As part of the ALLEGRO project, AA 7075 sheets were successfully joined using Magnetic Pulse Welding (MPW). MPW is a high speed solid state collision and joining process, therefore it is mainly used for joining dissimilar or not classically weldable materials. These include AA 7075, an alloy that offers enormous lightweight potential due to its high strength, but is susceptible to hot cracking using fusion based welding processes. As AA 7075 in the artificially aged condition (T6) could not be successfully joined using MPW, suitable heat treatments were developed and investigated to overcome that limitation. The objective of the investigations is to prove the weldability of AA 7075 as sheet metal joint by means of MPW and to achieve good mechanical properties and a favorable weld seam interface. In this investigation, it is shown that different heat treatment strategies enable MPW for AA 7075. Good mechanical and metallographic joint properties are obtained and examined in the context of MPW process and heat treatment parameters.

Based on the mechanical properties under quasi-static stress and the analysis of the weld seam interface, the characterization of the joints is carried out and the best heat treatment is determined. The maximum joint strength is 370 MPa and failure under load occurs outside the weld seam in the AA 7075 base material. Partial recrystallization in the way of very fine grains is present in the weld interface and the interface shows typical MPW characteristics such as waves and a non bonded zone at the middle of the collision area. The best heat treatment for MPW of AA 7075 consists of a short time solution annealing followed by rapid quenching in water and conclusive aging for 20 hours, with the MPW joining process performed during the heat treatment process right after quenching.