Microstructural evolution and mechanical behavior of EN AW-2014A (AlCu 4 SiMg)/SiC reinforced composites under friction stir welding

Friction stir welding (FSW) was used to join stir-cast EN AW-2014A aluminum matrix composites reinforced with 5, 10, and 15 wt.% SiC, under fixed process parameters (270 r/min, 78 mm/min, 2° tilt). This work provides the first systematic, zone-resolved analysis linking SiC weight fraction to material flow, weld-zone microstructural evolution, hardness distribution, tensile behavior, and fracture response in FSW of EN AW-2014A composites, establishing an integrated structure–property–process relationship across reinforcement levels. Microstructural evolution across the heat-affected zone (HAZ), thermo-mechanically affected zone (TMAZ), and weld nugget was characterized by optical and scanning electron microscopy and correlated with microhardness and tensile properties. Welds were macroscopically free of gross defects, though microscale voids, particle-free regions, and SiC clustering were observed, increasing with reinforcement content. The 10 wt.% composite produced the most uniform nugget, with a fine, equiaxed grain structure suggestive of dynamic recrystallization and uniform SiC dispersion; 5 wt.% showed limited particle breakup, while 15 wt.% showed agglomeration and voids from high flow resistance. Nugget microhardness rose substantially over the as-cast condition: 95.16 to 127.20 HV, 123.68 to 140.12 HV, and 133.36 to 150.19 HV for 5, 10, and 15 wt.%, respectively (approximately 34%, 13%, and 13% improvement). The HAZ was consistently the softest zone, likely associated with precipitate coarsening/overaging and inherited porosity. Welding reduced tensile strength relative to the as-cast state by 31.16%, 22.90%, and 18.85% for 5, 10, and 15 wt.%, respectively; fracture always occurred in the HAZ or adjacent base metal, never in the nugget. The 15 wt.% composite showed the highest joint efficiency (81.4%), while the 10 wt.% composite retained the highest absolute welded strength and the best overall microstructural homogeneity. Overall, 10 wt.% SiC offers the best balance of weldability, microstructural refinement, and mechanical performance for FSW of EN AW-2014A-based MMCs.