With the increasing demands for national defense, NiTi shape memory alloy (SMA) and 5052 aluminum alloy have become a significant research focus. This study addressed cracking, porosity, intermetallic compound (IMC) formation, and degradation of the shape memory effect during laser lap welding of NiTi SMA and 5052 aluminum alloy. Systematic investigations were conducted on process optimization, microstructural characterization, and mechanical property evaluation. The results demonstrate that welding heat input critically regulates both weld morphology and the thickness of the interfacial reaction layer. With increasing heat input, the reaction layer composed of Ti–Al IMCs gradually thickens, which significantly alters the solidification behavior and mechanical response of the joint. Microstructural analysis reveals a clear transition from columnar or cellular structures near the fusion line to equiaxed dendritic structures in the weld center, governed by variations in thermal gradient and solidification rate. Mechanical testing indicates that joint failure consistently occurs within the weld zone and is dominated by cleavage fracture. The formation of brittle Ti–Al IMCs is identified as the fundamental origin of crack initiation and propagation, as evidenced by river patterns and cleavage facets on the fracture surfaces. Under optimized thermal conditions, a balance between sufficient penetration and suppressed interfacial reaction can be achieved, resulting in a maximum tensile strength of 256.22 MPa. Differential scanning calorimetry (DSC) analysis further reveals that the welding thermal cycle induces a shift of phase transformation temperatures and a reduction in transformation enthalpy of the NiTi SMA. The combined effects of element redistribution, residual stress, and reduced NiTi phase fraction lead to degradation of shape memory functionality in the weld metal region. This work elucidates the intrinsic heat input–microstructure–fracture mechanism governing NiTi/Al laser-welded joints and informs joining strategies for other advanced functional material systems, such as thermoelectric interfaces.
Zhang et al. (Sun,) studied this question.