Joining of steel and aluminium alloy using tig welding with improved mechanical properties

Abstract

Joining dissimilar metals is essential nowadays in manufacturing and constructing advanced machineries and equipments. Dissimilar weld is used in order to minimize material cost, maximize performance and reduce the vulnerability to failure and maintenance, therefore it can be used to create mechanically robust joints between parts composed of dissimilar metals in marine, automotives, aerospace, boiler, medical applications, transport system. Aluminum Alloy and steel dissimilar welding processes yield unwanted disadvantages in the weld joint due to the large difference between the aluminum alloy and steel melting points and the nearly zero solid solubility between these two metals produces brittle intermetallic compounds (IMCs). The objective of this thesis was to study the effect of process parameters particularly on the IMC layer thickness and properties of TIG welded dissimilar sheet metal joint. To increase the strength of the dissimilar weld it is necessary to decrease the IMC layer thickness of the welded joint. To decrease the IMC layer thickness the heat input is decreased by lowering the welding current, increasing the heat dissipation rate by using a water cooled copper block setup and using the coating of zinc which is present on Galvanised steelas a barrier layer. The welding of Aluminium 6061 alloy is done with two steels – mild steel and galvanized steel separately. Welding current in the range of 70A and 90A was used as process variables. The welded joints were examined by different characterization techniques such as macroscopic, optical microscopy and scanning electron microscopy, EDS analysis, XRD analysis, tensile testing and micro hardness measurements. From bead on the steel sheet experimental and lap joint experiment, it was seen that on decreasing the heat input, inceasing heat transfer rate and with a barrier layer of zinc the minimum IMC thickness achieved was 11.9 microns, and with normal conditions the maximum IMC thickness observed was 20.5 microns. It was found that the thickness of the IMC layer decreased and the tensile strength of the lap joint increased with the increasing heat transfer rate of welded zone and by introducing a barrier layer.