Friction Stir Welding of Steel-Aluminium Dissimilar Joints

Abstract

This research project aims to study the dissimilar joining of aluminum and steel using the friction stir welding (FSW) process. The study will establish the welding parameters effect on the joint microstructural evolution and the microstructure effect on the mechanical performance of such welded joint. The proposed configuration is a 2 mm thick butt joint involving AISI 1020 mild steel and aluminum alloy 6063-T6. Among the microstructural characteristics that will be evaluated, through the microstructural evolution study, should be highlighted the partial Al melting within the mixed zone and its relationship with Fe-Al intermetallic compounds formation. This task will involve techniques such as optical microscopy, microhardness, scanning and transmission electron microscopy, energy dispersive x-ray spectroscopy, backscatter electron diffraction, and x-ray diffraction. The mechanical performance of the joint will be evaluated through tensile and axial fatigue testing.In addition to the scientific interest, this study is driven by the necessity to reduce energy consumption in the transport industry, which is nowadays a very important factor on the design of vehicles. For this reason, the vehicles weight reduction, without compromising safety and structural integrity, is the objective of many studies searching for new materials and manufacturing processes. Among the most frequently explored materials in order to reduce weight are the aluminum alloys. Thus, the use of Al-alloys in vehicles components substituting steel is increasing rapidly. A critical issue in this material substitution is the steel-aluminum junction, which is commonly done using mechanical joining based on rivets, screws, etc. Fusion welding can not be used on such dissimilar joint due to metallurgical incompatibility. However, in many cases the mechanical joining solution has technical and economical issues that preclude the use of steel-aluminum joints in automobile structural components. Therefore, today there is an important technical and scientific activity on the development of technologies to efficiently join these two metallic materials. Some research has been performed using friction stir welding (FSW), with inconclusive but encouraging results. Therefore, a lot of work is needed to understand the microstructural evolution, mechanical performance, and the relationship between them, when the dissimilar joining of Al-steel is performed using FSW.