Investigation on oscillating laser welding of medium thick QAl9-4 aluminum bronze: Weld formation, microstructure and mechanical properties

Oscillating laser welding was successfully employed to weld 8 mm thick QAl9-4 aluminum bronze with butt configuration. The oscillating laser welding technology demonstrates advantages in suppressing typical defects such as porosity and melt pool collapse for welding copper alloys with medium thickness. The results indicated that the laser beam oscillation effectively improved the weld formation and promoted the grain refinement in the fusion zone due to the high frequency stirring and mixing effect. The rapid cooling rate resulted in the formation of fine equiaxed grain structures and κ phase precipitates in the fusion zone. However, significant differences in temperature gradients and cooling rates between the upper and lower region of the weld led to distinct microstructural and performance variations in the upper and lower fusion zone. The upper fusion zone showed finer grains and the higher fraction of κ precipitates that those in the lower fusion zone, which resulted in higher microhardness in the upper fusion zone compared to the lower fusion zone. The tensile properties of the welded specimens were comparable to those of the base material with failure occurring in the base material away from the weld, and they exhibited an increased yield strength compared to the base material. These findings provide valuable insights for welding medium thick copper alloys with high performance.