Crack Profile

CRACK PROFILE OF Al 2014/Al2O3/15p TIG WELDED JOINT

M.N. Mazlee

School of Materials Engineering

Universiti Malaysia Perlis (UNIMAP)

Jejawi, 02600 Arau, Perlis

Malaysia

mazlee@unimap.edu.my

ABSTRACT

An investigation on the welded joint has been conducted to study the crack profile due to impact loading of aluminium 2014 reinforced with 15 vol. % of Al2O3 reinforcement particles. Tungsten Inert Gas (TIG) arc welding technique has been used to weld the joint. The testing of impact was done by means of Charpy impact test (V-notched specimen). The parameters have been used in TIG arc welding were 60 A current and 10 l/min flow rate. Three crack mechanisms were observed in the welded specimen namely interface separation between matrix and Al2O3 reinforcement particles, voids formation along the fracture surfaces and secondary crack formation.

INTRODUCTION

Aluminium metal matrix composites (AMMCs) is the potential advanced materials to be used in structural applications which attributed by the high specific stiffness and strength, good wear resistance, weight saving and also good weldability. Aluminium alloys reinforced with ceramic reinforcement particles can be welded by both fusion processes and solid state processes. The appropriate welding technique to be applied on the AMMCs plays an important role in terms of the structural integrity between the structural members or components.

Among the TIG research on aluminium alloys and AMMCs that have been conducted were concerning crack propagation [1], liquation crack [2], interfacial chemical reactions between the ceramic reinforcements and the molten matrix alloy [3,4] and welding parameter [5,6]. The objective of this paper is to study the crack profile due to impact loading on aluminium 2014 reinforced with 15 vol. % of Al2O3 reinforcement particles.

MATERIALS AND METHOD

The material used was Al 2014 (Al-Cu) matrix alloy reinforced with 15 vol. % of Al203 reinforcement particles in the form of rectangular bar. The composite was produced by casting method followed by hot extrusion process. The material was supplied by Duralcan Inc., San Diego, California, USA.

Tungsten Inert Gas (TIG) arc welding technique has been used to weld the square butt joint by using Lincoln Arc Welder (Idealarc) 250 equipment. Al-Si rod has been used as a filler material and tungsten thoria as an electrode. Figure 1 shows an X-ray fluorescene (XRF) analysis of Al-Si filler material. The testing of impact was done by means of Charpy impact test (V-notched specimen). The parameters have been used in TIG arc welding were 60 A current and 10 l/min flow rate. Optical microscope was used to identify and analyse the crack profile resulted from Charpy impact test.

RESULTS AND DISCUSSION

Figure 2 shows a crack profile at the edge of welded specimen. From Figure 2, it clearly shows that crack growth and crack propagation were only took place in the fusion zone which has a lower macro Vickers hardness reading (53.9 kg/mm2) relatively. Particles separation can be clearly observed in between a fusion zone and a heat affected zone. Particle clustering feature can be seen in a heat affected zone indicated by a rounded dotted line.

Figure 3 shows a secondary crack at the edge of welded specimen. A secondary crack was happened in almost straight crack line from the initiation of primary crack to the voids formation area. Sub crack in the matrix was clearly observed in the area which adjacent to the crack initiation along the interface separation between matrix and Al2O3 reinforcement particles. Crack branching feature was shown by crack branching out from the voids formation area. Crack branching can be explained as a crack which moved out from the secondary crack and produced sub crack. Further propagation of secondary crack was in the form of crack deflection. Crack deflection means a crack that avoids the particles along the crack route. However, a crack will stop at the end when a crack met a particle in the crack route which acts as a crack stopper.

CONCLUSION

Three crack mechanisms were observed in the welded specimen namely interface separation between matrix and Al2O3 reinforcement particles, voids formation along the fracture surfaces and secondary crack formation.

ACKNOWLEDGEMENT

The authors are grateful to MOSTE for financial support under IRPA Short Term Grant.

REFERENCES

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