| Abstract Scope |
Dissimilar joining via resistance spot welding (RSW) has been long sought after in the automotive industry to improve energy efficiency, which is accomplished by lightweighting vehicles. Using advanced materials such as 6XXX series aluminum and dual phase steel alloys enables such design optimization, however joining such dissimilar alloy families proves challenging with traditional RSW due to the formation of brittle intermetallic compounds (IMCs). Automotive manufacturers mostly use Medium Frequency-Direct Current (MFDC) power supplies for RSW, which convert three-phase AC power from the bus bar to a direct current pulse delivered at the tips. While efficiently automated and optimized for similar metal joining, the MFDC RSW process has a longer cycle time (~500-1000 ms), which provides ample time and heat for IMCs to form when used with dissimilar materials such as aluminum and steel. Additionally, MFDC RSW requires cooling water to actively cool the electrodes. As an alternative, a new technology for resistance spot welding has been developed which delivers a much shorter and higher current pulse to the sheets without the need for water-cooled electrodes. This Medium Frequency-Frequency Converter (MF-FC) technology uses a power supply designed to deliver a single “DC” pulse to the sheets with a pulse width of 10ms, drastically reducing the potential for IMC formation with dissimilar welding. In this work, 6541-T4 Aluminum Alloy and Galvanized Dual Phase Steel with 600 Mpa UTS is joined using the MF-FC process. Parameter development is conducted with current range testing for 1, 2, and 3 pulses to form a lobe curve using peel testing evaluation. Static mechanical tensile shear testing and cross tension testing is also conducted. Optical microscopy reveals the nugget morphology and brings insight to how the two dissimilar materials interact during the very short welding process to form a joint. |