Effect of pulsed laser frequency on microstructure and mechanical properties of 2219 aluminum alloy welded joints

As an excellent lightweight alloy, 2219 aluminum alloy is widely used in structural parts of aerospace equipment. Pulsed laser is used for welding 2219 aluminum alloy sheets in this research. A welded joint with good macroscopic morphology, high mechanical properties, and little thermal deformation is obtained. The large chain-like Cu segregates as alpha-Al + Al2Cu eutectics at the grain boundary. Increased pulse frequency gradually improved the macro-morphology of the weld, and micro-segregation of Cu in the weld zone weakened. There is basically no preferred orientation for grain growth in the weld zone. Under the influence of welding heat input, the original strengthened phases theta" and theta' in the weld zone are transformed into theta phases. The orientation relationship between the theta phase and the matrix can be described as [11 0]theta//[2 0 0]alpha in the heat-affected zone. The tensile strength of welded tensile specimens gradually increases with an increase in pulse frequency. When the pulse frequency is 27 Hz, the ultimate tensile strength can reach 270.3 +/- 0.9 MPa, approximately 69 % of the base metal strength. The fracture mode of welded joint is a quasi-cleavage fracture including brittle fracture and ductile fracture.