AbstractUp to date the evaporation process in laser beam welding of alloys with volatile elements is not completely understood. This paper discusses the phenomena occurring at the welding process of brass with 37m% zinc. Since copper has a solidification temperature of 1,087°C and zinc vaporizes at a temperature of 907°C, a strong evaporation takes place and anelongation of the keyhole can be observed. Depending upon welding velocity, the ratio of keyhole length to width is between one and six. Furthermore it is observed that a defect free weld seam is formed. Since the melt pool does not leak also for high ratios of keyhole length to width, the conventional keyhole model with a dynamic flow around the laser beam has to be adapted to a model in which the melt flow at the side of the capillary is stabilized also outside of the interaction zone of the laser beam with the melt due to strong evaporation at the flank of the keyhole.