1 State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi'an 710072, China 2 Shaanxi Key Laboratory of Friction Welding Technology, Northwestern Polytechnical University, Xi'an 710072, China 3 Chinese Aircraft Strength Research Institute, Xi'an 710065, China
The weld joints were fabricated by friction stir welding (FSW) on 8mm thick 2024-O aluminum alloy with a rotating speed of 300r/min and a welding speed of 60mm/min. The microstructure and mechanical properties of parent material and weld joints were investigated. The fatigue tests were conducted on both parent metal and weld joint, during which the surface temperatures were recorded by an infrared thermal imager. The results show that the welds exhibit high gradient inhomogeneity in microstructure, and have good fatigue properties. The thermal mechanical affected zone (TMAZ) in advancing side is the weak area as examined by the tensile tests. The temperature change of the specimen surface of the parent material meets the characteristic of "three stages". Surface temperature variation tendency of the FSW welds is the same with that of the parent material in the first stage and the third stage, but has a downward trend in the second stage. The grains of the weld nugget zone and TMAZ accumulate lots of elastic and plastic strain energy through cyclic softening in the second stage that depress the conversion rate of mechanical energy to thermal energy.
WANG Xi-jing, XU Cheng, ZHANG Jie, et al Fatigue life prediction of friction-stir welding joints of aluminum alloy 7070-T651 based on BP algorithm of neural network[J]. Journal of Lanzhou University of Technology, 2008, 34 (3): 12- 15.
ZHANG L, LIU X S, WU S H, et al Rapid determination of fatigue life based on temperature evolution[J]. International Journal of Fatigue, 2013, 54, 1- 6.
LUONG M P Fatigue limit evaluation of metals using an infrared thermographic technique[J]. Mechanics of Materials, 1998, 28 (1): 155- 163.
La ROSA G, RISITANO A Thermographic methodology for rapid determination of the fatigue limit of materials and mechanical components[J]. International Journal of Fatigue, 2000, 22 (1): 65- 73.
LUONG M P Infrared thermographic scanning of fatigue in metals[J]. Nuclear Engineering and Design, 1995, 158 (2-3): 363- 376.
WAGNER D, RANC N, BATHIAS C, et al Fatigue crack initiation detection by an infrared thermography method[J]. Fatigue & Fracture of Engineering Materials & Structures, 2010, 33 (1): 12- 21.
ZHANG H X, WU G H, YAN Z F, et al An experimental analysis of fatigue behavior of AZ31B magnesium alloy welded joint based on infrared thermography[J]. Materials & Design, 2014, 55, 785- 791.
YAO Lei-jiang, LI Bin, TONG Xiao-yan Experimental study of the correlation between energy dissipation and surface microstructure evolution during fatigue[J]. Journal of Northwestern Polytechnical University, 2008, 26 (2): 225- 228.