Effect of faying surfaces and characterization of aluminium AA6063-steel AISI304L Dissimilar joints fabricated by friction welding with Hemispherical Bowl, and Threaded Faying Surfaces

This work describes the effect of newly introduced faying surfaces on the microstructure and the mechanical properties of dissimilar weld joints of AA6063 and AISI304L alloys that fabricated through the rotary friction welding process (RFW). The experiments were done as six different experimental methods (‘A’ to ‘F’) at 1300 rpm rotation, 18 MPa friction pressure (FP), 24 MPa upset pressure (UP) and 5 sec friction time (FT) with the faying surfaces of hemispherical bowl and thread of 1 mm pitch on the weld specimens. The fabricated joints and the weld zones were characterized by macro and micro-study, Energy Dispersive X-ray Spectroscopy (EDS) spectrums, tensile properties, Vickers microhardness, impact toughness and fractography. The results showed that these faying surface modifications strengthen the bonding between the weld specimens and influences the performance of the joints. The hemispherical bowl showed better results than the threaded surfaces. Axial shortenings were within the acceptable limit in the range of 20–27 mm. Macro and microstructural studies showed the defect-free weld joints and the strong bonding between AA6063 and AISI304L alloys. The hemispherical faying surface on AISI304L alloy formed a U-shaped weld interface (WI) in the dissimilar joints. EDS proved the formation of the Fe-Al intermetallic and the element ‘O’ at weld zone. The joint efficiency for all the methods was around ≥ 100%. Maximum tensile strength was recorded as 238 MPa for method ‘F’. The threaded surface showed good hardness property nearby WI and method ‘A’ yielded maximum impact toughness for the joint.

Exploration of novel faying surface treatment for high-strength frictional bolted joints to enhance its after-slip performance

<p>Welded joints is adopted rather than bolted joints for megastructure’s connections because the former can carry large force. However, the former has several problems, such as quality control of welding in situ, which the latter can solve. By contrast, as the load transfer ratio of each bolt becomes uneven proportionally to the number of bolts, local slip around extreme bolts occurs before the whole slip. Extreme bolts to which a large shear force is applied will break before other bolts. For utilizing the strength of all bolts, the problem is solved by improving shear deformation capacity in faying surface with novel surface treatment. Here, the treatment concepts were explored, and the coating’s effectiveness was evaluated through friction tests. The deformation capacity can be twice or more than that of conventional treatment, and the slip coefficient doesn’t depend on contact pressure. These features have the advantage to give stable slip behaviour.</p>

SLIP COEFFICIENT OF BOLTED SLIP-CRITICAL CONNECTIONS

The design philosophy of slip-critical connections is to utilize the friction force developed through the clamping force exerted by the pretension of the high-strength bolt. Therefore, the slip-critical connections can have resistance in the direction of the bolt shear. This resistance is affected by the bolt clamping force and slip coefficient on the faying surfaces. This research aims to increase the resistance of the slip-critical connections. Increasing the resistance of the slip-critical connections can be achieved by increasing either the clamping force or the slip coefficient. Thermal spray coating technology was used to increase the slip coefficient. Tests were conducted to investigate the effects of coated material (aluminum or aluminum-magnesium) and coating thickness. Compared to the blast-cleaned faying surface, thermal sprayed coating faying surface results in a greater slip coefficient.