Abstract
In this study, friction stir welding of AA2014-O and AA2014-T6 aluminum alloy was performed at various welding speeds to evaluate the influence of temper conditions of base metal (BM) on the properties of the welded joints. The results showed strong influence of BM temper conditions on the microstructural morphologies and mechanical behavior of the welded joints. In the 2014-O joints, different zones of weld joint were diffused into each other and there was no clear interface between them. In 2014-T6 joints, there was a distinct demarcation between the nugget zone (NZ), thermomechanically affected zone TMAZ, heat-affected zone (HAZ), and BM. The welded joints in 2014-O temper condition showed increase in hardness in the vicinity of weld center due to grain refinement whereas, in 2014-T6, softening occurred in the same region by the dissolution of strengthening precipitates. The mechanical properties of 2014-O joints were equivalent to the base metal showing a 100% weld efficiency with fracture located in the base metal, whereas 2014-T6 welds exhibited about 70% weld efficiency with fracture located at the NZ/TMAZ interface. All the samples in mechanical testing fractured at retreating side (RS) which exhibited heterogeneity in the mechanical properties of the welded joints. Scanning electron microscopy fractographic analysis revealed a ductile fracture mode comprising of dimples in both temper conditions. The size and shape of the dimples were strongly dependent on base metal temper condition.
Highlights
The heat treatable aluminum alloys of 2xxx series are the key alloys used in structures where the key design benchmark is high specific strength, good fracture toughness and damage tolerance such as aerospace, marine, petrochemical, power generation and transport industries [1,2,3,4]
The typical four regions of the friction stir welded joint are labeled as nugget zone (NZ), thermomechanically affected zone (TMAZ), heat affected zone (HAZ) and base metal (BM)
Following conclusions can be drawn from the analysis of results of the friction stir welded 2014 alloy in different heat treatment conditions: The microstructural morphologies of the friction stir welded joints of AA2014 strongly depend on BM temper conditions
Summary
The heat treatable aluminum alloys of 2xxx series are the key alloys used in structures where the key design benchmark is high specific strength, good fracture toughness and damage tolerance such as aerospace, marine, petrochemical, power generation and transport industries [1,2,3,4]. Material flow behavior in the welds has been addressed by many researchers such as Huaxia et al [20] studied the material flow behavior of friction stir welded 2024-T351 with the help of thin copper strips They observed that at different welding parameters the material fragmentation and dispersion is decreased at high heat inputs and vice versa. The research work related to friction stir welding of AA 2014 alloy is mostly focused on T6-tempered condition and the comparative studies of weld characteristics and joint performance in different heat treatment conditions of base metal are not available. AA2014 aluminum alloy sheets were friction stir welded in two different heat treatment states i.e. annealed ‘O’ and age-hardened ‘T6’ conditions to evaluate the influence of different temper conditions of the base metal on microstructural morphologies, strength and fracture characteristics. A comprehensive assessment of microstructural development, strength and hardness in the weld zone of the joints is made between the ‘O’ and ‘T6’ temper conditions
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