Characterization of multi-pass friction stir processed AA1050 and AA6082 dissimilar joint

Abstract

Due to their decreased weight, superior fatigue properties, high strength to weight ratio, good workability/formability, and corrosion resistance, aluminium-based metal matrix composites have emerged as appropriate materials for the automotive and aerospace industries. Recently, the joining of dissimilar metals has seen a lot of success in a variety of fields. Friction stir processing (FSP) has been used to create metal matrix composites of base metals such as aluminium, copper, iron, and nickel. Friction stir processing (FSP) is a new solid-state technology that modifies the microstructure of metals using the principles of friction stir welding. It improves strength and ductility, increases corrosion and fatigue resistance, and enhances hardness and formability by removing casting defects and refining microstructures on a local level. The influence of process factors on the microstructure was characterized after a single pass in the majority of FSP studies. Multiple passes of FSP, on the other hand, are another way to further change the microstructure of Al castings. The majority of the literature on multi-pass FSP focuses on plate processing rather than joint processing, according to the accessible literature. Only a few studies have been published on multi-pass friction stir processed joints. As a result, more research into multi-pass friction stir processing on dissimilar aluminium alloys is required. The aim of this research is to determine the impact of a multi-pass friction stir processed joint of dissimilar aluminium alloys AA1050 and AA6082. The knowledge gained from this study will serve as a guide for related sectors in determining the expected outcome of using this technique on dissimilar aluminium alloys. Two aluminium alloys AA1050 and AA6082 plates were welded utilizing the friction stir welding process prior to the joint’s analysis. After that, the welded joints were friction stir processed using the same parameters as the FSW. The friction stir processed joints were then cut with a water jet cutting machine and prepared for various analyses. This involved the macrostructure, microstructure analysis, tensile tests, bending tests, hardness tests, and SEM. These tests were carried out to see how the multi-pass FSP will affect the previously friction stir welded joints. The described specimens were cut from several points on the plates, such as the plate's beginning, middle, and end. The following symbol was used to represent the cut positions on the processed plates to symbolize their positioning (S for the start, M for the middle and E for the end of the plate). There were twelve generated specimens for each plate. Different tests were done on the cut specimen. On the basis of the test findings, conclusions were drawn. The microstructural analysis revealed that as the number of passes increased, the grain sizes decreased, and the distribution of grain sizes became more uniform across the processed zone, regardless of material position. The grain structure of the multi-pass friction stir processed 1050/6082 and 6082/1050 FSPed joints was refined from 19.84 μm to 5.381 μm for the 1050/6082 and from 13.12 μm to 1.744 μm for the 6082/1050 FSPed joints. The joint with 6082 on the advancing side exhibited significantly finer grains (1.744 μm) than the joint with AA1050 on the advancing side (5.381 μm). As the number of passes increased, the grain sizes decreased and the distribution of grain sizes became more uniform across the processed zone, regardless of material position. The ultimate tensile strength (UTS) increased as the number of FSP passes increased when AA1050 was put on the advancing side. When AA6082 was positioned on the advancing side, the UTS varied across specimens taken from different locations of the FSPed joints. The maximum ultimate tensile strength was 86.1 MPa for the AA1050/AA6082 and 79.3 MPa for the AA6082/AA1050. When compared to both base materials, the percentage elongation of all joints was determined to be greater. The SEM fractographs of the fractured surface for the AA1050/AA6082 FSPed joints indicated ductile trans-granular failure features and the AA6082/AA1050 was characterised by ductile trans-granular failure and brittle failure features. The Vickers microhardness of AA1050/AA6082 FSPed joints increased towards AA6082, whereas the Vickers microhardness of AA6082/AA1050 FSPed joints decreased towards AA 1050 regardless of the number of passes. With AA1050 on the advancing side, the stir zone achieved a maximum hardness of 65.54 HV and when AA6082 was on the advancing side, the stir zone achieved a maximum hardness of 61.06 HV. The deflection for the processed joints was detected in various regions of the joints, with some of the joints showing cracks and others being crack-free. There was no particular trend in Ultimate Flexural Strength that was observed during analysis. For AA1050/AA6082 FSPed joints, the average UFS of the root was found to be greater than that of the face, with the maximum UFS attained at 381.34 MPa for the root and 359.37 MPa for the face while for the AA6082/AA1050 processed joints, the average UFS of the root was higher than that of the face, with the maximum UFS obtained at 353.75 MPa for the root and 258.75 MPa for the face. The data has revealed that multi-pass friction stir processing has an effect on joint mechanical properties irrespective of material positioning. This may be observed in the AA1050/AA6082 and AA6082/AA1050 FSPed dissimilar joints. As a result, it can be concluded that multi-pass friction stir processing improves mechanical properties significantly.