arc Welding (CCGTAW) and pulsed Current Gas Tungsten Arc Welding (PCGTAW) on microstructure and pitting corrosion resistance of weld metal, Partially melted zone and Heat affected zone in the prior conditions of as cast and T6 conditions were studied. Susceptibility to liquation was found to be less in the weld made in as cast condition of pulsed current GTA welds compared to that of artificially aged condition (T6) of continuous current GTA welds. This was mainly attributed to the silicon enrichment of eutectics at the grain boundaries. Potentiodynamic polarization testing was carried out to study the pitting corrosion behavior of the welds. Pitting corrosion resistance of weld made with pulsed current GTAW of as cast alloy is better than the that of weld made with continuous current GTAW of T6 alloy. This is mainly attributed to the discontinuous eutectic formation at the grain boundary base metal and PMZ.Keywords
Aluminium Alloys, GTA Welds, Partially Melted Zone, Continuous Current Gas Tungsten Arc Welding, Pulsed Current Gas Tungsten Arc Welding.
- Effect of Welding Process on Microstructure and Pitting Corrosion Behavior of AA2014 Al-Cu Alloy Welds
Abstract Views :377 |
PDF Views:4
Authors
Affiliations
1 Department of Mechanical Engineering, GITAM Institute of Technology, GITAM University, Visakhapatnam - 530045, IN
2 Department of Metallurgical Engineering, Government Polytechnic, Visakhapatnam - 530 007, IN
3 Metal Joining Group, Defence Metallurgical Research Laboratory, Hyderabad - 500 058, IN
4 Department of Metallurgical Engineering, Andhra University College of Engineering (A), Visakhapatnam- 530 003, IN
1 Department of Mechanical Engineering, GITAM Institute of Technology, GITAM University, Visakhapatnam - 530045, IN
2 Department of Metallurgical Engineering, Government Polytechnic, Visakhapatnam - 530 007, IN
3 Metal Joining Group, Defence Metallurgical Research Laboratory, Hyderabad - 500 058, IN
4 Department of Metallurgical Engineering, Andhra University College of Engineering (A), Visakhapatnam- 530 003, IN
Source
Indian Welding Journal, Vol 45, No 3 (2012), Pagination: 29-40Abstract
Wrought AA 2014 Al-Cu alloy in mill annealed (O) condition and naturally aged (T4) condition was welded by the Gas Tungsten Arc Welding (GTAW) and Friction Stir Welding (FSW) processes. The microstructural changes and pitting corrosion behaviour in all zones of welds for both the welding processes have been investigated when the alloy was welded in O as well as in T4 conditions. It was observed that naturally aged (T4) alloy weld exhibited better corrosion properties than annealed (O) alloy weld this is attributed to the precipitation of fine grained eutectics in T4 alloy during welding. The pitting corrosion resistance was found to be better and uniform through out cross section of the friction stir welds compared to GTA welds, indicating improvement in corrosion properties of the welds in solid state welding.Keywords
Gas Tungsten Arc Welding, Friction Stir Welding, AA2014 Alloy, Partially Melted Zone, Thermomechanically Affected Zone, Pitting Corrosion, Potentiodynamic Polarization.- Corrosion Resistance of Friction Stir Welded AA6061 Aluminium Alloy
Abstract Views :350 |
PDF Views:4
Authors
Affiliations
1 Department of Metallurgical Engineering, Government Polytechnic, Visakhapatnam, IN
2 Defence Metallurgical Research Laboratory, Hyderabad, IN
3 Department of Metallurgical Engineering, Andhra University College of Engineering (A), Visakhapatnam-530 003, IN
1 Department of Metallurgical Engineering, Government Polytechnic, Visakhapatnam, IN
2 Defence Metallurgical Research Laboratory, Hyderabad, IN
3 Department of Metallurgical Engineering, Andhra University College of Engineering (A), Visakhapatnam-530 003, IN
Source
Indian Welding Journal, Vol 45, No 3 (2012), Pagination: 41-53Abstract
