In this paper, high-strength steel is prepared by different heat-treatment processes. Through split Hopkinson pressure bar experiment, optical microscope, scanning electron microscope and X-ray diffractometer, the microstructure evolution and mechanical behaviour under high strain rate were studied. The results show that the samples prepared by the two-step isothermal method have the highest compressive strength under the same strain rate, especially at 5000 s−1, the highest can reach 2097 MPa. The retained austenite undergoes transformation under high strain rate conditions, which improves the plastic deformation ability of the material. Compared with the one-step isothermal heat-treatment process, the two-step isothermal heat-treatment process can better control the strength and plasticity under high strain rate deformation conditions.

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In this paper, the effect of Er on the hot cracking behaviour of Al-5Cu alloy is investigated by the means of wedge moulds, differential hot analyzer, optical microscope, and scanning electron microscope. The results show that the percentage of intergranular low-melting-point eutectic structure is increased by approximately 8% on average per 0.3 wt-% Er additions. The increase of low-melting-point eutectic structure enhances the fluidity of the liquid film in the late solidification stage, resulting in the improvement of the hot cracking resistance of the alloy. Moreover, the Al-5Cu-0.6Er alloy has the best hot cracking resistance under wedge-shaped copper casting experiments.