采用拉伸性能测试、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、深腐蚀、定量金相等技术手段研究了铝铜合金中富铁相对合金力学性能及拉伸断裂行为的影响.结果表明:随着Mn含量的增大,高铁含量合金力学性能得到改善,这主要是由于富铁相的演变和T相的增多以及铸造缺陷减少有关.针状β-Fe是铝铜合金中危害最大的富铁相.在拉伸过程中,针状β-Fe容易引起应力集中,从而导致富铁相与α(Al)基体界面断裂失效.同时针状β-Fe作为裂纹的起源,裂纹将沿着纵向发生二次扩展.与针状β-Fe相比,汉字状的富铁相对性能危害性更小,这是由于裂纹将在汉字状的Alm Fe和α-Fe中的枝晶臂间产生偏转,从而有效阻止裂纹的扩展.与AlmFe相比,α-Fe比Alm Fe危害更小.这主要是由于AlmFe具有晶体缺陷,本身能承受拉应力更小,枝晶发达的α-Fe与铝基体的结合力更大,同时发达的枝晶臂可以更加有效抑制裂纹的扩展.
The effect of iron-rich intermetallics on tensile fracture behavior of Al-Cu cast alloys with different Mn contents was studied by tensile test,scanning electron microscopy (SEM),transmission electron microscopy (TEM),deep etching technique and image analysis.The tensile properties of Al-Cu alloys containing high Fe content were improved with Mn increasing,which was attributed to the evolution of iron-rich intermetallics,the increase of T phases and the decrease of cast defects.During tensile deformation,the needle-like β-Fe resulted in stress concentration easily and the failure mainly appeared at iron-rich intermetallic particle/Al matrix interfaces.The needle-like β-Fe acted as crack initiation sites,and the second crack was easier to initiate and propagate along the longitudinal direction.The Chinese script intermetallic was less damaged to the tensile properties compared to the needle-like β-Fe,because the cracks were usually deflected along the branches/arms of the Chinese script iron-rich intermetallic,making alloys more resistant to crack propagation during tensile deformation.The Chinese script α-Fe was less damaged to the tensile properties compared to the Chinese script AlmFe.The reason was that AlmFe had crystal defects which endured much less tensile stress.The developed dendrite for α-Fe led to tighter cohesion between α-Fe and α(Al) matrix,and made the cracks difficult to propagate.
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