等径角挤压Al-3%Si合金裂纹的萌生及扩展

Formation and growth of cracks in Al- 3%Si alloy during ECAP

使用内角为105°和外角为37°的模具对Al-3%Si合金进行了A路径等径角挤压实验,采用光学显微镜和扫描电镜观察了试样裂纹的萌生和扩展,结果表明,Al-3%Si合金在A路径经过3道次挤压后,观察到材料上表面(与模具内角接触的表面)有裂纹出现,随着挤压道次的增加,应变累积量不断积累,裂纹由浅到深,由小到大发生变化。分析认为:材料在ECAP变形过程中材料上表面变形剧烈,随着挤压道次的增加,脆硬相共晶Si发生碎断,碎断后的共晶Si偏离基体ɑ-Al并伴随凹坑出现,脆硬相共晶Si和空穴处产生应力集中导致裂纹萌生;裂纹在表面拉应力和剪切力的作用下进行扩展。

Based on Al -3% Si alloy, the ECAP test through route A was carried out by die with inner angle 105° and outer angle 37° and the formation and growth of crack were observed by OM and SEM. The results show that there are cracks on the upper surface of the sample （surface contacting with the inside corner of die） after three-pass extrusions in route A for AI -3% alloy. With the increasing of extrusion passes, the amount of the strain accumulation increases gradually, so the crack is changed from shallow to deep and small to big. Analysis shows that the intense deformation is produced on the upper surface during ECAP process, and with the increasing of extrusion passes, the hard brittle phase euteetic Si is chopped and deviated from matrix α- Al with pits appearance. Crack formation is caused by stress concentration produced in brittle eutectic Si and holes, and the crack expands under tensile stress and shear force of the surface.