析出相对AZ91镁合金热轧板组织及边裂行为的影响

Effects of Precipitated Phase on Microstructure and Edge Crack Behavior of Hot Rolled AZ91 Magnesium Alloy Plate

采用光学显微镜(OM)、配有能谱(EDS)的场发射扫描电子显微镜(SEM)、室温拉伸试验等研究了析出相对AZ91镁合金在不同变形量和道次轧制后的微观组织、变形机制及边裂行为的影响。结果表明:对铸态AZ91镁合金而言,小压下量、多道次轧制可减少边部裂纹的产生,提高轧制成形能力;在轧制变形过程中,析出相由片层状向球状颗粒转变,且粒度更小,球状颗粒状第二相在轧制变形过程中可以通过促进孪晶细化和动态再结晶,从而有利于抑制裂纹的萌生;热轧后室温拉伸断口呈现较强的沿晶断裂特征,微裂纹主要分布在Mg/Mg_(17)Al_(12)相界面结合处及较粗大的第二相附近。在拉伸变形过程中,球状析出相颗粒可能成为微裂纹萌生的源头之一,微裂纹进一步扩展并形成宏观裂纹。

The effects of precipitated phase on the microstructure, deformation mechanism and edge crack behavior of hot rolled AZ91 magnesium alloy plate with different reduction per pass and rolling passes were studied by optical microscope, field emission scanning electron microscope equipped with energy spectrum and tensile testing at ambient temperature. The results indicate that multi-pass with small rolling reduction can reduce the edge cracks and improve the rolling forming ability for AZ91 magnesium alloy. Precipitated phase from the slice layer to spherical particles with tinier size during the rolling deformation is beneficial to inhibit the initiation of crack. The tensile fracture surfaces show obvious intergranular fracture features, and the microcrack primarily distributes around the Mg/MglTAlu phase interface and coarser second phase. Spherical precipitated phase particles could be prone to be one of the initiation sources of microcrack, and then the microcrack extends and turns to the macrocrack.