铜/钢爆炸焊接板浸铝铸件中铝/钢界面裂纹的形成与扩展

Crack initiation and propagation at Al/steel interface in castings produced by molten aluminum and explosively welded Cu/steel plate

采用铜/钢爆炸复合板浸铝铸造的方法制取了铝/钢铸件。用扫描电子显微镜对复合铸件中铝/钢界面裂纹的形成以及这些裂纹在不同热处理制度下和拉剪测试时的扩展形为进行了分析。研究表明,浸铝铸造后的裂纹主要存在于波侧面的Fe2Al5层中,且大部分平行于波形界面。当试样经过300～600℃,30min退火空冷后,裂纹从波侧面扩展到波谷和波峰,同时在波形界面的块状FeAl3相中也出现平行于波形界面的裂纹。铝和钢的热膨胀系数有较大差异,而在界面导致残余热应力是造成界面裂纹产生和扩展的主要原因。由于铝、钢接触反应时的Kirkendall效应使Fe2Al5层中产生较多的微孔,同时也由于该中间层较厚,因此微裂纹往往在该层中产生和扩展。拉剪测试后的断口分析表明材料主要沿铝/钢波形界面失效。

Al/steel bonding castings was manufactured by the molten aluminum and explosively welded Cu/steel plate. Crack initiation and propagation at Al/steel interface were investigated by SEM in the as-cast condition as well as in specimens which were heated at various temperatures and then air-cooled. The main cracks are found in the Fe_2Al_5 continuous intermetallic layer at the ridges of the wavy Al/steel interface and most of these cracks are parallel to the wavy interface. Being heated at different temperatures from 300 ℃ to 600 ℃, and then air-cooled, these cracks propagate from ridges to the vales and peaks, and also appear in FeAl_3 blocks as well. Most of these cracks are found to be parallel to the wavy interface too. The residual stress due to different thermal expansion coefficients of the interacting phases and the volume change effect associated with the formation of intermetallic compounds, is suggested to be responsible for the crack initiation. Kirkendall effects during the formation of Fe_2Al_5 result in amounts of tiny holes in this layer, which might facilitate the crack initiation and propagation afterwards.