Institute of Fundamental Technological Research

Friction stud welding process is a suitable candidate in joining stud fasteners for steel structure buildings, military vehicles, automobiles, aircraft, ocean liners, bridges, ship buildings, etc., The peak temperature for welding is achieved by converting mechanical energy to thermal energy at the sample interface without the use of electric energy from other sources because it is a solid-state process. The study of the thermal behavior of different metals during friction stud welding is very important since it is a thermal energy process. However, there is no good thermal model for the friction stud welding process. In this work, the generation of heat flux at the interfacial area of two distinct metals, namely aluminum and mild steel, is calculated using a mathematical model. The temperature at the interfacial region, which plays a significant role in the quality and strength of the weld component, is particularly focused on experimentation and analytical modeling. In the experimentation, a noncontact type infrared thermometer is used to measure temperature directly. The temperature profile was determined by the finite difference method based on thermal resistance and capacitance formulation at transient conditions. The obtained mathematical results are compared with the experimental results at the distance of 5 and 10mm from the welded interface. The computed temperature profile is in good agreement with the experimental data on the heating side and with a minimum degree of deviation in the cooling part. The maximum percentage of error for the 5mm interface is 3.349 and for the 10mm interface is 2.857. This deviation is due to the zero-axial shortening assumption in the analytical model. Besides, the temperature characteristics of the welded are analyzed at various time increments by numerical simulation. As a result, the predicted temperature is more on the aluminum side compared to the mild steel due to a change in thermal properties. This proposed thermal model would be helpful to improve the design and manufacture of welding machines.

friction stud welding, thermal modeling, finite difference method, numerical simulation, aluminum, mild steel

In the present scenario, aerospace and automobile industries depend on lightweight materials such as magnesium and aluminum alloys because of their great balance between mechanical properties and weight ratio. Despite these benefits during the joining process of these dissimilar materials by welding, many challenges arises. The prominent one is related to the low melting points of these lightweight metals which make it almost impossible the joining using conventional arc welding techniques. To tackle this challenge, Friction Stir Welding (FSW) can be considered as a promising candidate tool. In this study, to demonstrate the FSW performances of joining two dissimilar materials we have investigated the joining of AA 6061 and Mg AZ 31 B using a built-in house a modified milling machine. The dissimilar combinations of AA 6061 and Mg AZ 31 B joints were successfully joined by embedding different welding conditions and varying the offset distance. The mechanical performances were evaluated by conducting specific mechanical tests such as micro-hardness, tensile, and impact tests, respectively. To explain the mechanical results, we have applied optical microscopy observation on the microstructure associated with the bonding location. The results prove that the strength of the Friction Stir Welded joints is much higher as compared to other techniques especially in terms of dissimilar metals.

friction stir welding, aluminum, magnesium, mechanical properties