共晶Si形貌对A356铝合金动态、准静态压缩力学性能及氢脆的影响

Effect of Eutectic Si Morphology on Dynamic and Quasi-static Compression Mechanical Properties and Hydrogen Embrittlement of A356 Aluminum Alloy

共晶Si形貌与A356铝合金的动态、准静态压缩变形下的力学性能及抗氢脆性能的影响密切相关。因此文章通过Material Test System(MTS)及霍普金森压杆(SHPB)测试变质前后A356铝合金的动态/准静态压缩力学行为,并采用电化学充氢方法研究合金的抗氢脆性能。结果表明,准静态压缩变形后,合金中板状共晶Si垂直于压缩方向破裂成颗粒状。细化后的共晶Si提高了合金的塑性,延缓了合金的失效。而动态压缩变形后,板状共晶Si变形不均匀,并且碎成块状的共晶Si的尖端在压缩过程中会切割基体,导致其附近出现裂纹等缺陷。随着应变速率增大,铸态A356合金的屈服强度及抗压强度逐渐增大,合金具有一定的应变速率敏感性。变质后,共晶Si得到细化,增大了Al/Si接触面积,共晶Si捕获原子氢后降低了其与基体的连结,导致合金在拉伸变形过程中裂纹更易沿其扩展,并且细化后的共晶Si会进一步降低合金的抗氢脆性能力。其中细化后残存的块状共晶Si在捕获原子氢后会出现脱粘现象,易成为裂纹萌发点。

The morphology of eutectic Si is closely related to the mechanical properties and hydrogen embrittlement resistance of A356 aluminum alloy under dynamic and quasi-static compression deformation.Therefore,this paper investigated the dynamic/quasi-static compression mechanical behavior of A356 aluminum alloy before and after modification by using Material Test System(MTS)and Split Hopkinson Pressure Bar(SHPB)techniques.The hydrogen embrittlement resistance of the alloy was also studied by electrochemical hydrogen charging.The results showed that after quasi-static compression deformation,the plate-like eutectic Si in the alloy fractured into granular shape perpendicular to the compression direction.The refined eutectic Si improved the plasticity of the alloy and delayed the failure of the alloy.However,after dynamic compression deformation,the plate-like eutectic Si deformed unevenly and the tip of the fragmented eutectic Si cut the matrix during compression,leading to the appearance of defects such as cracks near it.With the increase of strain rate,the yield strength and compressive strength of the as-cast A356 alloy gradually increased,and the alloy showed a certain strain rate sensitivity.After modification,the eutectic Si was refined,the Al/Si contact area was increased,and the eutectic Si captured atomic hydrogen,reducing its connection with the matrix.This made the alloy more susceptible to crack propagation during tensile deformation,and the refined eutectic Si further reduced the hydrogen embrittlement resistance of the alloy.The remaining blocky eutectic Si after refinement would experience debonding after capturing atomic hydrogen,which could become the crack initiation site.