EBSD characterization of CuZn alloys welded by using fiber laser

Brass alloys are widely used as engineering materials in several industrial applications, thanks to their high strength, high corrosion resistance, and high electrical and thermal conductivity. For the brass, the conventional fusion welding shows some obvious limitations. Some of the main problems of these alloys during their welding is the evaporation of the zinc and the difficulties of obtaining crack free beads. The laser welding can offers some advantages, such as the productivity, limited heat flow and minor thermal damages. In particular, the diffusion of high power fiber lasers in manufacturing has solved some problems when high reflectivity alloys, like copper and its alloys, can be characterized when machined by using a laser beam. In this study, the welding process was realized by using 1 kW continuous wave fiber laser on commercial brass. Bead on plate and lap joint configurations were taken into account during the joining test on both bulk and cellular material; the beads were performed at varying the welding speed. Cross sections of the beads were prepared in order to analyze the microstructure in different areas: fusion zone, heat affected zone and base material. It was seen that the joints were realized in keyhole modality, thanks to the high irradiance of the laser beam. Optical microscopy revealed that different microstructures forms not only in the different materials, but also inside the same bead. Main reasons could be chemical inhomogeneity or different thermal histories, due to strong convective circulation of liquid metal inside the melted pool. On the contrary, no evident effect of the welding speed on the microstructure was detected on the joints investigated. In order to identify the reason of such differences, compositional analysis was done across the welded bead, to detect modifications of the element content. EBSD investigation was performed in the same areas of the samples, to identify the phases and orientation relationship in the microstructurally different areas. Element segregation inside the welding pool was detected, and also phase content in the different microstructures could be determined. Work is in progress in order to correlate phase content to chemical composition and thermal histories in the different areas of the welded joint.