Influence of Pre-strain on the Mechanical Properties of A6111-T4P Sheet with Bake Hardening

doi:10.1007/s40195-015-0247-3

Abstract

Abstract:

A6111 is an aluminum alloy, which exhibits good formability and excellent bake hardening property. This study aimed to reveal the influence of strain path, pre-strain orientation (α) as well as pre-strain level on the mechanical properties of A6111-T4P sheet under bake treatment through uniaxial tension test. (0-5)% pre-strain, 150-170 °C bake temperature and 20-30 min bake time were considered in the study by referring to the actual production process. The results show that both pre-strain level and strain path play significant roles in improving the material properties. In the condition that tensile orientation (β) parallel with pre-strain orientation (β = α), the yield strength can be remarkably improved, and much higher parameter of n in Hockett-Sherby model can be obtained than those when tensile orientation non-parallel with pre-strain orientation (α ≠ β). In addition, when the pre-strain level, paint bake process were settled and β = α, the curves obtained in five tension orientations are similar in the plastic deformation stage.

Key words: Aluminum, alloy, Pre-strain, Bake, hardening, Mechanical, properties

Shan-Shan Li, Jie-Shi Chen, Jun Chen, Cedric Xia, Danielle Zeng. Influence of Pre-strain on the Mechanical Properties of A6111-T4P Sheet with Bake Hardening[J]. Acta Metallurgica Sinica (English Letters), 2015, 28(6): 678-683.

Figures/Tables 10

Table 1 Experimental procedure

Experimental process	Control factor	Factor level
Uniaxial pre-strain	Pre-strain level	0%, 2%, 5%
Uniaxial pre-strain	Pre-strain orientation	0°, 30°, 45°, 60°, 90°
Bake	B1	170 °C for 30 min (170 °C/30 min)
	B2	170 °C for 20 min (170 °C/20 min)
	B3	150 °C for 30 min (150 °C/30 min)
Tensile test	Tensile orientation	0°, 30°, 45°, 60°, 90°

Table 2 Chemical compositions of the experimental alloy (wt%)

Al	Mg	Si	Cu	Mn	Fe	Zn	Ni	Other
97.625	0.991	0.53	0.344	0.07	0.418	0.009	0.003	Max. 0.01

Fig. 1 Heat treatment process before pre-strain

Fig. 2 The definition of pre-strain orientation and tensile orientation

Fig. 3 Stress-strain curves obtained under different pre-strain conditions (engineering strain = pre-strain level + post-paint bake elongation)

Fig. 4 The fitting parameters of n under B1 condition

Fig. 5 Yield stress after paint bake in different pre-strain level

Fig. 6 Average yield stress growth rate under different pre-strain condition: a pre-strain = 2%, b pre-strain = 5%

Fig. 7 Elongation under different pre-treatment conditions: a pre-strain = 2%, b pre-strain = 5%

Table 3 The hardening value in B3 condition when the pre-strain was 5% (MPa)

Condition	TD0°	TD30°	TD45°	TD60°	TD90°	Avg. 2	Stdev. 2
PD0°	78.1	59.3	62.2	60.8	58.9	63.9	8.1
PD30°	87.2	92.8	81.9	76.3	78.2	83.3	6.7
PD45°	85.3	86.2	99.4	86.7	78.4	87.2	7.6
PD60°	88.7	87.8	89.9	105.3	89.7	92.3	7.3
PD90°	59.3	59.8	59.2	64.2	77.4	64.0	7.8
Avg. 1	79.7	77.2	78.5	78.7	76.5
Stdev. 1	12.1	16.3	17.4	18.1	11.1

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