ORIGINAL ARTICLE Laser micro-welding of aluminum alloys: experimental studies and numerical modeling Magnus Rohde & Christine Markert & Wilhelm Pfleging Received: 17 July 2009 / Accepted: 28 December 2009 / Published online: 2 February 2010 # Springer-Verlag London Limited 2010 AbstractExperimental and numerical studieswere con- ducted on the effects of the laser beam pulse shaping in the time domain on the quality of the welding seam in laser micro-welded AlMg3 with a thickness of 0.2 mm and 1 mm thick AlMg4.5 Mg foils, respectively. The pulse shaping was realizedby a time sequenceof threedifferent rectangular pulses with different duration and power level. The firstpulse was used to pre-heat the sample, welding occurredwith the secondpulseand the third pulse controlled the melt pool behavior. The powerleveland the duration of the single pulses were varied systematically and the resulting microstructure was analyzed by scanning electron microscope. The experiments were accompanied by numerical simulations based on a finite volume model which considers the transient heatflow,meltconvection and theevolution ofa gascapillary during thedeep penetration welding process. Keywords Welding . Pulse shaping . Aluminum alloys . Simulation 1 Introduction Two process strategies in laser welding are well established: laser deeppenetrationweldingand laser conduction welding.Forhigh laserpowerdensities (>10 6 W/cm 2 ), a plasma and a so-called keyhole is formed which enables a large aspect ratio of the weld seam and can be used for deep penetration welding [1]. However, generally the volume of the weld seam is too large for applications in microsystem technology.Furthermore, the dynamicof the laser- generated melt can lead to a significant contamination of the surrounding material by melt ejection.Conduction welding is performed at lower laserpowerintensities (<10 6 W/cm 2 ). The widths ofthe weld seams are in the range of 100-300 µm. The depths of the weld seams are o the same order. Because of the highly localized thermal impact, the conduction mode is more appropriate for micr packaging applications. However, the aspect ratio ofthe weld seams, which can be achieved by conduction welding might not be sufficient for every application. In chemical reaction technologies [2], the demand of improved channel devices such as heat-exchangers, mixe and reactors madeof chemically stable materialswith structural detailsin micrometerangeincreases. Laser micro-welding is of most interest if conventional welding technologies such as diffusion bonding or electron-beam welding cannot be applied anymore. This is the case for special materials such as aluminum alloys, tantalum, and high alloyed steel materials. Laser welding of materials with high affinity concerning oxidation and pore and crack formation [ 3] is still a great challenge in microsystem technology. Another challenge i to combine the main advantage of heat conduction weldin (smallheateffected zone) with theadvantage of deep penetration welding (aspect ratio of weld seam >1). In ord to overcome this limitation, a new technical approach uses temporal laser pulse shaping. The first pulse is used in ord to overcome the high reflectivity and high heat conduction of the material.When a melt phaseis formed,the reflectivity is reduced significantly and a second laser puls can be absorbed with high efficiency. Therefore, the weld penetration depth can significantly increased up to aspect M. Rohde (*) : C. Markert : W. Pfleging Forschungszentrum Karlsruhe GmbH, Institute for Materials Research I, Karlsruhe, Germany e-mail: magnus.rohde@kit.edu URL: www.kit.edu Int J Adv Manuf Technol (2010) 50:207–215 DOI 10.1007/s00170-009-2510-0