Effect of Submillimeter Variation in Plunge Depth on Microstructure and Mechanical Properties of FSLW 2A12 Aluminum Alloy Joints

doi:10.1007/s40195-019-00981-5

Abstract

Abstract:

Friction stir lap welding was conducted on 2 mm?+?2 mm sheets of aluminum alloy 2A12-T4. The plunge depth (PLD) was designed as 2.45-2.58 mm, which was varied in submillimeters as 2.45, 2.50, 2.53, 2.55, and 2.58 mm, and the axial force was recorded in the welding process. The results show that the PLD fluctuation in submillimeters causes significant variation in the axial force and affects the voids (i.e., Void I and Void II), hook, and effective sheet thickness (EST), among which Void I is the main factor that affects the EST. The fracture load-PLD function in the tensile shear test of the joints follows the rule of the EST-PLD function. An optimized PLD is approximately 2.55 mm, at which the EST reaches 1.71 mm, corresponding to a peak fracture load of 11.03 kN. Thus, a PLD of 2.55 mm is suggested with a tolerance of 0.02 mm, corresponding to a fracture load of 9.6-11.0 kN, i.e., within a fluctuation of 12%.

Key words: Submillimeter, Plunge depth, Mechanical properties, Friction stir lap welding

Dan Chen, Jinglong Li, Huaxia Zhao, Zhejun Tan, Jiangtao Xiong. Effect of Submillimeter Variation in Plunge Depth on Microstructure and Mechanical Properties of FSLW 2A12 Aluminum Alloy Joints[J]. Acta Metallurgica Sinica (English Letters), 2020, 33(1): 165-171.

Figures/Tables 11

Table 1 Nominal chemical composition of 2A12-T4 Al alloy (wt%)

Cu	Si	Fe	Mn	Mg	Ni	Zn	Ti	Al
3.8-4.9	0.50	0.50	0.30-0.9	1.2-1.8	0.10	0.30	0.15	Bal.

Fig. 1 Dimensions and configuration of the tensile shear samples

Fig. 2 Axial force evolutions showing a welding stage classification in a welding cycle, b the effect of the PLD

Fig. 3 Correlation between the axial force and the PLD

Fig. 4 Cross section morphologies of the joint welded at PLDs of a 2.45 mm, b 2.50 mm, c 2.53 mm, d 2.55 mm, e 2.58 mm

Fig. 5 Morphologies of the hook defects on the AS of the joint welded at PLDs of a 2.45 mm, b 2.50 mm, c 2.53 mm, d 2.55 mm, e 2.58 mm

Fig. 6 Measurements of the heights of the hook and the EST as functions of the PLD

Fig. 7 Microstructures of the TMAZ/NZ interface on the AS of the joint welded at PLDs of a 2.45 mm, b 2.50 mm, c 2.53 mm, d 2.55 mm, e 2.58 mm

Fig. 8 Mechanical properties of the joints showing a the microhardness distributions, b the average hardness as a function of PLD, c the fracture load as a function of PLD

Fig. 9 Crack path and fracture morphology of the joint welded at a PLD of 2.45 mm

Fig. 10 Crack path and fracture morphology of the joint welded at a PLD of 2.55 mm

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