Global and local constitutive behaviors of friction stir welded AA2024 joints

doi:10.1016/j.jmst.2017.02.010

Abstract

Abstract:

In this study, the global and local tensile properties of friction stir welded AA2024 joints were measured with the aid of digital image correlation (DIC) method. A novel model was proposed to describe the global and local constitutive behavior of the joints based on DIC data. Different from conventional division of the zones across the joints, a new reasonable division was proposed, i.e. four zones including central low hardness zone (CLHZ), first heat affected zone (HAZ-I) close to TMAZ, second heat affected zone (HAZ-II) close to base metal (BM) and BM in term of the characteristic distribution of hardness. Results reveal that local true stress-true strain curves are different in each zone of interest. Plastic deformation of the joints is concentrated in CLHZ, where the lowest yield stress and the largest strain appear. Therefore, strain localization and necking occur here in a sequence. In addition, the global true stress-true strain curves and yield stresses at various ratios of the width of CLHZ zone to the gauge length are accurately predicted using the proposed constitutive model of the joints.

Key words: Friction stir welding, Aluminium alloy, Tensile property, Constitutive behavior

Niu Pengliang, Li Wenya, Zhang Zhihan, Yang Xiawei. Global and local constitutive behaviors of friction stir welded AA2024 joints[J]. J. Mater. Sci. Technol., 2017, 33(9): 987-990.

Figures/Tables 8

Fig. 1. Cross-sectional macrostructure and hardness distribution of the joint: (a) macrostructure, (b) division of the joint depending on the hardness distribution.

Fig. 2. Global and local true stress-strain curves of the joint.

Fig. 3. Hardness and tensile strain distribution in the middle cross-section of the joint for different nominal stresses.

Fig. 4. Correlation between local yield stress (calculated from the stress-strain curve of different locations) and hardness.

Fig. 5. Schematic view of welded specimen under transverse tensile load corresponding to joint hardness.

Table 1 Local and global mechanical properties of the joint.

Weld region	L₀ (mm)	E (GPa)	σ_s (MPa)	UTS (MPa)	FE (%)	K (MPa)	n
Global	L₀ = 50.0	72	305	470	8.2	710.2	0.165
BM	2L₀₁ = 25.9	72.1	322	543	17.7	728.6	0.174
HAZ-II	2L₀₂ = 6.6	70.1	306	N/A	N/A	727.8	0.169
HAZ-I	2L₀₃ = 7.3	70.5	308	N/A	N/A	719.5	0.165
CLHZ	L₀₄ = 10.2	69.5	291	N/A	N/A	722.0	0.180

Fig. 6. Predicted true stress-strain curve compared with experimental data.

Fig. 7. Variation of predicted yield stress with the proportion of CLHZ in the gauge length.

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