INVESTIGATION OF FRICTION STIR SPOT-WELDED DISSIMILAR ALUMINUM AND STEEL METALLIC LAP JOINTS THROUGH EXPERIMENTAL APPROACHES

This work aims to investigate the feasibility of joining two dissimilar metals, aluminum 7075 and low-carbon steel SAE1006 plates, with a high-quality weld. The processing parameters were different design of Tungsten carbide tool steel (WC) tools, three dwell times of 15, 17 and 20 sec, and a constant rotational speed of 1250rpm. The effect of processing parameters on the microstructure, mechanical behavior was investigated. Results showed that long tool pins increased the microhardness of the upper aluminum plate significantly. Long pins had greater tensile shear strengths than short ones because they were influenced by the tool shoulder. Among all factors, tool pin length had a more noticeable beneficial impact on properties obtained compared to dwell time. At a high pin length and a 17sec dwell duration, the highest temperature attained was 487°C. The joint interface area was observed using an optical electron microscope. Mechanical strength tests (lap shear test and micro hardness test) were carried out to see changes in grain properties through analysis of weld zone’s microstructure. The tensile shear strength for tools with long pin exceeded that for short ones due to effect from the tool shoulder region. Brittle mode of fracture was exhibited by both short and high pins under all conditions used for this research study. At those conditions which involved a long dwell time under higher pin length, maximum tensile shear strength recorded was found to be 82.4 MPa. The maximum micro hardness was 205 HV and was achieved at 20 sec dwell time and using the tool with longest pin.