PSI - Issue 61

Jignesh Nakrani et al. / Procedia Structural Integrity 61 (2024) 188–194 Jignesh Nakrani et al. / Structural Integrity Procedia 00 (2019) 000 – 000

189

2

1. Introduction The demand for more efficient and lighter systems drives the development of hybrid structures. Hybrid structures, especially those combining different materials like aluminum (Al) and steel, are of interest due to their diverse uses in industries such as aerospace, marine, railway, and automotive as indicated in Eyvazian et al. (2020). Friction stir welding (FSW) exhibited potential for fabrication of dissimilar joints at temperatures below their melting points Aghajani et al. (2019). The study of fatigue crack growth behavior of such dissimilar welds is crucial due to the cyclic loading experienced in various applications. To prevent failures, conducting a damage tolerance analysis becomes essential Kalnaus et al. (2008). In recent years, numerous studies have delved into the FSW parameters impact on tensile behavior of dissimilar joints comprised of various steels and Al alloys. Chen et al. (2009) investigated the impact of varying traverse speeds on the FSW of Al6061 and SS400, concluding that lower rotational speed and traverse speed yielded best impact toughness and acceptable tensile properties. Ghosh et al. (2014) explored influence of tool rotational speed on Al6061 SS304 FSW joints and achieved high tensile strength for the optimal tool rotation speed of 710 rpm. Habibnia et al. (2015) implemented different tool offsets (0, 0.8, and 1.5 mm) for FSW of SS304 and Al5050. The objective was to mitigate pin erosion during the process by reducing overheating. For tool offset of 1.5 mm, rotational movement of the tool resulted in abrasion along the steel sheet edge. This abrasion promoted the steel particles distribution evenly in stir zone, resulting in fewer defects. Murugan et al. (2018) explored the impact of altering tool rotation and travel speed on the tensile behavior of joints prepared from commercially pure Al and SS304 using FSW. The increase in tool rotation speed promotes brittle intermetallic compounds which deteriorate the tensile strength. Pankaj et al. (2022) analyzed tool position impact on the microstructure as well as mechanical properties of DH36 steel and Al6061 dissimilar FSW joints. The tensile strength increased when the tool offset gradually increased starting from 0.4 to 1.5 mm. However, tensile strength started decreasing when the tool offset was further increased from 1.5 to 2.5 mm. While the tensile behavior of FSW joints made of steels and Al alloys are extensively studied, the literature available on their fatigue properties is limited. Okane et al. (2017) performed the fatigue life analysis of dissimilar FSW joints of Al6063 and carbon steel. A significant improvement in fatigue strength was reported from a heat treatment process. Uematsu et al. (2020) studied the crack propagation at the interface of Al6061 and SS304 joints prepared using the FSW process. Their findings indicated that FCGR was not affected significantly due to post-weld heat treatment. Considering the limited research available in this domain, it is essential to conduct more comprehensive investigations into fatigue crack propagation in joints prepared from steels and aluminum alloys. Our study explores how the initial notch location affects fatigue crack growth in SS304-Al5083 friction stir welded joints. This is important because such joints may develop cracks at various points, but this hasn't been studied before. In the present study, the dissimilar joints between SS304 and Al5083 base materials (BMs) are fabricated using the FSW method. Tensile and FCGR tests of base materials and FSW joint are conducted to quantitatively evaluate crack growth rates. For the FCGR tests, two notch locations are considered: one at the interface and the other offset towards the aluminum side. 2. Experimental methodology 2.1. Materials and Friction Stir Welding Process Rolled plates of SS304 and Al5083 (250 mm × 70 mm × 3 mm size) were used in the present study. The dissimilar joint was prepared by friction stir welding. Chemical composition of the BMs is given in the Table 1.

Table 1. SS304 and Al5083 chemical composition (wt%). Material Cr Ni Mn, Si C

Fe

Mg

Al

SS304 Al5083

8-10

18

1-2

0.15

Bal 0.4

-

-

- Bal The butt joints of SS304 and Al5083 alloys were fabricated using friction stir welding (FSW) using a CNC milling. Mandrel made from H13 steel was used to hold tungsten carbide friction stir tool having a cylindrical pin of 4 mm - 1 - 4-5