J DAVID RAJA SELVAM

Research ScholarUnder the Supervision of:

Dr. D. S. ROBINSON SMART

M.E.,Ph.D.

PROFESSOR

School of Mechanical SciencesKarunya UNIVERSITY.Coimbatore-T.N.-641114

Dr. D. S. ROBINSON SMART

M.E.,Ph.D.

PROFESSOR

School of Mechanical SciencesKarunya UNIVERSITY.Coimbatore-T.N.-641114

WELDING OF CAST Al/SIC/10p COMPOSITE MATERIAL BY TIG ARC WELDING USING

UNREINFORCED FILLER ALLOY (Al-Si)

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Abstract

Metal Matrix Composites (MMCs) are the leading research going on around the world in recent times. Welding of MMCs is an alternative to their Mechanical joining, since they are difficult to Machine. The TIG process is widely used for welding unreinforced aluminium alloys and although it is not the fastest process available, it is flexible, in that the deposition rate and heat input can be largely independent when filler is used. Welding current, welding speed, and the preheat temperature (300-350°C) affected the weld quality significantly. This study investigates the weldability of Al6061with SiC reinforced aluminium cast MMC. Statistical experiments were performed to identify the significant variables and their effects on the hardness, tensile, bending strengths and Non Destructive test.

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Introduction:– These metal matrix composites (MMCs) using aluminum as the matrix such as

Al with SiC particles reinforced in it (Al/SiCp), have found vast applications in automotive, aerospace, and marine and other allied fields, which have aggressive environments.

– Aluminium and silicon carbide, for example, have very different mechanical properties: Young's moduli of 70 and 400 GPa, coefficients of thermal expansion of 24 × 10−6 and 4 × 10−6/°C, and yield strengths of 35 and 600 MPa, respectively. By combining these materials, e.g. A6061/SiC/17p (T6 condition), an MMC with a Young's modulus of 96.6 GPa and a yield strength of 510 MPa can be produced [4].

– Among discontinuous metal matrix composites, stir casting is generally accepted as a particularly promising route, currently practiced commercially. Its advantages lie in its simplicity, flexibility and applicability to large quantity production. It is also attractive because, in principle, it allows a conventional metal processing route to be used, and hence minimizes the final cost of the product. This liquid metallurgy technique is the most economical of all the available routes for metal matrix composite production [5], and allows very large sized components to be fabricated.

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Experimentation:Casting of procedure of Al6061/SiC/10p:

The material used in this investigation was SiC particle reinforced 6061 aluminium composite fabricated by modified stir casting method to 8 mm thick plate. The volume fraction of SiC particle is 10%.

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Scraps of aluminium were preheated up to a temperature of 450 6 C and particles of silicon carbide up to a temperature of 1100 6 C in core drying oven. Crucible used for pouring of composite slurry in the mold was also heated up to 760 6 C.

The furnace temperature was first raised above the liquidus to melt the alloy scraps completely and was then cooled down just below the liquidus to keep the slurry in a semi-solid state. At this stage the preheated SiC particles were added and mixed manually. Manual mixing was used because it was very difficult to mix using automatic device when the alloy was in a semi-solid state.

After sufficient manual mixing was done, the composite slurry was reheated to a fully liquid state and then automatic mechanical mixing was carried out for about 10 minutes at a normal stirring rate of 750 rpm.

In the final mixing process, the furnace temperature was controlled within 760 ± 10 6 C. Pouring of the composite slurry has been carried out in the sand mould prepared according to the need for welding.

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Welding Procedure:Plates of 8mm thick Al-6061/sic/10p aluminum alloy (0.986wt.%Mg and

0.561wt.%Si) with a thickness of 8 mm were used in this study and a filler wire ER4043 (5.5wt.%Si), 2 mm in diameter, was employed to deposit the weld beads. Plates of base metal were machined to obtain the joint geometry shown in Fig. 1. Weld beads with a length of 250 mm were deposited using a semi-automatic GTA welding machine. The GTAW process parameters such as Pulse Current, Secondary Current, Pulse Frequency, Pulse Duty Cycle and % of He in Ar, play a major role in deciding the weld geometry. Manual pulsed GTAW was employed to join the metal plates together. The butt welding process was performed with ER4043 as filler metals. Welding parameters used were. Voltage (V), Travel Speed mm/min and gas flow rate.

