Mechanical and Fatigue Strength Assessment of Friction Stir Welded Plates of Magnesium Alloy AZ31B

Luna, Carlos Fernando; Arenas, Fernando Franco; Pereira, Victor Ferrinho; Ávila, Julián Arnaldo

doi:10.1590/0104-9224/SI2301.06

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Technical Papers • Soldag. insp. 23 (1) • Jan-Mar 2018 • https://doi.org/10.1590/0104-9224/SI2301.06 copy

Mechanical and Fatigue Strength Assessment of Friction Stir Welded Plates of Magnesium Alloy AZ31B

Avaliação da Resistência Mecânica e à Fadiga de Chapas Soldadas por Atrito com Pino não Consumível da Liga de Magnésio AZ31B

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Light-alloys play a significant role in saving weight in automotive and aerospace industries; however, a few joining methods guarantee mechanical and fatigue strengths for high performance application. Even conventional arc welding processes do not offer constant quality joints. Therefore, this study uses an alternative solid-state welding process, friction stir welding (FSW), to analyze post processing microstructures and assess mechanical and fatigue strength. Magnesium alloy AZ31B plates were welded using different welding parameters in a dedicated FSW machine. The effect of the spindle speed (ω) and welding speed (ν) on the microstructure, the tensile strength and fatigue were studied. The stirred zone (SZ) at the FS-welded joints presented a microstructure composed by homogeneous equiaxial grains, refined by dynamic recrystallization. A rise in grain size, weld bead width, tensile and fatigue strengths with the increase of speed ratio (ω/ν) were observed. Results of the fatigue and mechanical strength here presented outperformed results from welds made with conventional milling machines.

Key-words:
Magnesium AZ31B; Fatigue strength; Tensile strength; Friction stir welding; FSW

ω (rpm)	ν (mm/min)
ω (rpm)	100	200	300
1200	12	6	4.0
1600	16	8	5.3
2000	20	10	6.7

Mg alloy	Al	Mg	Fe	Mn	Si	Zn
AZ31B	2.8	Bal	0.007	0.52	0.09	1.0

ω	ν	ω /ν	ω²/ν	Grain size	Grain size	Bead width	T_max
(rev min^-1)	(mm min^-1)	(rev/mm)	(rev²/ mm)	No. ASTM [ ¹⁰10 ASTM International. ASTM E112-13 Standard Test Methods for Determining Average Grain Size. West Conshohocken: ASTM International, 2013. http://dx.doi.org/10.1520/E0112. http://dx.doi.org/10.1520/E0112 ... ]	(μm)	(mm)	(°C)
1200	100	12	14400	11.52	6.84	5.9	463
	200	6	7200	11.88	6.00	5.4	448
	300	4	4800	12.00	5.60	5.3	439
1600	100	16	25600	9.88	11.70	6.9	477
	200	8	12800	10.53	9.31	6.5	461
	300	5	8533	10.54	9.28	6.5	451
2000	100	20	40000	9.38	13.92	7.6	488
	200	10	20000	9.95	11.41	7.3	471
	300	7	13333	10.08	10.91	7.2	462
Base Material				5.10	61.50	---	---

Specimen	A	m	Fatigue strength (MPa), 2x10⁶ cycles	Test to failure	Run out tests (No failure)	Standard deviation of log N
FSW (This study)	22.43	-8.77	69.00	16.00	0.00	0.60
BM (ref. [ ¹1 Avila JAD, Jaramillo HE, Franco AF. Fatigue of friction stir and GTAW welded AZ31B magnesium alloy. In: American Society of Mechanical Engineers. ASME 31 International Conference on Offshore Mechanics & Arctic Engineering; Rio de Janeiro. Rio de Janeiro: ASME; 2012. p. 365-370. ])	20.25	-7.83	81.00	19.00	2.00	0.52
FSW (ref. [ ¹1 Avila JAD, Jaramillo HE, Franco AF. Fatigue of friction stir and GTAW welded AZ31B magnesium alloy. In: American Society of Mechanical Engineers. ASME 31 International Conference on Offshore Mechanics & Arctic Engineering; Rio de Janeiro. Rio de Janeiro: ASME; 2012. p. 365-370. ])	19.08	-7.80	60.00	14.00	0.00	0.57
GTAW (ref. [ ¹1 Avila JAD, Jaramillo HE, Franco AF. Fatigue of friction stir and GTAW welded AZ31B magnesium alloy. In: American Society of Mechanical Engineers. ASME 31 International Conference on Offshore Mechanics & Arctic Engineering; Rio de Janeiro. Rio de Janeiro: ASME; 2012. p. 365-370. ])	13.85	-5.20	48.00	16.00	0.00	0.61
BM (ref. [ ⁹9 Padmanaban G, Balasubramanian V. Fatigue performance of pulsed current gas tungsten arc, friction stir and laser beam welded AZ31B magnesium alloy joints. Materials & Design. 2010;31(8):3724-3732. http://dx.doi.org/10.1016/j.matdes.2010.03.013. http://dx.doi.org/10.1016/j.matdes.2010... ])	10.36	-2.80	72.00	5.00	---	0.56
FSW (ref. [ ⁹9 Padmanaban G, Balasubramanian V. Fatigue performance of pulsed current gas tungsten arc, friction stir and laser beam welded AZ31B magnesium alloy joints. Materials & Design. 2010;31(8):3724-3732. http://dx.doi.org/10.1016/j.matdes.2010.03.013. http://dx.doi.org/10.1016/j.matdes.2010... ])	9.35	-2.40	40.00	5.00	---	0.48
GTAW (ref. [ ⁹9 Padmanaban G, Balasubramanian V. Fatigue performance of pulsed current gas tungsten arc, friction stir and laser beam welded AZ31B magnesium alloy joints. Materials & Design. 2010;31(8):3724-3732. http://dx.doi.org/10.1016/j.matdes.2010.03.013. http://dx.doi.org/10.1016/j.matdes.2010... ])	9.07	-2.33	49.00	5.00	---	0.46

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