Underwater friction stir welding (FSW) on 7A04-T6 aluminum alloy plates was carried out, and the effect of rotation rate on microstructure and mechanical properties of joints was investigated. The results show that the minimum hardness of underwater FSW joints is located in the thermo-mechanically affected zone. The hardness of welded joints at the high rotation rate of 950r/min exhibits W-shaped distribution, and the average hardness value in the nugget zone is higher than that of welded joints at the low rotation rate of 475, 600, 750r/min. When the rotation rate increases from 475r/min to 750r/min with a constant welding speed of 235mm/min, the precipitated phases in the nugget zone gradually become coarse, and the ultimate tensile strength coefficient of the joint decreases from 89.71% to 82.33%; when rotation rate increases to 950r/min, the precipitated phases dissolve into aluminum matrix during welding, and age after welding. This produces the fine and homogeneous dispersed phases, which results in an increase of the strength coefficient to 89.04% and a certain enhancement of strain hardening capacity and elongation for the joints. All the tensile fracture surfaces exhibit the mixed characteristics of microporous polymerization and cleavage fracture.
MISHRA R S , MA Z Y . Friction stir welding and processing[J]. Materials Science and Engineering:R:Reports, 2005, 50 (1): 1- 78.
2
THOMAS W M, NEEDLHAM J C, DAWES C J, et al. Friction stir butt welding:9125978.8[P]. 1991-12-06.
3
WANG W , WANG K S , GUO Q , et al. Effect of friction stir processing on microstructure and mechanical properties of cast AZ31 magnesium alloy[J]. Rare Metal Materials and Engineering, 2012, 41 (9): 1522- 1526.
doi: 10.1016/S1875-5372(13)60004-1
4
WANG K S , WU J L , WANG W , et al. Underwater friction stir welding of ultrafine grained 2017 aluminum alloy[J]. Journal of Central South University, 2012, 19 (8): 2081- 2085.
doi: 10.1007/s11771-012-1248-2
LI J Z , MA Z B , DONG C L , et al. Material flowing behaviors of friction stir welding by dissimilar aluminum alloys[J]. Journal of Materials Engineering, 2014, (6): 1- 4.
doi: 10.11868/j.issn.1001-4381.2014.06.001
WANG C S , XIONG J T , LI J L , et al. Temperature evolution in fatigue test of 2024 aluminum alloy weld fabricated by friction stir welding[J]. Journal of Materials Engineering, 2015, 43 (9): 53- 59.
doi: 10.11868/j.issn.1001-4381.2015.09.009
7
GENEVOIS C , DESCHAMPS A , DENQUIN A , et al. Quantitative investigation of precipitation and mechanical behaviour for AA2024 friction stir welds[J]. Acta Materialia, 2005, 53 (8): 2447- 2458.
doi: 10.1016/j.actamat.2005.02.007
8
SRIVATSAN T S , VASUDEVAN S , PARK L . The tensile deformation and fracture behavior of friction stir welded aluminum alloy 2024[J]. Materials Science and Engineering:A, 2007, 466 (1/2): 235- 245.
9
LI J Q , LIU H J . Characteristics of the reverse dual-rotation friction stir welding conducted on 2219-T6 aluminum alloy[J]. Materials & Design, 2013, 45, 148- 154.
10
SHEN Z K , YANG X Q , ZHANG Z H , et al. Microstructure and failure mechanisms of refill friction stir spot welded 7075-T6 aluminum alloy joints[J]. Materials & Design, 2013, 44, 476- 486.
11
BENAVIDES S , LI Y , MURR L E , et al. Low-temperature friction-stir welding of 2024 aluminum[J]. Scripta Materialia, 1999, 41 (8): 809- 815.
doi: 10.1016/S1359-6462(99)00226-2
12
LIU H J , ZHANG H J , YU L . Effect of welding speed on microstructures and mechanical properties of underwater friction stir welded 2219 aluminum alloy[J]. Materials & Design, 2011, 32 (3): 1548- 1553.
13
ZHANG H J , LIU H J , YU L . Microstructure and mechanical properties as a function of rotation speed in underwater friction stir welded aluminum alloy joints[J]. Materials & Design, 2011, 32 (8/9): 4402- 4407.
14
FRATINI L , BUFFA G , SHIVPURI R . Mechanical and metallurgical effects of in process cooling during friction stir welding of AA7075-T6 butt joints[J]. Acta Materialia, 2010, 58 (6): 2056- 2067.
doi: 10.1016/j.actamat.2009.11.048
15
LIU H J , ZHANG H J , HUANG Y X , et al. Mechanical properties of underwater friction stir welded 2219 aluminum alloy[J]. Transactions of Nonferrous Metals Society of China, 2010, 20 (8): 1387- 1391.
doi: 10.1016/S1003-6326(09)60309-5
XU R Q , WANG W , HAO Y X , et al. Microstructure and mechanical properties of underwater friction stir welded 7A04-T6 aluminum alloy[J]. Journal of Aeronautical Materials, 2015, 35 (4): 16- 21.
doi: 10.11868/j.issn.1005-5053.2015.4.003
17
ZHANG Z M , YU J M , WANG Q , et al. Effects of multiple plastic deformations on microstructure and mechanical properties of 7A04-T6[J]. Rare Metal Materials and Engineering, 2011, 40 (Suppl 3): 69- 72.
18
CHANG C I , DU X H , HUANG J C . Producing nanograined microstructure in Mg-Al-Zn alloy by two-step friction stir processing[J]. Scripta Materialia, 2008, 59 (3): 356- 359.
doi: 10.1016/j.scriptamat.2008.04.003
19
DIERINGA H . Properties of magnesium alloys reinforced with nanoparticles and carbon nanotubes:a review[J]. Journal of Materials Science, 2011, 46 (2): 289- 306.
doi: 10.1007/s10853-010-5010-6