Analysis and Modeling of Friction Stir Processing-Based Crack Repairing in 2024 Aluminum Alloy

doi:10.1007/s40195-016-0489-8

Abstract

Abstract:

A friction stir processing-based method was used to repair cracks in the 2024 aluminum alloy plates. The temperature field and plastic material flow pattern were analyzed on the basis of experimental and finite element simulation results. Microstructure and tensile properties of the repaired specimens were studied. The results showed that the entire crack repairing was a solid-phase process and plastic materials tended to flow toward the shoulder center and then resulted in the repairing of cracks. Meanwhile, the coarse grain structures were refined in repaired zone (RZ), while the grains in thermal-mechanically affected zone and heat-affected zone were elongated and driven to grow up. Meanwhile, large phases are crushed into small particles and dispersed inside the RZ. Finally, the strength of the repaired specimens can be restored dramatically and their ductility can be partially restored. After heat treatment, the tensile properties of the repaired specimens can be further enhanced.

Key words: Friction stir processing, Crack repairing, Aluminum alloy, Microstructure, Hardness, Tensile properties

Jun-Gang Ren, Lei Wang, Dao-Kui Xu, Li-Yang Xie, Zhan-Chang Zhang. Analysis and Modeling of Friction Stir Processing-Based Crack Repairing in 2024 Aluminum Alloy[J]. Acta Metallurgica Sinica (English Letters), 2017, 30(3): 228-237.

Figures/Tables 16

Fig. 1 Outline of friction stir processing for repairing crack

Table 1 Chemical compositions of aluminum alloy 2024-T4 (wt%)

Si	Fe	Cu	Mg	Zn	Ti	Mn	Other		Al
0.5	0.5	3.8-4.9	1.2-1.8	0.3	0.15	0.3-0.9		Ni: 0.1, Fe + Ni: 0.5	Bal.

Table 2 Physical and mechanical properties of aluminum alloy 2024-T4

Melting range (°C)	Hardness (HV)		σ_b (MPa)	σ_s (MPa)	δ (%)
502-638		126	467	328	19.5

Fig. 2 Crack repairing process

Fig. 3 Dimension of the tensile specimen

Fig. 4 Temperature cycle curves from thermocouples (ω = 1100 rpm, v = 50 mm/min)

Fig. 5 a Temperature distributions from the FEM simulation, b temperature cycle curves at point 1, 2, 3 in a (ω = 1100 rpm, v = 50 mm/min)

Fig. 6 Plastic material flow patterns: a specimen top, b 1 mm underneath the specimen top, cthe longitudinal section (ω = 1100 rpm, v = 50 mm/min)

Fig. 7 Macrograph of the 2024-T4 repaired specimen

Fig. 8 Microstructures of a BM, b HAZ, c TMAZ, d RZ

Fig. 9 Micro-hardness profiles of the repaired specimen across the section (ω = 1100 rpm,v = 50 mm/min)

Table 3 Tensile properties of the specimens before and after repairing

Specimen	σ_b (MPa)	σ_0.2 (MPa)	δ (%)	φ (%)
Base material	465.8	307.5	19.5	24.6
Pre-cracked specimen	204.3	121.3	0.8	2.9
Repaired specimen^a	426.3	290.1	7.0	15.3
Repaired specimen after heat treatment^a	436.2	295.3	10.2	16.9

Fig. 10 Effect of rotating speed on the tensile properties of repaired specimens (v = 110 mm/min)

Fig. 11 Effect of advancing velocity on the tensile properties of repaired specimens (ω = 1100 rpm)

Fig. 12 Macro-fractures of the repaired specimens: a with delamination defect, b with few defects

Fig. 13 Micro-fractures of the repaired specimens

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