某铝型材挤压模具在服役期间发生开裂。采用宏观观察、化学成分分析、硬度测试、非金属夹杂物评定、金相检验和扫描电镜分析等方法对模具开裂的原因进行分析。结果表明:电火花加工的工艺参数选择不当,使模具型腔表面产生很厚的白亮层,并伴有微裂纹,微裂纹延伸至热影响区,破坏了材料的连续性,降低了模具的耐疲劳性能;加工过程中尖端部位产生应力集中,在挤压力和热应力的作用下,裂纹不断萌生并扩展,最终导致模具发生开裂。

The aluminum profile extrusion mold cracked during service. Macroscopic observation, chemical composition analysis, hardness test, non-metallic inclusion evaluation, metallographic examination and scanning electron microscopy analysis were used to analyze the causes of mold cracking. The results show that the improper selection of electrical discharge machining process parameters resulted in a thick white layer on the surface of the mold cavity, accompanied by microcracks, which extended to the heat affected zone, destroyed the material continuity and reduced the fatigue resistance of the mold. During the machining process, there was stress concentration at the tip. Under the action of extrusion pressure and thermal stress, cracks continuously initiated and expanded, ultimately led to mold cracking.