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Alternating extrusion (AFE) is a new way to effectively alter the texture and enhance the mechanical properties of the extruded bars. However, the mechanisms of microstructure evolution and enhancement of hardness are still unknown by different extrusion ratios (ERs) during extrusion. This work systematically investigated the microstructure and hardness of AZ31 alloy with various extrusion ratios of 8.1, 15.6, and 24.8 by electron backscattered diffraction. The most striking result to emerge from the data is that when the ERs were increased from 8.1 to 15.6, the grain size was refined to 7.13 μm. However, when the ER reached 24.8, the average grain size was 11.43 μm. The proportion of recrystallization was only 2.92%, there was a continuous rotation of sub-grains at coarse grain boundaries, and non-basal slip < a > dislocations were activated and enriched near low-angle grain boundaries. At present, the recrystallization has not been completed. The grains of the product are coarsened, and the hardness is reduced. When λ = 15.6, the AFE has a significant grain refinement effect and the highest hardness value.

Traditional rolled (TR) aluminum (Al)/magnesium (Mg)/aluminum (Al) composite plates have many bottlenecks such as multiple passes, low interlaminar strength, and weak mechanical properties. In this paper, the hard-plate rolling (HPR) method was used to prepare Al/Mg/Al composite plates under a single pass reduction of 60%. The results show that the ultimate tensile strength (UTS) of the composite plate obtained by hard-plate rolling is 262.3 MPa, and the percentage of total elongation at fracture (A t ) is 12.3%, which is 31.6% and 37.4% higher than that of the traditional rolling, respectively. It is attributed to the unique corrugated interlocking structure of the interface of the composite plate caused by hard-plate rolling. The shear texture produced by the Mg plate weakens the strong-basal texture. At the same time, the strong basal slip and the large amount of energy stored in the deformed grains provide favorable conditions for dynamic recrystallized (DRX) nucleation. The microstructure is deeply refined by DRX, and the strength and plasticity of the composite plate are improved synchronously. It provides scientific guidance for the development of high-performance lightweight composite plates and the research on hard-plate rolling technology and also has good industrial production and application potential.

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