Study on Mechanical Properties of Aluminum Alloy AA 6351-T6 using TIG Welding

Size: px

Start display at page:

Download "Study on Mechanical Properties of Aluminum Alloy AA 6351-T6 using TIG Welding"

Brent Owens
6 years ago
Views:

1 ISSN (ONLINE): 2-78, ISSN (PRINT): Volume-6, Issue-2, March-April 16 International Journal of Engineering and Management Research Page Number: Study on Mechanical Properties of Aluminum Alloy AA 61-T6 using TIG Welding Kumar Gaurav 1, Sunil Kumar 2 1 Research Scholar, Department of Mechanical Engineering, PPIMT, HISAR, (Haryana), INDIA 2 Assistant Professor in Department of Mechanical Engineering, PPIMT, HISAR, (Haryana), INDIA ABSTRACT Preparations of AA61 T6 for nine specimens were cut of dimension 1x1x6 with the use of cutter from nine welded specimens. That specimen has weld bead at its centre and HAZ zone. The specimens were subjected to coarse grinding on bench grinder. Coarse grinding is required to planarize the specimen. Then the specimens were filed using hand file in one direction to remove burs and pre preparation for polishing. Specimens were polished initially on emery paper of 6 grit grade for rough polishing then on 1 grit grade for fine polishing followed with grit grade emery paper and then grit grade for highly fine polishing. After pre polishing specimens were polished on satin cloth for smooth and shiny surface finish on motor driven polishing disk. Fine polishing was done in a cloth polishing mill using diamond paste as polishing agent. The purpose of final polishing is to remove only surface damage. If the damage from these steps is not complete, the rough polishing step should be repeated. Finally the samples were etched for microstructure study. Keywords--- Aluminum Alloy Aa 61-T6, Mechanical Properties, Tig Welding I. INTRODUCTION Welding is a process for joining different materials. The large bulk materials that are metals, their alloys and other materials such as thermoplastics are joined by welding process. Welding process may be defined as join of similar and dissimilar materials by means of heat. Pressure may be also employed in many processes. There are various ways of classifying the welding and allied processes on the basis of Source of heat, i.e., flame arc, etc. Type of interaction i.e. liquid/liquid (fusion welding) or solid/solid (solid state welding). In general various welding and allied processes are classified as follows: 1. Gas welding (a) Air-acetylene welding, (b) oxy-acetylene welding, (c) oxy-hydrogen welding (d) pressure gas welding 2. Arc welding (a) Carbon Arc welding, (b) shielded metal Arc welding (c) Flux cord Arc welding (d) submerged Arc welding (e) TIG (GTAW) welding (f) MIG (GMAW) welding (g) plasma Arc welding, (h Electro slag welding and electro gas welding (i) stud Arc welding 3. Resistance welding (a) Spot welding, (b) seam welding, (c) projection welding, (d) resistance Butt welding, (d) flash butt welding (f) percussion welding, (g) High frequency Resistance welding 4. Solid state welding (a) Cold welding, (b) diffusion welding, (c) Explosive welding, (d) forge welding,(e) friction welding, (f) hot pressure welding,(g) roll welding(h) ultrasonic welding. Thermo chemical welding process (a) Thermit chemical welding, (b) atomic hydrogen welding 6. Radiant energy welding process (a) Electron beam welding (b) laser beam welding Tungsten inert-gas welding, as the name suggests, is a process in which the source of heat is an arc formed between a non-consumable tungsten electrode and the work piece, and the arc and the molten puddle are protected from atmospheric contamination (i.e. oxygen and nitrogen) with a gaseous shield of inert-gas such as argon, helium or argon-helium mixture. Filler metal, if required, is added externally to the arc in the form of bare wire by the welder. It is often referred to in abbreviated form as TIG welding some authors prefer to call it inert gas tungsten arc welding. This is a transformer, a rectifier or a motor generator set, depending on the application. The 818 Copyright 16. Vandana Publications. All Rights Reserved.

