LASER ASSISTED JOINING OF DISSIMILAR MATERIALS Gerhard LIEDL, Alexander KRATKY, Matthias MAYR, Alexandra SALIGER Institute for Production Engineering and High Power Laser Technology, Vienna University of Technology, Gusshausstrasse 30, 1040 Vienna, Austria E-mail: gerhard.liedl@tuwien.ac.at ABSTRACT Joining of dissimilar materials is often challenging due to different material properties. Laser welding is an attractive technique compared to conventional joining techniques of dissimilar metals since processing speed and precision are high whereas heat input is very low. Laser assisted joining of dissimilar materials, like aluminum alloys – steel, aluminum alloys – titanium and hard metals – steel has been examined with high power Nd:YAG and diode lasers. Joining of aluminum alloys from 5XXX and 6XXX groups (AlMg3 and AlMgSi1) and titanium or micro alloyed steel H340 (galvanized and non-galvanized) have been investigated. Additionally, butt joints between hard metals K40 (86% tungsten carbide, 12 % cobalt and 2% titanium and tantalum carbide) and carbon steel C75 (tensile strength 1450 N/mm 2 ) have been examined. A 1 kW diode laser as well as 3 kW Nd:YAG laser have been used for experiments. Microstructure and mechanical properties of laser welded samples have been investigated by microscopy, SEM and micro hardness analysis. Aluminum – steel samples have been tested by shear strength measurements, too. All aluminum samples have been welded in an overlap configuration. Additionally, aluminum – steel and hard metal - steel samples have been welded in a butt joint configuration. Mismatch of thermo-mechanical properties, like thermal expansion coefficient or thermal conductivities of materials selected for welding and the formation of brittle intermetallic phases result in residual stress formation. Line energy, focal position, shielding gas and laser pre- and post-heating have been varied. A precise temperature control with pre-heat and post-heat treatment has been used to minimize stress and possible weld defects. Results indicate that laser welding produces competitive joints without cracks or pores in the weld seam between dissimilar metals. Keywords: Laser Welding, IMP, Aluminum, Titanium, Hard Metal. 1. INTRODUCTION During the last years the regulatory framework due to economical as well as ecological changes caused an increasing interest on weight and production cost reduction in industry. Customized components with well defined, tailor-made properties assembled from different materials offer new possibilities in weight reduction and functionality. Many different joining methods, like riveting, bonding and others with their pros and cons are in use to join such components of unequal composition. Unfortunately, thermal joining of dissimilar metals tends to the formation of brittle intermetallic phases which narrows possible fields of applications significantly. Generally speaking, growth of unwanted intermetallic compound layers depends on the amount and duration of heat input. Laser assisted joining with its well defined and precise localized energy input offers the possibility to control growth of intermetallic compound layers to a wide extent. 22 _______________________________________________________________________________________________________ IQCMEA-ICF-Processing, Performance and Failure Analysis of Engineering Materials, 14-17 Nov., 2011, Luxor, Egypt