Effects of Cu addition on microstructure and mechanical properties of Er-modified Al-10Mg₂Si cast alloys

Abstract

The solidification microstructure and mechanical properties of hypoeutectic Al-10Mg₂Si cast alloys with different Cu contents and 0.45 wt.% Er were investigated using an optical microscope, scanning electron microscope, and an electronic universal testing machine. Results showed that Cu and Er could significantly reduce the grain size of the eutectic Mg₂Si phase from 15.4 µm for the base alloy to 5.8 µm for the alloy with 1.5 wt.% Cu and 0.45 wt.% Er. Meanwhile, the needle-like β-Al₅FeSi phase was modified to fine sized irregular shaped Cu, Er and Fe-rich particles with the additions of Cu and Er. The strength and ductility of the Al-10Mg₂Si as-cast alloys were simultaneously improved by the additions of Cu and Er, and the ultimate tensile strength, yield strength and elongation increase from 223 MPa, 136 MPa and 2.1% to 337 MPa, 169 MPa and 4.7%, respectively. The heterogeneous nucleation of Mg₂Si on AlP was avoided by forming Cu, Er and P-containing phases, due to the additions of Cu and Er. Moreover, the Cu and Er atomic clusters and their intermetallic segregated on the surface of the eutectic Mg₂Si and inhibited the growth of the eutectic Mg₂Si, which were responsible for the modification of the eutectic Mg₂Si.

摘要

本文采用X射线衍射仪、 光学显微镜、 扫描电镜(附加能谱仪)和电子万能试验机等研究了不同Cu含量Er变质亚共晶Al-10Mg₂Si铸造合金的凝固组织和力学性能. 结果表明, Cu和Er能显著降低共晶Mg₂Si相的晶粒尺寸, 从基础合金的15.4 μm减小到含1.5 wt.%Cu和0.45 wt.%Er合金的5.8 μm, 并使其结构从粗板状和汉字状转变为细珊瑚状和纤维状. 同时, 通过添加Cu和Er, 将针状β-Al₅FeSi相改变为细小的不规则形状的富Cu、 Er和Fe颗粒. Cu和Er的加入同时提高了Al-10Mg₂Si 铸态合金的强度和塑性, 抗拉强度、 屈服强度和伸长率分别从223 MPa、 136 MPa和2.1%提高到337 MPa、 169 MPa 和4.7%. 由于Cu和Er的加入, 共晶Mg₂Si在AlP上形成富Cu、 Er和P相, 避免了其在AlP上的异相成核. 此外, 在共晶Mg₂Si表面和相邻两个Mg₂Si晶粒之间的Cu、 Er原子团簇及其金属间化合物抑制了共晶Mg₂Si的生长, 这是Mg₂Si变质效果良好的原因.