Joining of steel to aluminium and stainless steel to titanium for engineering applications

摘要

Dissimilar welding has been subject of several investigations due to its potentialimportance in various industrial fields such as transportation, energy generationand management. Dissimilar welding can increase the design efficiency, by the useof complementary alloys with different properties, cost cutting and light weightingstructures. The use of different materials within a component or structure to bestsuit a particular task, requirement or increase its life and performance has alwaysbeen an ambition of several designers and engineers.This project investigated the joining steel and aluminium for the automotive industryand also stainless steel and titanium to be applied in the civil nuclear energygeneration industry. These dissimilar metallic combinations are metallurgicallyincompatible and the formation of brittle intermetallic phases (IMC) need to becontrolled or eliminated.To join steel to Al, laser spot welding process was selected, to avoid the bulkmelting of steel and Al at the joint interface that enhance the formation of brittleIMC. This part of the work was focused in controlling the joining process to controlthe IMC formation of galvanized and uncoated steel to Al and verify if it waspossible to have a sound and reliable joint in the presence of an IMC layer.In the second part of this study, stainless steel to titanium joining, a differentapproach was taken with the application of weld metal engineering to modify oreliminate the IMC formation. Several metals were evaluated as potential interlayersto use and laser welding with a Ni interlayer was evaluated with moderate success,due to the modified IMC with improved mechanical properties and the goodcompatibility between Ni and the stainless steel. A further improvement wasachieved when Cu was brazed between stainless steel and Ti using CMT (ColdMetal Transfer) a low heat input MIG process. The final attempt was to use adifferent interlayer that was 3D printed and deposited in several layers. Thisinterlayer was composed Cu and Nb that were selected as candidates to avoid theIMC formation between the stainless steel and Ti. With this approach it waspossible to build an IMC free component and possibly improve and avoid IMCformation in several other dissimilar metallic combinations.