Effect of Ultrasound on Heterogeneous Nucleation in TIG Welding of Al-Li Alloy

doi:10.1007/s40195-016-0483-1

Abstract

Abstract:

The effect of ultrasound on heterogeneous nucleation in a tungsten inert gas (TIG) weld pool of 2195 Al-Li alloy has been investigated by a series of experiments. An ultrasonic vibration was imposed on the surface of base material before turning off the welding arc during the TIG welding implemented at a fixed point. The results suggest that ultrasound could promote heterogeneous nucleation in the TIG weld pool of 2195 Al-Li alloy. The grain around the fusion zone is changed from a column grain to an equiaxed grain after applying the ultrasonic treatment. To study the influencing mechanism of ultrasound on heterogeneous nucleation, further investigations were implemented where the welding arc was turned off after turning off the ultrasonic power. The results show that the equiaxed grain around the fusion zone disappeared gradually with an increase in heat input after turning off the ultrasonic power. It suggests that ultrasound could promote the heterogeneous nucleation particle to nucleate in advance before turning off the welding arc and the crystal nucleus could again be melted with an increase in heat input after turning off the ultrasonic power. Moreover, the effects of the welding current and ultrasonic amplitude on heterogeneous nucleation in the weld pool of 2195 Al-Li alloy were also investigated. Possible influencing mechanism of the welding current and ultrasonic amplitude on heterogeneous nucleation was discussed.

Key words: Ultrasound, TIG welding, Grain, Al-Li alloy

Qi-Hao Chen,San-Bao Lin,Chun-Li Yang,Cheng-Lei Fan,Hong-Liang Ge. Effect of Ultrasound on Heterogeneous Nucleation in TIG Welding of Al-Li Alloy[J]. Acta Metallurgica Sinica (English Letters), 2016, 29(12): 1081-1088.

Figures/Tables 12

Table 1 Chemical composition of the studied materials (wt%)

Material	Li	Ag	Si	Fe	Cu	Ti	Zr	Al
2195	1.00	0.40	0.03	0.16	4.02	0.068	0.11	Bal.
1A99	-	-	0.003	0.003	0.005	-	-	Bal.

Fig. 1 Schematic illustration of the experimental setup

Table 2 Experimental parameters in TIG welding with different welding time

Experimental number	Welding current (A)	Ultrasonic amplitude (μm)	Turn-off time of welding power (s)
S-1	66	7.2	17
S-2	66	7.2	21
S-3	66	7.2	25
S-4	66	7.2	29

Table 3 Experimental parameters in TIG welding with different welding currents

Experimental number	Welding current (A)		Ultrasonic amplitude (μm)
Experimental number	0-17 s	17-22 s	Ultrasonic amplitude (μm)
S-5	60	60	7.2
S-6	60	70	7.2
S-7	60	75	7.2

Table 4 Experimental parameters about the effect of welding current and welding time on heterogeneous nucleation

Experimental parameter	Experimental number
Experimental parameter	1	2	3	4	5	6	7	8
Welding current (A)	40	50	60	70	70	70	70	70
Ultrasonic amplitude (μm)	7.2	7.2	7.2	7.2	0	8.4	8.8	11.4

Fig. 2 Microstructures around the fusion zone of 2195 Al-Li alloy a, b and 1A99 Al alloy c, d: a, c without ultrasound; b, d with ultrasound

Fig. 3 Equiaxed grain size around the fusion zone for the 2195 Al-Li alloy with different arc delay time

Fig. 4 Microstructure around the fusion zone for the 2195 Al-Li alloy with different welding currents a 60A, b 70A, c 75A

Fig. 5 Relation between the equiaxed grain size around the fusion zone of Al-Li alloy and the heat input

Fig. 6 a Relation between the maximum pressure and the acoustic pressure; b relation between the freezing temperature and the cavitation pressure

Fig. 7 Schematic diagram of the heterogeneous nucleation in the TIG weld pool of the 2195 Al-Li alloy with ultrasound

Fig. 8 Equiaxed grain size around the fusion zone of the 2195 Al-Li alloy: a with different welding currents; b with different ultrasonic amplitudes

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