Effect of Tool Pin Geometry and Process Parameters During FSW of Dissimilar Alloys of Mg

Yaknesh, S.; Sampathkumar, K.; Sevvel, P.

doi:10.1590/1980-5373-MR-2021-0508

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Article • Mat. Res. 25 • 2022 • https://doi.org/10.1590/1980-5373-MR-2021-0508 copy

Effect of Tool Pin Geometry and Process Parameters During FSW of Dissimilar Alloys of Mg

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Effect of two distinctive tool designs along with other tool related parameters including speed of traverse of tool and offset distance of tool pin during friction stir welding of dissimilar AZ91C and AZ31B alloys of Mg were investigated. Experimental recordings revealed that all the joints fabricated during 1^st set of investigations employing cylindrically tapered pin geometry and their offset distances being 0.5 mm or 1mm towards any one of the parent metals possessed flaws. Joint No: II-3 fabricated in 2^nd set of investigations by employing 15mm diameter inner shoulder tool with threaded cylindrical tapered pin geometry at a tool offset distance of 0 mm was found be free from flaws. This joint exhibited a tensile strength of 186 MPa which was 78.81% of AZ91C and 70.72% of another parent metal AZ31B. Existence of intermetallic phased constituents, namely, Mg₁₇Al₁₂ in several regions of fractured surfaces have contributed to the supplementary brittleness in the zone of nugget, and have reduced the tensile strength of the joint.

Keywords:
Tool pin geometry; speed of tool traverse; tool offset distance; brittle fracture; AZ31B; AZ91C

Material	Mn	Si	Zn	Ni	Fe	Cu	Al	Mg	Tensile Strength	Yield Strength	% of elongation
AZ31B	0.31	0.079	0.85	0.0049	0.005	0.051	3.15	Balance	263 MPa	178 MPa	11.7%
AZ91C	0.30	0.12	0.73	0.01	0.01	0.08	9.13	Balance	236 MPa	130 MPa	7.7%

1^st set of Investigations using Tool I					2^nd set of Investigations using Tool II
Tool offset distance from the line of joint	Speed of tool rotation (rpm)	Speed of tool traverse (mm/sec)	Axial force (kN)	Angle of tilt (degree)	Tool offset distance from the line of joint	Speed of tool rotation (rpm)	Speed of tool traverse (mm/sec)	Axial force (kN)	Angle of tilt (degree)
0.5 mm towards AZ31B side	1000	2	5	0.5⁰	0 mm	850	0.5	3.5	0⁰
1.0 mm towards AZ31B side	1000	2	5	0.5⁰	0 mm	850	1.0	3.5	0⁰
0 mm (matching with line of joint)	1000	2	5	0.5⁰	0 mm	850	1.5	3.5	0⁰
1.0 mm towards AZ91C side	1000	2	5	0.5⁰	0 mm	850	2.0	3.5	0⁰
0.5 mm towards AZ91C side	1000	2	5	0.5⁰	0 mm	850	2.5	3.5	0⁰

Joint No	Tool offset distance from line of joint & other employed parameters	Inferences from the structural appearances of the fabricated distinctive joints
I-1	Tool pin 0.5 mm towards AZ31B side; 1000 rpm; 2mm/sec; 5 kN; 0.5⁰	Uneven, hard weld surfaces revealing the difficulty experienced by tool shoulder in penetrating the joint areas
I-2	Tool pin 1.0 mm towards AZ31B side; 1000 rpm; 2mm/sec; 5 kN; 0.5⁰	Coarse & irregular weld surfaces onone side of joint revealing the lack of experience of sufficent amount of heat on that side
I-3	Tool pin 0 mm (exactly at line of joint); 1000 rpm; 2mm/sec; 5 kN; 0.5⁰	Presence of smooth surfaces over the majority regions along the area of joint
I-4	Tool pin 1.0 mm towards AZ91C side; 1000 rpm; 2mm/sec; 5 kN; 0.5⁰	Unwelded portions at the end of the area of joint revealing the hinderances being created against the flow of material from one side to another side
I-5	Tool pin 0.5 mm towards AZ91C side; 1000 rpm; 2mm/sec; 5 kN; 0.5⁰	Wobbly weld surfaces for longer areas revealing the difficulty experienced by tool shoulder in penetrating the joint areas

Joint No	Macro-structure	Micro-structure at the zone of nugget
I-1		Grain Size: 28.2 μm
I-2		Grain Size: 26.5 μm
I-3		Grain Size: 14.7 μm
I-4		Grain Size: 20.1 μm
I-5		Grain Size: 27.8 μm

Joint No	Speed of traverse of employed tool	Grain Size and Inferences
II-1	0.5 mm/sec	Grain Size: 15.8 μm. Tunnel defects at the bottom portion
II-2	1.0 mm/sec	Grain Size: 14.6 μm. Minute pores at the bottom poriton
II-3	1.5 mm/sec	Grain Size: 10.2 μm. Joint Surface free from flaws
II-4	2.0 mm/sec	Grain Size: 16.7 μm. Cavities at the bottom portion
II-5	2.5 mm/sec	Grain Size: 17.9 μm. Pores at the bottom portion

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