In situ monitoring of Cu/Al laser welding using Laser Induced Fluorescence
Brian J. Simonds, Bao Tran, Paul Williams
Abstract
Laser-induced fluorescence (LIF) is used to investigate laser spot welding of 200 µm thick Cu and Al foils. The key to strong Cu/Al welds is limited intermetallic compound formation through controlled molten metal interaction time. For laser lap welds, Cu in the vapor plume is indicative of the degree of Cu melting. LIF sensitively detects individual elements and is used to interrogate the vapor plume for the earliest presence of Cu atoms. We perform welds across a wide range of laser power (3 kW – 8 kW) for a pulse duration of 2 ms. We qualitatively determine weld strength by mechanically pulling apart the samples. Temporally resolved LIF signals, along with backscattered laser light monitoring, demonstrate Cu detection immediately upon Al penetration. We find that LIF can detect Cu even under laser power conditions too weak to create a strong weld, which suggests that LIF may be sensitive enough for real-time, in situ monitoring of Cu/Al laser welding.