Mechanical Properties and Microstructural Evolution of Bulk UFG Al 2014 Alloy Processed Through Cryorolling and Warm Rolling

doi:10.1007/s40195-018-0849-7

摘要/Abstract

关键词: Al alloys, Ultrafine grains, Fracture toughness

Abstract:

Tensile properties, microstructural evolution and fracture toughness of Al 2014 alloy subjected to cryorolling followed by warm rolling (CR?+?WR) have been investigated in the present study. The solution-treated (ST) Al 2014 alloy is cryorolled followed by warm rolling process at different temperatures (110, 170 and 210 °C). The mechanical properties and microstructural features of deformed and undeformed Al 2014 alloys were characterised by optical microscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The CR?+?WR samples at 170 °C showed an improved hardness (179 HV), tensile (UTS 499 MPa, YS 457 MPa) and fracture toughness (K_Q?=?37.49 MPa $\sqrt {\text{m}}$, K_ee?=?37.39 MPa $\sqrt {\text{m}}$ and J integral?=?33.25 kJ/mm²) with respect to ST alloy as measured from the tensile and fracture toughness test. The improved mechanical properties of CR?+?WR alloy are attributed to grain boundary strengthening, combined recovery and recrystallisation, precipitation hardening and dynamic ageing effect during the deformation. The precipitation of metastable spherical phase Al₂Cu was responsible for the improved tensile and fracture properties of fine-grained Al 2014 alloy observed in the present work.

Key words: Al alloys, Ultrafine grains, Fracture toughness

. [J]. Acta Metallurgica Sinica (English Letters), 2019, 32(7): 845-856.

Manoj Kumar Pathak, Amit Joshi, K. K. S. Mer, R. Jayaganthan. Mechanical Properties and Microstructural Evolution of Bulk UFG Al 2014 Alloy Processed Through Cryorolling and Warm Rolling[J]. Acta Metallurgica Sinica (English Letters), 2019, 32(7): 845-856.

图/表 13

Fig. 1 Mechanism of formation of UFG microstructure in precipitation hardenable Al alloy during cryo-SPD process [15]

Table 1 Chemical composition (wt%) of bulk Al 2014 alloy

Cu	Si	Mg	Mn	Fe	Zn	Al
4.8	1.0027	0.3454	0.7209	0.2158	0.1165	Balance

Fig. 2 Systematic diagram representing the process of cryorolling followed by warm rolling process

Fig. 3 Optical images of Al2014 alloy for a solution treatment, b cryorolling followed by warm rolling at 110 °C, c cryorolling followed by warm rolling at 170 °C, d cryorolling followed by warm rolling at 210 °C

Fig. 4 TEM micrographs with SAED pattern of Al 2014 alloy for a solution treatment, b cryorolling followed by warm rolling at 110 °C, c cryorolling followed by warm rolling at 170 °C along with TEM-EDX, d cryorolling followed by warm rolling at 210 °C along with TEM-EDX

Fig. 5 Variation in ultimate tensile strength (UTS), yield strength (YS) and percentage elongation before failure for Al 2014 alloy for different processed conditions

Fig. 6 Variation in strength (UTS and YS) and hardness of Al 2014 alloy for different processed conditions

Table 2 Mechanical properties of Al 2014 alloy at various material conditions

Processing condition	Vickers hardness (HV)	Yield strength (MPa)	Ultimate tensile strength (MPa)	Percentage elongation
ST	118	215	262	21
WR?+?110 °C	148	459	490	4.5
WR?+?170 °C	179	457	499	9.5
WR?+?210 °C	137	376	452	14

Fig. 7 Fractured surface morphology after tensile test of Al 2014 alloy for a solution treatment, b cryorolling followed by warm rolling at 110 °C, c cryorolling followed by warm rolling at 170 °C, d cryorolling followed by warm rolling at 210 °C

Fig. 8 Load versus Extension curve after three-point bend test for Al 2014 alloy at various processing conditions

Table 3 Fracture toughness parameters of Al 2014 alloy at various material conditions

Processing Condition	Apparent fracture toughness, K_Q (MPa $\sqrt m$	Equivalent energy fracture toughness, K_ee (MPa $\sqrt m$	Crack propagation energy/J integral (kJ/mm²)
ST	19.28	24.54	20.49
WR at 110 °C	35.36	35.73	31.67
WR at 170 °C	37.49	37.39	33.25
WR at 210 °C	23.22	27.73	20.45

Fig. 9 Procedure showing the measurement of equivalent energy fracture toughness (Kee) for ST Al 2014 alloy

Fig. 10 Fractographs of Al 2014 alloy after three-point bend test for a pre-crack zone, b solution-treated condition, c cryorolling followed by warm rolling at 110 °C, d cryorolling followed by warm rolling at 170 °C, e cryorolling followed by warm rolling at 210 °C

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