Pulse-duration-governed interfacial evolution in non-optical-contact ultrashort-pulse laser micro-welding of glass-to-aluminum alloy joints

Direct joining of high-aluminosilicate glass with 6061 aluminum alloy is important for compact microelectronic and optoelectronic packages, but remains challenging because of their pronounced thermophysical mismatch and the micrometer-scale interfacial gap present under non-optical-contact conditions. In this paper, 1-mm-thick high-aluminosilicate glass and 1-mm-thick 6061 aluminum alloy were joined without external clamping using a 1030 nm ultrashort-pulse laser, with emphasis on the influence of pulse duration on energy deposition, interfacial evolution, defect formation, and mechanical performance. The pulse-duration series covered 300–4000 fs at a fixed repetition frequency of 0.4 MHz in two-pulse burst mode; pulse energy, focal position, repetition frequency, and welding speed were evaluated separately in the process-optimization experiments. Continuous joints were obtained over 300–3000 fs, but isolated microcracks appeared from 1200 fs and became more pronounced at 2000–3000 fs, whereas 4000 fs produced severe heat-affected-zone expansion, interfacial pores, and crack coalescence. SEM, EDS, and fracture-surface observations show that the initial 60 ± 5 μm gap was progressively bridged by localized interfacial melting, plasma-assisted material redistribution, and rapid resolidification. The characteristic weld-zone width increased from approximately 70.1 μm at 300 fs to about 150 μm in the 1–3 ps regime, demonstrating a transition from strongly localized energy deposition toward increasing thermal accumulation. Separate mechanical-parameter experiments yielded a maximum nominal shear strength of 8.79 MPa at 14 μJ pulse energy, zero defocus, 400 kHz repetition frequency, and 0.2 mm/s welding speed. These findings identify pulse duration as a key control parameter for balancing nonlinear energy localization and thermal accumulation in glass-metal ultrashort-pulse laser welding. This work provides fundamental insight into the process-structure-property relationship of non-optical-contact glass-aluminum joining and offers a practical strategy for integrating lightweight dissimilar materials in high-reliability microelectronic and optoelectronic devices.