Achieving three-layered Al/Mg/Al sheet via combining porthole die co-extrusion and hot forging

Al/Mg/Al sheet with good bonding quality and mechanical properties was fabricated based on the proposed porthole die co-extrusion and forging (PCE-F) process. There were no voids, cracks or other defects on the Al/Mg interface. A continuous diffusion zone with two-sub-layer structure was formed across the Al/Mg interface, and its width increased with higher temperature or reduction ratio. The sub-layers formed at low and high temperature were identified to be solid solutions and intermetallic compounds (IMCs) including γ-Mg17Al12 and β-Al3Mg. In Al layer, the welding zone mainly consisted of fine equiaxed grains with several coarse elongated grains, while the majority of matrix zone is coarse elongated grains. The rolling textures were dominated in both welding and matrix zones. In Mg layer, the welding zone exhibited complete DRXed grain structure, while several unDRXed coarse grains were observed in the matrix zone. With the increasing temperature, the grain size of Al and Mg layer firstly decreased and then increased. High reduction ratio strongly refined the grain structure of Al layer, while slightly affected the Mg layer. The Al/Mg/Al sheet experienced stress-drops twice during the tensile test. The first stress-drop was determined by the IMCs and microstructure of Mg layer, while the second stress-drop was closely related to the microstructure of Al layer. Al/Mg/Al sheet forged at the lowest temperature without the formation IMCs exhibited the highest stress for the first stress-drop, and that forged under the highest reduction ratio with the smallest grain size in Al layer had the highest stress for the second stress-drop.