Present work pertains to microstructure and the corrosion behaviour of the nugget zone (NZ), thermo mechanically affected zone (TMAZ) and heat affected zone (HAZ) of friction stir welded AA6061 alloy. An attempt was made to find the influence of prior thermal temper of the alloy. Potentio-dynamic polarisation testing was used to determine the pitting corrosion resistance of the welds. Optical microscopy (OM) and transmission electron microscopy (TEM) with Energy dispersive X-ray spectroscopy studies were carried out to find the mechanism of formation of TMAZ and corrosion. Friction stir welding of this alloy resulted in fine recrystallized grains in weld nugget which has been attributed to frictional heating and plastic flow. The process also produced a softened region in the weld nugget, which may be due to the dissolution and growth of possible precipitates. Corrosion resistance of nugget zone has been found to be higher than that of TMAZ and base metal. Corrosion resistance of naturally aged (T4) alloy exhibit higher corrosion resistance than that of artificial aged (T6) alloy.Keywords
Pitting Corrosion, General Corrosion, Dynamic Polarisation, Friction Stir Welding, Aluminium Alloys.- Microstructure, Mechanical and Corrosion Behaviour of AA7075 Aluminium Alloy Friction Stir Welds
Abstract Views :404 |
PDF Views:17
Authors
P. Vijaya Kumar
1,
G. Madhusudhan Reddy
2,
G. Madhusudhan Reddy
2,
K. Srinivasa Rao
3,
K. Srinivasa Rao
3
Affiliations
1 Department of Mechanical Engineering, Raghu Institute of Technology, Visakhapatnam, IN
2 Defence Metallurgical Research Laboratory, Hyderabad, IN
3 Department of Metallurgical Engineering, Andhra University, Visakhapatnam, IN
1 Department of Mechanical Engineering, Raghu Institute of Technology, Visakhapatnam, IN
2 Defence Metallurgical Research Laboratory, Hyderabad, IN
3 Department of Metallurgical Engineering, Andhra University, Visakhapatnam, IN
Source
Indian Welding Journal, Vol 51, No 2 (2018), Pagination: 66-74Abstract
Friction stir welding (FSW) is emerging as an alternative technique for joining high strength aluminium alloys as it eliminates the problems during fusion welding. In this work, the effect of post weld treatments (PWHT), viz., peak aging (T6) and retrogression and reaging (RRA) on the microstructure, mechanical properties, pitting corrosion and stress corrosion cracking (SCC) resistance of AA7075 aluminium alloy friction stir welds has been studied. An attempt also has been made to change the chemical composition of the weld nugget by adding boron carbide (B4C) nano powder with the aid of the FSW. Hardness and tensile properties were found to be better in PWHT – T6. Pitting corrosion and SCC resistances were improved in PWHT-RRA condition with negligible loss of strength when compared to PWHT-T6. RRA promotes coarse precipitation of the equilibrium phase η in the grains and sub grain boundaries, while maintaining a fine distribution of η' in the grain interiors. The increased strength and hardness in the peak aged (T6) condition was attributed to the presence of semi-coherent intermediate η' (MgZn2). With the addition of B4C nano powder to the weld nugget, hardness, tensile properties, pitting corrosion resistance and SCC resistance were further improved significantly when compared to the unreinforced weld nugget. PWHT-RRA treatment on the welds with B4C nano powder addition resulted in improved hardness of weld nugget which is attributed to the uniform distribution of strengthening precipitates in the matrix and powder strengthening. Pitting corrosion resistance, Tensile strength and SCC resistance was improved significantly in B4C added welds after RRA treatment when compared to the same welds without B4C addition.Keywords
Friction Stir Welding, FSW, AA7075 Aluminium Alloy, Pitting Corrosion, Stress Corrosion Cracking, Retrogression-Reaging, RRA, Boron Carbide (B4C).References
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- Venugopal T, Srinivasa Rao K, Prasad Rao K (2004); Studies on friction stir welded AA7075 aluminum alloy. Trans Indian Inst Metals, 57 (6), pp.659-663.
- Rao K Srinivasa, Rao K Prasad. (2004); Pitting corrosion of heat-treatable aluminium alloys and welds: a review, Trans Indian Inst Met, 57 (6), pp.593-610.
- Ranganatha R (2013); Multi-stage heat treatment of aluminum alloy AA7049. Trans Nonferrous Met Soc China, pp.1570-1575.
- Su JQ, Nelson TW, Mishra R, Mahoney M (2003); Microstructural investigation of friction stir welded 7050- T651 aluminium, Acta Mater, 51(3), pp.713-729.
- Hassan KhAA, Norma AF, Price DA, Prangnell PB (2003); Stability of nugget zone grain structures in high strength Al-alloy friction stir welds during solution treatment. Acta Mater, 51 (7), pp.1923-1936.
- Sullivan A, Robson JD (2008); Microstructural properties of friction stir welded and post weld heated 7449 aluminum alloy thick plate. Mater Sci Eng (A), 478, pp.351-360.
