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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。
A-path angular extrusion of Al-3% Si alloy was carried out using a mold with an internal angle of 105 ° and an external angle of 37 °. The crack initiation and propagation were observed by optical microscope and scanning electron microscope. The results showed that Al After 3 passes of Si alloy in A path, the crack appeared on the upper surface of the material (the surface contacting the inner corner of the mold). As the extrusion pass increases, the cumulative amount of strain accumulates continuously, and the crack increases from shallow To deep, change from small to large. The analysis shows that the material deforms sharply on the surface of ECAP during deformation. With the increase of extrusion pass, the brittle-hard phase eutectic Si is broken, and the broken eutectic Si deviates from the substrate ɑ -Al and appears with the pit , Brittle hard phase eutectic Si and holes at the stress concentration lead to crack initiation; cracks in the surface tensile stress and shear force to expand.