2 ISSN (ONLINE): 2-78, ISSN (PRINT): power source characteristic is essentially drooping type, which means that power sources designed for and used in manual metal arc welding A (MMAW) can be directly used for TIG welding. For better arc stability and a smooth arc, the OCV of the power source should be between 7 and 8 V (RMS). Argon is monatomic gas (i.e. its molecule consists of one atom instead of two atoms in the case of common gases like oxygen, nitrogen, chlorine, etc.) it is extracted from the atmosphere by liquefaction of air and refined to 99.9% purity. It is supplied as compressed gas in cylinders. II. LITERATURE REVIEW A.F. Norman, V. Drazhner, P.B. Prangnell (1999) studied on Effect of welding parameters on the solidification microstructure of autogenous TIG welds in an AI-Cu Mg-Mn alloy. The weld metal microstructures of autogenours TIG welds have been investigated for a welding condition using an AI-Cu-Mg-Mn alloy. It was found that a combination of high welding speeds and low power densities porvied the thermal conditions required for the nucleation and growth of equiaxed grains in the weld pool, providing heterogeneous nucleation sites are available. The most likely origin of the nucleants is from a combination of dendrite fragments and TiB2 particles that survive in the weld pool. The finest microstructure was observed in the centre of the weld pool. The finest microstructure was observed in the centre of the weld and in attributed to the higher cooling rates which operate along the weld centerline. Composition profiles across the dendrite side arms were measured in the TEM and were found to follow a scheil type segregation behavior where there is negligible back diffusion in the solid. The measured core concentration of the dendrite side arms was found to rise with increasing welding speed and was attributed to the formation of significant under cooling ahead of the primary dendrite tip, which enriched the liquid surrounding the dendrite side arms. The sheet thickness was 1.6 mm and simple butt geometry of AA 24 was used for each experiment. The experiments were designed such that, as the welding speed was increased, the welding current was also increased to just maintain full peroration of the weld. M. Awang studied on The effects of process parameters on steel welding response in curved plates. The arc welding process was simulated using finite Element Method (FEEM) Program ANSYS. The simulations were carried out using a two step process; nolinear heat transfer that produces the dynamic temperature distribution throughout the weld seam and the plates, and the elasto-plastic analysis, which yields residual stresses, strains, and displacement. The birth and death element feature was used in the finite element model to simulate the welding process. The responses along several longitudinal cross sections were obtained after the plate cooled down to room temperature. The result shows that all parameters, except for the gap between the plates have a significant effect on the responses. Relationships between the parameters and the responses have been drawn based on the simulation result. III. MATERIALS USED Chemical composition of the base metals, filer metal and shielding gas used in the experiments is given below. These materials were selected because of their availability. And wide usage in the industry 3.1Base Metals Probably the most important factor relating to the weldability of aluminium alloys is their chemical composition. The term weldability has no universally accepted meaning and the interpretation place upon term varies widely according to individual viewpoint. The American welding society defines weldability as the capacity of a metal to be welded under the fabrication conditions imposed, into a specific, suitably designed structure, and to perform satisfactorily in the intended service. During the experiments AA 61-T6 plates used. AA 61-T6 aluminium ally with the dimensions of 76 mm (1) x 4 mm (w) x 6 mm (t) was selected to represent the aluminium alloy. It contains silicon, magnesium and manganese as main alloying element. The chemical composition of AA 61- T6 aluminium alloy is given at table Table:3.1 Chemical composition of base metal. Copper.34 Magnesium.896 Silicon.4 Iron.479 Manganese.6 Nickel.6 Zinc. Lead. Tin.22 titanium Copyright 16. Vandana Publications. All Rights Reserved.

3 ISSN (ONLINE): 2-78, ISSN (PRINT): chromium. Aluminium The weldability of alulminium alloy, discounting such factors as thickness and joint geometry, is a function of the silicon, magnesium and manganese contents. All carbon steels can be welded by metal-arc welding. Where the silicon content does not exceed.% and magnesium does not exceed.896 depending on the thickness of the material, this material can be welded by TIG welding which will assure proper penetration and fusion. Filler Metal The majority of arc welding is done with the addition of a filler metal that plays a major role in determining the compostion and microstructure of the weld. The consumable electrode wire was selected based on properties and characteristics of the base material, weld dimensions. AA 414 wire electrode having 2.8 mm diameter was usem as filer metal. The following table entails the chemical compostion of the filer material according to AWS used in TIG: Weld,metal Chemistry (%) Table:3.2 Chemical composition of filler material Si Fe Cu Mn Mg Zn Ti Al max.3max.max.max.1max.max 9max Shielding gas The main function of the shielding gas is to displace the air in the weld zone and thus prevent contamination of the weld metal by nitrogen, oxygen and water vapour the selection of the best shielding gas is based on consideration of the materials to be welded and type of metal transfer that will be used. For the experiments, argon is used because it is only available in India and also produces deeper penetration. Welding condtions and process paramenters Gas tungsten Arc welding is governed by a set of factors and condtions such as amount of current, welding speed, polarity, etc which are called as process parameters. The optimum process parameters generally maintained during the welding processes for aluminium alloy are given in table. Table: 3.3 Welding conditions and process parameters Parameters TIG Joints Butt Joint (double V-groove) Polarity DCRP Arc Voltage Constant Welding speed Constant Welding current(amp) 8,1,1 Electrode Diameter()mm 2.8 Shielding Gas Argon Gas flow rate (it/min) 1,3, IV. EXPERIMENTAL PROCEDURE Aluminium alloy plates (aa 61-T6 )with the dimesnsions 76 mm (1)x 4 mm (w)x 6 mm(t)were prepared with double V butt joint 4 deg groove angle as welding current and gas flow rate are taken as process variables. The welding current values were taken as 8, 1 and 1 ampere and the gas flow rate values were 1,3 and lt/min. Then plates were welded through TIG welding by using 2.8 mm AA443 wire electrode and Ar gas. Nine experiments were performed. Table:4.1 Different conditions for welding Specimen No. Welding Current (amp) Gas flow rate(lt/min) 8 Copyright 16. Vandana Publications. All Rights Reserved.