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- A Comparison Between Microstructure, Tensile Properties and Pitting Corrosion Resistance of Friction Stir and Gas Tungsten Arc Ferritic Stainless Steel Welds
Abstract Views :361 |
PDF Views:5
Authors
Affiliations
1 Defence Metallurgical Research Laboratory, Hyderabad, 500 058, IN
2 Department of Metallurgical Engineering, A. U. College of Engineering (A), Visakhapatnam - 530 003, IN
1 Defence Metallurgical Research Laboratory, Hyderabad, 500 058, IN
2 Department of Metallurgical Engineering, A. U. College of Engineering (A), Visakhapatnam - 530 003, IN
Source
Indian Welding Journal, Vol 46, No 4 (2013), Pagination: 59-64Abstract
In the present work an attempt was made to study the pitting corrosion susceptibility of AISI 430 ferritic stainless steel welds. Gas tungsten arc (GTA) welding and friction stir welding (FSW) processes were used to make welds. Potentio-dynamic polarization test was used to evaluate pitting corrosion resistance of the welds. Optical and electron microprobe analysis were used to study the microstructure and corrosion mechanism respectively. It was observed that the weld microstructure of GTA weld was predominately columnar. Friction stir weld exhibited fine equiaxed grain structure. Investigations clearly revealed that pitting corrosion resistance of friction stir weld zone was inferior compared to GTA weld in which breakdown potential was reduced by chrornium depletion. This was due to enhanced formation of intermetallic phase in friction stir welds compared to GTA welds. This was attributed to the slower cooling rate of friction stir welds, which results in longer exposure to the temperature range for precipitation during cooling cycle. Fine grain structure of friction stir weld has resulted in greater chromium depleted area than that of weld zone of GTA weld. In addition to the above, lower pitting corrosion resistance of friction stir welds was correlated to the formation of strain induced martensite in the nugget zone. Presence of residual stresses was also found to be affecting localized corrosion resistance by increasing number of active anode sites on the surface.
Keywords
Piiting Corrosion, Ferritic Stainless Steel, Welding, Microstructure, Sensitization.- Partially Melted Zone in Dissimilar Aluminium Alloy Welds-Effect of Prior Thermal Temper and Welding Process
Abstract Views :201 |
PDF Views:5
Authors
Affiliations
1 Department of Mechanical Engg., PVP Siddhartha Institute of Technology, Vijayawada-520007, IN
2 Defence Metallurgical Research Laboratory, Hyderabad-500 058, IN
3 Department of Metallurgical Engineering, Andhra University College of Engineering(A), Visakhapatnam - 530 003, IN
1 Department of Mechanical Engg., PVP Siddhartha Institute of Technology, Vijayawada-520007, IN
2 Defence Metallurgical Research Laboratory, Hyderabad-500 058, IN
3 Department of Metallurgical Engineering, Andhra University College of Engineering(A), Visakhapatnam - 530 003, IN
Source
Indian Welding Journal, Vol 43, No 2 (2010), Pagination: 32-40Abstract
Partially melted zone (PMZ) of aluminium alloy welds is an important region and requires careful attention. This is mainly because PMZ in these alloys is a weak link in the weldments and is significantly affected by welding parameters. Microstructural changes in PMZ are related not only to welding heat input and processes, but also depend on the initial thermal history of the alloy (for example, whether it is in O, T4, T6 orT87 condition etc.). Interestingly not many detailed studies are available in this respect. In the present work effect of prior thermal temper and welding process on the PMZ behaviour of dissimilar AA2014 and AA6061 alloy GTA and EB welds were studied. Grain coarsening and melting in PMZ is more when the alloys are welded in T4 temper than in O condition and AA2014 alloy is prone for liquation compared to AA6061 alloy which attributes high alloying element concentration in AA2014 side of the joint. EB welding proved to be efficient welding process compared to GTA welding in terms of resistance to liquation and better mechanical properties.
Keywords
Partially Melted Zone, Gas Tungsten Arc Welding, Electron Beam Welding, Dissimilar Alloy Welds.- Partially Melted Zone in Aluminium Alloy Welds
Abstract Views :245 |
PDF Views:5
Authors
Affiliations
1 Department of Metallurgical and Materials Engineering Indian Institute of Technology Madras, Chennai-600036, IN
1 Department of Metallurgical and Materials Engineering Indian Institute of Technology Madras, Chennai-600036, IN