准原位腐蚀研究Sc含量对Al-Zn-Mg合金微观组织及耐蚀性的影响

本文研究了添加Sc对Al-Zn-Mg合金耐蚀性的影响。在Al-Zn-Mg合金中添加Sc可以更有效地阻碍热处理过程中的再结晶,增强其力学性能。添加Sc的合金在晶界析出中表现出显著的不连续性。此外,在Sc含量为0.29 wt.%的合金中,η相在晶界上的分布间距最大,避免了细小连续的η相为腐蚀提供通道,从而增强晶间腐蚀抗性。剥落腐蚀试验和微观结构再结晶分析表明,添加Sc对再结晶有抑制作用,从而提高了耐腐蚀性。准原位腐蚀试验结果表明,Sc含量为0.29 wt.%的Al-Zn-Mg合金的未腐蚀织构呈先快速减少后迅速增多的趋势,由此提出了在Al-Zn-Mg合金腐蚀初期,添加Sc对改善其表面织构和提高其耐蚀性具有重要作用的结论。

Microstructure and Mechanical Properties of TiC-Reinforced Al–Mg–Sc–Zr Composites Additively Manufactured by Laser Direct Energy Deposition

In order to refine the microstructure and improve the performance of direct energy deposited(DED)additively manufactured Al–Mg–Sc–Zr alloy,TiC-modified Al–Mg–Sc–Zr composites were prepared by DED and the effect of TiC content on the microstructure and performance was studied.In the absence of TiC particle,the microstructure of Al–Mg–Sc–Zr alloy prepared by DED consisted of fine grains with average size of 8.36μm,and well-dispersed nano-Al;(Sc,Zr)particles inside the grains and Mg;Si phase along the grain boundaries.With the addition of 1 wt%TiC,the microstructure of TiC/Al–Mg–Sc–Zr prepared by DED became finer apparently compared with that without TiC;while the further increase of TiC content to 3 wt%,the microstructure of TiC/Al–Mg–Sc–Zr prepared by DED became coarser with appearance of a new kind of needle-like(Ti,Zr);Si;phase.Also,the addition of TiC decreased the porosity of Al–Mg–Sc–Zr prepared by DED.Simultaneously,after the addition of TiC,the tensile strength increased from 283.25 MPa to 344.98–361.51 MPa,and the elongation increased from 3.61%to 9.58–14.10%.The potential mechanism of the microstructure evolution and strength improvement was discussed.This research will provide new insights into the available metal matrix composites by laser additive manufacturing(LAM).

Effects of bottom deflectors on aerodynamic drag reduction of a high-speed train

Inspired by the fact that bogies and bottom equipment generally contribute a great deal of aerodynamic drag to high-speed trains,this paper puts forward a simple method of mounting some small deflectors before and/or after the bogie cabins to optimize the underbody flow and reduce the aerodynamic drag of high-speed trains.The flow fields of the high-speed train models with and without bottom deflectors are numerically studied by the IDDES method.The effectiveness and further mechanism of the bottom deflectors on aerodynamic drag reduction are analyzed.It is demonstrated that the bottom deflectors could guide the underbody flow to the ground and prevent it from hitting on the bogies and bottom equipment of the train,resulting in a significant aerodynamic drag reduction effect.Moreover,the effects of different mounting locations of bottom deflectors on drag reduction are discussed as well,and an optimal mounting configuration with a drag reduction effect of up to about 12%is finally obtained.Nevertheless,the mounted deflector is also proved capable of significantly reducing the interference range of the underbody flow and reducing the slipstream of the train,which possesses a higher guarantee for the safety of railway workers and passengers waiting on the platforms.This work provides a new idea for aerodynamic drag reduction of high-speed trains,and is of great significance in energy conservation and consumption reduction.

Microstructures and Mechanical Properties of Al-Mg-Sc-Zr Alloy Additively Manufactured by Laser Direct Energy Deposition

An Al-Mg-Sc-Zr alloy was additively manufactured by laser direct energy deposition(DED)under different laser powers,and the microstructures and mechanical properties of the as-deposited samples were investigated.The samples showed a fully equiaxed grain structure with grain sizes of 2–30μm.Most of the blocky primary Al3(Sc,Zr)-precipitated phases(<5μm)were arranged along the grain boundaries.A small amount of fine granular secondary Al3(Sc,Zr)phases(<0.5μm)were precipitated owing to the cyclic heat treatment during the DED forming process.According to the EBSD(Electron backscatter diffraction)results,the texture index and strength of the sample were only slightly greater than 1,indicating that the material structure exhibited a certain but not obvious anisotropy.The sample in the horizontal direction had better yield strength,tensile strength,and elogation properties(399.87 MPa,220.96 MPa,9.13%)than that in the building direction(385.40 MPa,219.40 MPa,8.24%),although the sample in the〈XOZ〉plane had the finest equiaxed grains.The ductility of the〈XOZ〉sample deteriorated as the number of pores increased.