学术论文

      7050铝合金半连铸过程应力场及开裂倾向

      Stress field and cracking tendency of AA7050 alloy during direct-chill casting

      摘要:
      7050铝合金在半连铸生产过程中发生热裂和冷裂的倾向很高,不但影响了产品的质量和生产效率,还可能导致生产事故。工厂常采用试错法以找到最优的工艺参数,但这种方法成本高且效率低。运用数值模拟的方法再现铸造过程中各物理场的变化情况,已成为优化铝合金熔铸工艺非常重要的研究手段。本文通过将温度场、流场和应力场进行直接耦合,对7050铝合金的半连铸过程进行了数值模拟研究。结果显示,在糊状区沿铸锭宽度方向的应力和应变分量最大,特别是在起始铸造阶段,因而最容易在起始阶段产生垂直于宽度方向的热裂纹。冷裂与铸锭内应力集中有关,根据计算可知铸锭在冷却至200℃时冷裂倾向最大。由实际裂纹所处的部位及所需的临界尺寸可以推测,该冷裂纹极有可能是糊状区产生的热裂纹在低温时失稳扩展而形成的。
      Abstract:
      AA7050 alloy has a very high hot tearing and cold cracking tendency during direct-chill casting, which can affect its product quality and productivity, even cause industrial accidents. The trial and error method is often used in a foundry factory to find the optimum process parameters. However, this kind of approach is very costly and inefficient. Numerical modeling can reproduce the evolution of multi-physical fields in direct-chill casting, and it has been proved to be an indispensable tool in improving the casting process of aluminum alloys. In this paper, a direct-chill casting process of AA7050 alloy was simulated through direct coupling of ther-mal, fluid flow and stress fields. Simulation results showed that in the mushy zone the largest stress and strain components could be observed in the width direction, especially at the start-up phase. As a result, hot tearing perpendicular to the width direction was most likely to occur at this stage. The formation of cold cracking was closely related to stress concentration in the ingot, and the highest cold cracking tendency can be seen when the ingot was cooled to 200 ℃ . According to the position of the cold crack in the ingot and the critical crack size needed, a speculation could be made that the cold crack was possibly caused by the further propagation of hot tearing at lower temperatures.
      Author: BAI Qing-ling LI Hong-xiang ZHANG Ji-shan ZHUANG Lin-zhong
      作者单位: 北京科技大学新金属材料国家重点实验室,北京,100083
      刊 名: 北京科技大学学报 ISTICEIPKU
      年,卷(期): 2014, (11)
      分类号: TG292
      机标分类号: TP3 TG2
      在线出版日期: 2014年12月11日
      基金项目: 北京实验室建设项目,中央高校基本科研业务费专项资金资助项目,教育部博士学科点专项科研基金资助项目,新金属材料国家重点实验室开放课题资助项目