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

doi:10.1007/s40195-018-0849-7

Abstract

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

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.

Figures/Tables 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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