Abstract
Resistance spot welding of aluminum (Al5754) to magnesium (AZ31B) alloys results in the formation of a variety of solidification microstructures and intermetallic compounds that may affect the in-service performance of the weld. This study evaluates the relationship between the welding parameters and the properties of the weld nugget that is formed, and clarifies the morphological and microstructural evolutions within the weld regions during the low-current “small-scale” resistance spot welding of Al5754 to AZ31B. The investigations included a combination of microstructural characterization and thermodynamic analysis of the weld region. The results show that the welding time and clamping force parameters have significant effects on the properties of the nugget formed. The optimal welding parameters were found to be 300 ms welding time and 800 N clamping force. Weld nuggets formed with lower welding time and clamping force were undersized and contained extensive porosity. Meanwhile, a clamping force above 800 N caused gross deformation of the test samples and the expulsion of the molten metal during the welding process. The most significant microstructural changes occurred at the weld/base metal interfaces due to the formation of Al17Mg12 and MgAl2O4 intermetallic compounds as well as significant compositional variation across the weld pool. The thermal gradient across the weld pool facilitated the formation of several microstructural transitions between equiaxed and columnar dendrites.
Highlights
The dissimilar joining of advanced alloys and composites to form hybrid structures has become desirable as a way of reducing energy consumption and improving fuel efficiency when designing engineering systems [1,2]
Various techniques have been used for joining dissimilar metals, such as metal inert gas welding (MIG) or tungsten inert gas welding (TIG), Shahid et al [8] demonstrated that the primary limitation encountered during the fusion welding process is the formation of intermetallic compounds within the weld zone, which compromises the strength of the weld
The optimized weld nugget was characterized for its composition, morphology, microstructure, and solidification sequence
Summary
The dissimilar joining of advanced alloys and composites to form hybrid structures has become desirable as a way of reducing energy consumption and improving fuel efficiency when designing engineering systems [1,2]. Various techniques have been used for joining dissimilar metals, such as metal inert gas welding (MIG) or tungsten inert gas welding (TIG), Shahid et al [8] demonstrated that the primary limitation encountered during the fusion welding process is the formation of intermetallic compounds within the weld zone, which compromises the strength of the weld. These compounds form because of high welding temperatures causing heterogeneous compositional variations across the weld region, which lead to the precipitation of intermetallic phases that decrease the joint strength. Friction stir spot welding has shown progress in joining Al to Mg alloys, as found by [10] and [11]
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