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A high extrusion ratio of 166:1 was applied to commercial AZ61 alloy in one step with an extrusion speed of 2.1 m·min−1. The effects of DA (direct aging) treatment on the microstructure and tensile properties of extruded alloy were investigated. The extruded alloy exhibits fine DRXed grains and the average grain size is ~11 μm. After DA treatment at 170 °C, the tensile strength and 0.2% offset yield strength is enhanced from 314 to 336 MPa and from 169 to 191 MPa respectively, sacrificing elongation from 26.5% to 23.3%. The grain size and texture distribution of extruded AZ61 scarcely evolve during the post aging treatment. However, the enhanced strength in peak-aged alloy is mainly caused by the high-density elliptical Mg17Al12 precipitates distributing uniformly along the grain boundaries or within the grains, by precipitation and dispersion hardening. Furthermore, the nano-sized precipitates effectively inhibit grains from coarsening by triggering pinning effects along the grain boundaries at elevated temperature. As a result, the peak-aged alloy exhibits a better superplasticity of 306.5% compared with that of 231.8% of extruded sample. This work provides a practical one-step method for mass-producing Mg alloy sheets with excellent tensile strength and ductility compared with those fabricated by conventional extrusion methods. [ABSTRACT FROM AUTHOR]

In this study, an innovative method, wherein trace in situ synthesized nano-(TiC+TiB 2) particles are added forged H13 steel, was designed and used to manipulate its microstructure. This refined the grains and laths martensite, increased the retained austenite and carbides, and controlled the carbide segregation. Thus, the strength, plasticity, and toughness of the steel were simultaneously improved. Among the samples, the H13 steel, manipulated by 0.02 wt% nano-(TiC+TiB 2) particles, exhibited the best mechanical properties. Its yield strength, tensile strength, elongation, unnotched impact toughness and U-notch impact toughness increased by 11.6%, 7.6%, 14.2%, 35.0% and 33.8%, respectively, and reached 1142 MPa, 1426 MPa, 16.9%, 449.3 J/cm2, and 41.39 J/cm2, respectively. The main strengthening mechanisms were grain boundary strengthening, dislocation strengthening and dispersion strengthening. This study provides a new method for the bonding between ceramic nanoparticles and steel and provides a novel idea for the development of high-performance and low-cost steel. • The nano-(TiC+TiB 2) particles (NPs) are beneficial to nucleation of γ-Fe/α-Fe. • The trace nano-(TiC+TiB 2) particles inhibited carbide segregation of H13 steel. • More and fine carbides and austenite are yielded by adding trace nanoparticles. • The H13 steel with high comprehensive properties is prepared by adding trace NPs. [ABSTRACT FROM AUTHOR]