Improved Fracture Toughness of Cryorolled and Room Temperature Rolled 6082 Al Alloys

doi:10.1007/s40195-014-0057-z

Abstract

Abstract:

In the present work, 6082 Al alloy has been rolled to 40% and 70% thickness reductions at the cryogenic and room temperatures for the improvement in mechanical and fracture toughness properties. All cryorolled samples are subjected to aging at different temperatures, i.e., 140, 160, and 190 °C to improve the strength, ductility, and fracture toughness. The microstructures of the cryorolled (CR) and room temperature rolled (RTR) alloy after 40% and 70% thickness reductions are characterized by FE-SEM to reveal the modes of failure. The results show that the starting bulk Al alloy specimen is fractured in total ductile manner, consisting of well-developed dimples over the entire surface. The mechanical properties and fracture toughness of the 70% CR alloy are found better than 70% RTR alloy due to higher dislocations density and formation of sub-grain structures in the CR alloy.

Key words: 6082 Al alloy, Rolling, Mechanical properties, Fracture toughness, J-Integral, Material characterization

Vineet Kumar, I. V. Singh, B. K. Mishra, R. Jayaganthan. Improved Fracture Toughness of Cryorolled and Room Temperature Rolled 6082 Al Alloys[J]. Acta Metallurgica Sinica (English Letters), 2014, 27(2): 359-367.

Figures/Tables 15

Fig. 1 a Dimensions of the CT specimen for fracture toughness test, b actual broken CT specimen

Fig. 2 Loading position of the fracture toughness test

Fig. 3 Plot of load with load line displacement (LLD) for bulk alloy a, 40% CR alloy b, 70% CR alloy c, 40% RTR alloy d, 70% RTR alloy e

Fig. 4 Plots of Vicker’s hardness versus. aging time: a 40% CR alloy, b 70% CR alloy

Fig. 5 Optical micrographs of bulk alloy a, 40% CR alloy b, 70% CR alloy c, 40% RTR alloy d, 70% RTR alloy e

Fig. 6 TEM images of bulk alloy a, 40% CR alloy b, 70% CR alloy c, 40% RTR alloy d, 70% RTR alloy e

Table 1 Mechanical properties of the initial, CR, and RTR 6082 Al alloy

Sample	Yield strength, σ_y (MPa)	Tensile strength, σ_s (MPa)	Elongation (%)
40%-CR	370.0	350.6	13.5
40%-RTR	330.0	358.6	13.9
70%-CR	380.0	388.8	14.0
70%-RTR	350.0	380.8	11.2
Initial alloy	260.3	340.0	12.0

Fig. 7 Hatched area used for J-calculation

Table 2 Measured values of elastic–plastic fracture toughness (J1C)

Crack extension (mm)	Elastic–plastic fracture toughness (J_1C), MPa m^1/2
	Bulk alloy	CR		RTR
	Bulk alloy	40%	70%	40%	70%
0.38	4.15	10.00	12.80	8.30	10.29
0.70	6.84	12.50	15.00	10.20	12.80
1.01	7.34	14.30	16.40	12.20	14.92
1.25	7.84	15.56	17.80	13.75	16.96
1.48	8.43	16.48	19.00	15.51	18.20
1.63	8.58	17.25	20.12	16.60	19.10
1.64	8.64	18.04	21.20	16.80	19.30
2.03	8.39	18.50	21.40	16.20	19.50
2.04	7.99	18.20	21.20	15.10	19.40

Fig. 8 Fracture toughness of bulk, 40% CR, 70% CR, 40% RTR, and 70% RTR alloy

Fig. 9 FE-SEM images of the fracture surface of the bulk alloy: a transition region (fatigue pre crack and fracture), b fracture surface (enlarged view)

Fig. 10 FE-SEM images of the fracture surface of 40% CR alloy: a transition region (fatigue pre crack and fracture), b fracture surface (enlarged view)

Fig. 11 FE-SEM images of the fracture surface of 70% CR alloy: a transition region (fatigue pre crack and fracture), b fracture surface (enlarged view)

Fig. 12 FE-SEM images of the fracture surface of 40% RTR alloy: a transition region (fatigue pre crack and fracture), b fracture surface (enlarged view)

Fig. 13 FE-SEM images of the fracture surface of 70% RTR alloy: a transition region (fatigue pre crack and fracture), b fracture surface (enlarged view)

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