W. Aman
S. Nothdurft
J. Hermsdorf
S. Kaierle
L. Overmeyer

Surface deoxidation of aluminium alloys with ns-pulsed laser radiation in XHV-adequate atmosphere for laser brazing processes

International Congress on Applications of Lasers & Electro-Optics (ICALEO)
18.-20. Oktober
Type: Konferenzbeitrag
Laser beam brazing is an established manufacturing process, due to its low heat input and aesthetically appealing joints. However, brazing of materials with a high oxygen affinity, such as aluminium alloys, requires the removal of the surface oxides prior to the brazing process, commonly through the application of chemical fluxes that may be harmful to environment and health. The approach presented dispenses with the use of fluxes and involves oxide layer removal by means of ns-pulsed laser radiation within an XHV-adequate atmosphere. By doping the process gas with monosilane (SiH4), an oxygen content equivalent to an ultra-high vacuum of 10-23 bar is realized. Hence, a subsequent reoxidation is actively prevented, so that wetting of the base material by the solder and consequent diffusion processes are enabled. Images of the material surface after pulsed laser irradiation, taken with a confocal microscope, show that the material is only moderately affected, which indicates that no significant negative effects are to be expected for the brazed joint. This assumption is supported by corresponding cross sections of the treated surface. The wetting angle between solder and material is used to evaluate the effectiveness of laser-based deoxidation under XHV-adequate atmosphere. The results achieved with regard to the wetting angle, where values below 30° can be considered to be ideal, are compared with experiments under conventional argon atmosphere. Thus, it can be shown that even the low residual oxygen content of the argon atmosphere is sufficient to prevent an effective brazing process.