Researchers from Turin Technical University reviewed several dissimilar welding technologies in dissimilar joining among steels and wrought aluminum alloys in cars
Stringent regulations of carbon dioxide emissions and fuel economy have led car manufacturers to focus on novel approaches to decrease car-body weights, without compromising performance of the car and avoiding excessive cost increases. The approach of multi-material (or hybrid) car bodies includes development of different parts with different alloys belonging to the same class or with entirely different material classes. Such hybrid approach uses lighter or more advanced materials only where they can achieve the maximum benefit to decreases the car weight at a reasonable cost. Fusion welding methods such as the resistance spot welding technique are commonly used for joining steel car bodies. However, these approaches have certain shortcomings when they are applied to hybrid welding between aluminum and steel.
Now, a team of researchers from Turin Technical University, in collaboration with FIAT Research Center, compared the mechanical properties of the hybrid joints obtained between aluminum alloy and steel sheets by using different techniques. The results were published in the journal MDPI Metals on March 11, 2019. The team found that the tensile shear force that was obtained from different methods differs between about 2 and 8 kilonewtons (kN). However, the results become closer when the same force is normalized against the thickness of the aluminum sheet. In the resistance spot welding methods, the thickness of the intermetallic compounds (IMC) interlayer is generally less than 5 µm and the tensile shear force is in the range of 4 to 8 kN.
The team used a bimetallic (roll bonded) interlayer in resistance spot welding (RSW) and obtained the greatest tensile shear force even if the IMC layer was somewhat thicker than in plain RSW. However, the process tape and cover plate techniques failed to attain significantly better results than plain (optimized) resistance spot welding. In case of the solid state spot welding methods: ultrasonic spot welding and friction stir spot welding, the team obtained lower tensile shear force compared to those achieved by plain resistance spot welding. The variation can be attributed to smaller thickness of the aluminum sheets that were used in the research. The team achieved a significantly larger tensile shear force than most RSW processes in case of resistance element welding and friction bit joining processes. The team concluded that the aluminum sheet thickness and base-metal strength majorly define the overall tensile shear force.
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