•Grain refinement and work hardening were achieved by HFIR.•The effect of MgZn2 on grain refinement process was investigated.•Surface nanocrystallization model of aging Al-Zn-Mg alloy was established.Al-Zn-Mg alloy specimens before and after aging treatment were processed through high-frequency impacting and rolling. Grain refinement and work hardening were achieved in a certain depth from the top surface of specimen. Surface nanocrystallization mechanism was analyzed by TEM. The effect of precipitated phase of MgZn2 on grain refinement process was investigated in detail. The schematic illustration of grain refinement process of aging Al-Zn-Mg alloy was established. Results show that the role of precipitated phase is the crossing point of sub-grains boundaries and the obstacle of dislocation motion.

An optimization-based numerical procedure was developed to determine the tool temperature-dependent heat-transfer coefficient (HTC) between the blank and tools during the hot stamping of boron steel. During the quenching period, HTC decreased with the increasing tool temperature. There was no obvious linear relationship between the two. The HTCs were 2493 and 856 W m−2 K−1, respectively, under the tool temperatures of 373 K and 723 K (100 °C and 450 °C).

•The new prolong life method of MSF about welded joint was put forward.•The low transformation temperature alloy powder was applied to the method of MSF.•The fatigue strength of LTT-joint increases by 74.07%.Modification of spraying fused (MSF) of plasma arc as heat source was used to improve the fatigue performance of welded joint, which both fundamentally reduced stress concentration at weld toe and achieved metallurgical bond between spraying fused coating and welding. The low transformation temperature alloy powder was applied to the method of MSF. After spraying fusion, especially spraying fused joint by low transformation temperature alloy powder, the distribution of residual stress is more difficult to be obtained. Finite element (FE) simulation as an important tool was used to determine the stress field and temperature field of spraying fused joint. Simulated results show that as-welded joint and welded joint spraying fused by conventional nickel base alloy powder (Conventional-joint) present tensile stress. The stress of welded joint spraying fused by low transformation temperature alloy powder (LTT-joint) is compressive stress. Fatigue test results indicated that under the condition of 2 × 106 cycles, the fatigue strength of as-welded joint is 135 MPa, while that of Conventional-joint and LTT-joint is 218 MPa and 235 MPa, respectively. The fatigue strength of Conventional-joint increases by 61.48%, and fatigue strength of LTT-joint increases by 74.07%.