Improving the Weld Formation and Mechanical Properties of the AA-5A06 Friction Pull Plug Welds by Axial Force Control

doi:10.1007/s40195-020-01015-1

Abstract

Abstract:

In the present study, the weld formation and mechanical properties of the AA-5A06 friction pull plug welded (FPPW) joints were improved by controlling the axial force history. Several defect-free FPPW joints were made successfully by using the welding parameters of 15-20 kN/s axial loading rate, 20-30 kN axial welding force and 6-7 mm axial feeding displacement. The results indicated that using higher axial loading rate and axial welding force produced more stable heat generation and shorter frictional heating time between the frictional interface. In this case, the plastic flow of the materials around the hole could be further improved since the axial feeding displacement of the plug was increased. The maximum ultimate tensile strength (UTS) and elongation of the FPPW 5A06 joints were 314 MPa and 4.8%, respectively. The thermal mechanically affect zone (TMAZ) had the lowest hardness value throughout the joint and was found as the fracture location to all the tensile samples. The softening of TMAZ was mainly caused by the weakening of the cold work hardening and the coarsening of grains.

Key words: Friction pull plug welding, Parameter optimization, Microstructures, Mechanical properties

Jinyong Gao, Lijun Yang, Lei Cui, Peng Lu, Jun Yang, Yanjun Gao. Improving the Weld Formation and Mechanical Properties of the AA-5A06 Friction Pull Plug Welds by Axial Force Control[J]. Acta Metallurgica Sinica (English Letters), 2020, 33(6): 828-838.

Figures/Tables 16

Fig.1 Schematic diagram of friction pull plug welding (FPPW)

Table 1 Chemical composition of 5A06-H112 aluminum alloy (wt%)

Material	Mg	Si	Fe	Zn	Ti	Mn	Cu	Be	Al
5A06-H112	6.8	0.4	0.4	0.2	0.1	0.8	0.1	0.005	Bal.

Fig.2 Details of material used in FPPW process, a, b the geometry parameters of the plug and the hole (mm), c schematic illustration of FPPW process

Fig.3 Welding parameters of 5A06 aluminum alloy FPPW

Table 2 Welding parameters of 5A06 aluminum alloy FPPW

Sample	Rotating speed (rpm)	Axial feed displacement (mm)	Axial loading rate (kN/s)	Axial welding force (kN)	Forging force (kN)
CASE 1	7000	6	10	25	25
	7000	6	15	25	25
	7000	6	20	25	25
CASE 2	7000	6	15	20	20
	7000	6	15	25	25
	7000	6	15	30	30
CASE 3	7000	5	15	25	25
	7000	6	15	25	25
	7000	7	15	25	25

Fig.4 Cross sections of the joints welded with different axial loading rates, a 10 kN/s, b 15 kN/s, c 20 kN/s, d, e are the details of lack of bonding defects as marked in Fig.4a

Fig.5 Cross sections of the joints welded with different axial welding force, a 20 kN, b 25 kN, c 30 kN

Fig.6 Cross sections of the joints welded with different axial feeding displacement, a 5 mm, b 6 mm, c 7 mm, d, e are the details of lack of bonding defects as marked in Fig.6a

Fig.7 Microstructure in different regions of the joint welded in Case 1(b): a bonding interface, b PM, c RZ, d TMAZ, e HAZ, f BM

Fig.8 Second-phase particles in different regions of the joint: a PM, b RZ, c bonding interface, d TMAZ, e HAZ, f BM, g EDS of particles near the bonding interface, h EDS results of particle a, i EDS results of particle b

Fig.9 Morphologies of second particles at the BM and bonding interface of the joint: a second particles at the BM, b second particles near the bonding interface, c diffraction pattern of Al6FeMn, d diffraction pattern of Al3Mg2

Fig.10 Hardness distribution of 5A06 FPPW joint welded with the parameters used in Case 1(b)

Fig.11 UTS and elongation of the joints welded with different axial loading rates

Fig.12 UTS and elongation of the joints welded with different axial welding forces

Fig.13 UTS and elongation of the joints welded with different axial feeding displacements

Fig.14 Fracture morphology of joints failed with different strengths: a Case 2(c), b Case 2(b), c Case 3(a)

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