Molecular Dynamics Simulations and Experimental Investigations of Atomic Diffusion Behavior at Bonding Interface in an Explosively Welded Al/Mg Alloy Composite Plate

doi:10.1007/s40195-017-0628-x

Abstract

Abstract:

In this study, 6061 aluminum alloy and AZ31B magnesium alloy composite plate was fabricated through explosive welding. Molecular dynamics (MD) simulations were conducted to investigate atomic diffusion behavior at bonding interface in the Al/Mg composite plate. Corresponding experiments were conducted to validate the simulation results. The results show that diffusion coefficient of Mg atom is larger than that of Al atom and the difference between these two coefficients becomes smaller with increasing collision velocity. The diffusion coefficient was found to depend on collision velocity and angle. It increases linearly with collision velocity when the collision angle is maintained constant at 10° and decreases linearly with collision angle when the collision velocity is maintained constantly at 440 m/s. Based on our MD simulation results and Fick’s second law, a mathematical formula to calculate the thickness of diffusion layer was proposed and its validity was verified by relevant experiments. Transmission electron microscopy and energy-dispersive system were also used to investigate the atomic diffusion behavior at the bonding interface in the explosively welded 6061/AZ31B composite plate. The results show that there were obvious Al and Mg atom diffusion at the bonding interface, and the diffusion of magnesium atoms from magnesium alloy plate to aluminum alloy plate occurs much faster than the diffusion of aluminum atoms to the magnesium alloy plate. These findings from the current study can help to optimize the explosive welding process.

Key words: Al/Mg composite plate, Explosive welding, Molecular dynamics simulation, Atomic diffusion behavior

Ting-Ting Zhang, Wen-Xian Wang, Jun Zhou, Xiao-Qing Cao, Rui-Shan Xie, Yi Wei. Molecular Dynamics Simulations and Experimental Investigations of Atomic Diffusion Behavior at Bonding Interface in an Explosively Welded Al/Mg Alloy Composite Plate[J]. Acta Metallurgica Sinica (English Letters), 2017, 30(10): 983-991.

Figures/Tables 16

Fig. 1 Schematic of Al/Mg composite plate by explosive welding: a explosive welding process; b geometrical analysis

Fig. 2 Initialization configuration for the MD simulation

Table 1 Initial condition parameters in the simulation

No.	β (°)	V_p (m/s)	V_p_x (m/s)	V_p_z (m/s)	V_d (m/s)
1	10	400	34.86	-398.48	2294.74
2	10	410	35.73	-408.44	2352.11
3	10	420	36.61	-418.40	2409.48
4	10	430	37.48	-428.36	2466.85
5	10	440	38.34	-438.33	2524.22
6	10	450	39.22	-428.36	2581.59
7	10	460	40.09	-458.25	2638.95
8	10	470	40.96	-468.21	2696.32
9	10	480	41.83	-478.17	2753.69
10	2	440	7.68	-439.93	12,605.7
11	4	440	15.36	-439.73	6303.82
12	6	440	23.03	-439.40	4203.61
13	8	440	30.69	-438.93	3153.83
14	10	440	38.35	-438.33	2524.22
15	12	440	45.99	-437.59	2104.69

Fig. 3 Temperature and pressure change in system with time during the loading stage when Vp = 440 m/s and β = 10°

Fig. 4 Mean-squared displacement curves in the z-direction during the loading stage and the unloading stage when Vp = 440 m/s, β = 10°

Fig. 5 Diffusion coefficients of Al and Mg at different collision velocities when β = 10°

Fig. 6 Diffusion coefficients of Al and Mg at different collision angles when Vp = 440 m/s

Fig. 7 Configurations of the cross section when β = 10°, Vp = a 400 m/s, b 440 m/s, c 480 m/s at 300 ps after loading stage begins

Fig. 8 Concentrations of Al and Mg atoms along the z-direction when β = 10°, Vp = a 400 m/s, b 440 m/s, c 480 m/s after 1000 ps in loading stage

Fig. 9 Thickness of the interfacial region as a function of time when Vp = 400 m/s, β = 10° in the unloading stage

Table 2 Prediction equations at different velocities when $\beta$ is fixed at 10°

Velocity (m/s)	D_Mg (nm²/ps)	D_Al (nm²/ps)	Fitted equation (nm)	Prediction equation (nm)
400	0.00375	0.00006	$y=0.1183 \sqrt{t}$	$L =\sum\limits_{{i={Mg, Al}}} {1.7149\sqrt {D_{i}t}}$
410	0.00351	0.00071	$y=0.1451t\sqrt{t}$	$L =\sum\limits_{{i={Mg, Al}}} {1.6893\sqrt {D_{i}t}}$
420	0.0039	0.00132	$y=0.1542t\sqrt{t}$	$L =\sum\limits_{{i={Mg, Al}}} {1.5610\sqrt {D_{i}t}}$
430	0.00412	0.00215	$y=0.1644t\sqrt{t}$	$L =\sum\limits_{{i={Mg, Al}}} {1.4870\sqrt {D_{i}t}}$
440	0.00451	0.00278	$y=0.1787t\sqrt{t}$	$L =\sum\limits_{{i={Mg, Al}}} {1.4906\sqrt {D_{i}t}}$
450	0.00454	0.00348	$y=0.1921 \sqrt{t}$	$L =\sum\limits_{{i={Mg, Al}}} {1.5201\sqrt {D_{i}t}}$
460	0.0051	0.00398	$y=0.1922 \sqrt{t}$	$L =\sum\limits_{{i={Mg, Al}}} {1.4810\sqrt {D_{i}t}}$
470	0.00537	0.00468	$y=0.2078 \sqrt{t}$	$L =\sum\limits_{{i={Mg, Al}}} {1.4666\sqrt {D_{i}t}}$
480	0.00581	0.00550	$y=0.2221 \sqrt{t}$	$L =\sum\limits_{{i={Mg, Al}}} {1.4769\sqrt {D_{i}t}}$

Fig. 10 Schematic sketch of an experimental setup for the explosive welding of 6061 Al/AZ31B Mg alloy

Fig. 11 Surface and cross-sectional morphologies of the 6061/AZ31B cladding plate after explosive welding

Fig. 12 SEM micrograph a, EDS line scan b of the AZ31B/6061 composite plate interface after explosive welding

Fig. 13 TEM image of the bonding interface after explosive welding

Fig. 14 EDS testing results of the zone at the interface boxed in Fig. 13

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