Ultrafine grained structure and mechanical properties of a LY12 Al alloy prepared by repetitive upsetting-extrusion

The process of repetitive upsetting-extrusion (RUE) was used to achieve severe plastic deformation, and its validity in preparing bulk ultrafine-grained materials was demonstrated by experimental investigation on a LY12 Al alloy. The results showed that the microstructure evolution of the alloy due to RUE processing was of a three-step character. With the increase of the RUE processing passes, i.e., the increase of the accumulated true strain, the grain size of the alloy gradually decreased, while the compressive yield stress, σ0.2, and the micro-hardness, Hv, increased correspondingly. In particular, after 10 passes of RUE processing corresponding to an approximate accumulated true strain of 8.926, an equiaxed ultrafine microstructure with an average grain size of about 200 nm was obtained. As a consequence, the σ0.2 and Hv of the alloy were enhanced from the starting 318.5 MPa and 112.3 Hv to 513.6 MPa and 176.5 Hv, respectively. The results also showed that the Hall–Petch relationship persists for the RUE-processed LY12 Al alloy with ultrafine grains down to 200 nm.