Peak Current (Ip) 190 ABack Ground Current (Ib) 95 A

Speed 3.5 mm/sVoltage 12-15 vPulse frequency 50% of cycle timeShielding Gas Argon

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Experimental ResultsMechanical Properties:

Mechanical properties were characterized in terms of tensile and side bend test performance. In addition microstructure of representative welds was evaluated using. Metallurgical microscope (mag500x) tensile test was carried out using the sample prepared according to ASTM B557 section. The specimen was polished using abrasives paper to remove any scratches present. Two sets samples were prepared as per ASME section IX and average value attained is 146 N/mm2 all the test were conducted in a Universal testing machine. The scatter between the experimental data is below 2.5 %. The higher tensile strength of the welded samples is attributed to the residual stress due to their small dimensions. The present results are having higher tensile strength of welded samples compared to unwelded samples which were in agreement. The point of fracture always occurred in parent metal.

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TENSILE TEST RESULT

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Base Material RM (MPA)4043 POINT OF FRACTURE

6061/SiC/10p-1 148 Parent Metal6061/SiC/10p-2 140 Parent Metal606/SiC/10p-3 142 Parent MetalAverage 146

Fig 1 The microstructure of (Al+SiC10p) composites in the HAZ

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Microstructure:

The Sample was etched after polishing to reveal the microstructure clearly. The acids in the etchant attack the grain boundary and give a clear image of the size of the grain. To reveal the base metal, HAZ and weld metal, polished samples were etched with a solution of 75 HCl, 25 HNO3, 5 HF and 25 H2O (ml).

Fig 2. The Microstructure of Al\ SiC\10p in the HAZ

Fig 2. The Microstructure of Al\ SiC\10p in the HAZ

Conclusion

 

(1) During GTA welding of joints formed by reinforced Al/SiC/10p composite, it is necessary to deflect the arc toward the reinforced composite for compensating its lower weldability.

(2) The application of ER4043 filler metal inhibits the formation of Al4C3 at the matrix-particles interfaces of the composite metal.

(3) Failures during tensile tests always occurred through the HAZ of the reinforced Al606\SiC\10p, because the greater softening effect which occurred in them by the heat input.

(4) Tensile strengths of the different welded joints, in spite of the joints designs or of the arc input energy used, were always conditioned by the softening effect in the reinforced aluminium alloy HAZ, being approximately 146 MPa.

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Reference:

1. MBD Ellis, Int. Mater. Review 41 (1996) 41-58.

2. ASM 2 Metals Handbook, ASM International, Materials Park, OH, 1990.

3. K.A. Lucas, H. Clarke, Corrosion of aluminum-based metal matrix composites, John Wiley & Sons Inc., New York, 1993.

4. Kaiser Aluminum, Welding Kaiser aluminum, Kaiser Aluminum & Chemical Sales, Inc., Oakland, CA, 1978, pp. 8-1 – 8-21.

5. Midling O T, Grong Q. “A Process model for friction welding of Al-SiMg Alloys and Al-SiC metal matrix composite- Part II: HAZ Microstructure and strength evolution [J]. Acto metal Mater, 1994, 42(5): 1611-1623

6. T.S. Kumar, V. Balasubramanian, M.Y. Sanavullah, Influence of pulsed current tungsten inert gas welding parameters on the tensile properties of AA 6061 Aluminium alloy. Materials and Design, Vol. 28, n. 31, pp. 2080-2092, 2007.

7. J.R. Pickens, T.J. Langan, E. Barta, in: Proceedings of the III Aluminium–Lithium International Conference, Institute of Metals, Oxford, 1985, pp. 137–147.

8. P.P. Lean, Weldability of aluminium-SiC composites (AA6092/SiC/25p) by pulsed gas metal arc welding, Doctoral Thesis, Universidad Complutense de Madrid, December 2000.

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