4 ISSN (ONLINE): 2-78, ISSN (PRINT): V. RESULT AND DISCUSSION The hardness of base metal (unwelded parent metal) in its initial condition was 26 HRB. Table represents the comparison between the hardness of all the specimens at all measuring locations. Rockwell hardness with respect to welding parameters Specimen N Table:.1 (HRB) at different Location points 1 2 3(HAZ) 4(WB) HAZ From the table, I found that hardness of Heat affected Zone (location-3&) is greater than weld bead (location-4) of Location 1,2,6 and 7 it is less than weld bead. increase from weld centre to Heat Affected Zone and further it decrease when move to base metal side. It is clean for the Table.1 that the specimen n.4 has the greater hardness at weld bead among all the specimen and the specimen no 9 has the lowest hardness at weld bead. This shows that at 8 amp current and 1lt/mn gas flow rate, the highest hardness at weld bead were obtained and at 1 amp current and lt/min gas flow rate, the lowest hardness at weld bead were obtained. Different graphs show variation in hardness when move to base metal from weld centre in a TIG welded butt joint of AA61 T6 aluminium alloy. 821 Copyright 16. Vandana Publications. All Rights Reserved.

9 ISSN (ONLINE): 2-78, ISSN (PRINT): Fig.9 variation of specimen no.9 VI. CONCLUSION In the present study, hardness, impact energy and microstructure of AA61 t6aluminium alloy plates welded by TIG were determined and observed. From this investigation, the following important conclusions have been derived: 1. is lower in the base metal (WM) region compared to the HAZ and weld bead regions. The hardness increase after welding and the highest hardness obtained at 1 amp and lt/min parameters. Among the entire nine specimen, the specimen no has highest hardness and specimen no 9 has lowest hardness. 2. The specimen no 6 with 1 ampere current and it/min gas flow rate showed the highest fracture energy in the impact test. The specimen no 9 with 1 ampere and lt/min shows the lowest fracture energy in the impact test. 3. As the specimen no shows the highest hardness among all the other specimen and that was only related to the microstructure. The microstructure shows the small and fine grains which means it increase the hardness. Decreasing size of the grains improve the strength and ductility of aluminium alloy. REFERENCES [1] Norman, A.F., V. Drazhner and P.B. Prangnell, Effect of welding parameters on the solidification microstructure of autogenous TIG welds in an Al-Cu-Mg-Mn alloy, Materials science and Engineering: A9.1 (1999): 3-64 [2] Chen, Bai-Qiao. Prediction of Heating Induced Temperature Fields and Distortions in steel plates. (11) [3] Manti Rajesh, and D.K. Dwivedi. Microstructure of Al-Mg-Si weld joints produced by pulse TIG welding. Material and manufacturing process 22.1 (7): [4] Preston, R.V., et al. physically based constitutive modeling of residual strees development in welding of aluminium alloy 24. Acta Materialia 2.17 (4): [] Miyasaka, F.,Y.Yamane, and Y. Ohji. Development of Circumferential TIG Welding & joining 1. (): [6] Senthil Kumar, T.,V. Balasubramanian, and M.Y. Sanavullah. Influence of Pused current tungsten intert gas welding parameters on the tensile properties of AA 661 aluminium alloy, Materials & design 28.7 (7): [7] Manti Rajesh, D.K. Dwivedi, and A. Agarwal. Microstructure and hardness of Al-Mg-Si weldments produced by pulse GTA welding. The International Journal of advanced Manufacturing Technology 36.3 (8): [8] Dutta, Parikshit, and Dilip Kumar Prathihar. Modeling of TIG welding process Using conventional regression analysis and neural network-based approaches. Journal of material processing technology (7) Copyright 16. Vandana Publications. All Rights Reserved.

WELDING TECHNOLOGY AND WELDING INSPECTION

WELDING TECHNOLOGY AND WELDING INSPECTION PRESENTED BY: GOPAL KUMAR CHOUDHARY SVL ENGINEERING SERVICES CHENNAI CONTENTS: DEFINATION TYPES OF WELDING ELECTRODE GEOMETRY EQUIPMENT QUALITY PROCESS SAFETY