Author(s): Martins, Jorge Miguel Ribeiro
Date: 2013
Persistent ID: http://hdl.handle.net/10362/10723
Origin: Repositório Institucional da UNL
Subject(s): Friction stir welding; Diffusion process; Copper; Stainless steel; Dissimilar joint; Mechanical resistance
Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do Grau de Mestre em Engenharia Mecânica
One of the major trends in welding and joining technology is to join dissimilar materials taking advantage of individual materials properties. Among these, copper to stainless steel joining has significant industrial applications and importance where e.g. the highest electrical and thermal conductivities are required to engineering materials associated to good corrosion resistance. However, joining these materials is difficult due to their very different chemical composition and thermo-physical properties. Additionally, they easily form intermetallic phases that deteriorate the mechanical strength of the joint. Thus investigating the feasibility of applying alternative processing technologies is relevant. Solid state processes have been investigated for this application, namely friction stir welding. Recently, a variant has been exploited where local diffusion is the fundamental joining mechanism triggered by friction stir. The advantage of friction stir diffusion process is the minimal detrimental effect on both materials, preventing some critical identified problems. Since this process is not well developed, this thesis aimed to study friction stir diffusion process (FSDP) to join copper to stainless steel. Lap joints were produced varying processing parameters, namely, rotation and travel speeds and axial forging force. The effect of processing parameters on the width of effective joining was studied, as well the joints characterization for mechanical resistance properties and microstructural features at the interface. The thermo-mechanical conditions and time during the FSDP resulted in an interface with diffusion between both materials below 3 μm. The shear strength of the lap joints depends on the material thickness involved, but joining efficiencies up to 73.8 % were achieved.
