Sr变质Mg_(2)Si/Al-Cu-Si复合材料的机理与组织性能

Mechanism and Microstructure of Sr Metamorphic Mg_(2)Si/Al-Cu-Si Composites

采用熔炼法制备了x%Mg_(2)Si/Al-3%Cu-3%Si(x=15,20,25和30)复合材料,并选择15%和25%Mg_(2)Si含量的复合材料通过添加微量Sr进行了变质处理。结果表明,铸态复合材料组织由多边形块状Mg_(2)Si初生、棒状Mg_(2)Si共晶、网状θ-Al_(2)Cu、过剩Si和块状Q-(Al_(4)Cu_(2)Mg_(8)Si_(7))相组成。其中,Mg_(2)Si初生的晶粒尺寸约为31.2μm。随着Mg_(2)Si含量的增加,Mg_(2)Si初生由颗粒状转变为更为粗大的树枝状。加入0.04%Sr对15%Mg_(2)Si/Al-3%Cu-3%Si进行变质处理,Mg_(2)Si初生的晶粒尺寸减小至20.1μm,尖角状Mg_(2)Si初生转变为多边形。用第一性原理计算变质元素Sr在Mg_(2)Si中结合能和吸附能揭示Sr的变质机理。计算结果表明,Sr优先吸附在Mg_(2)Si晶体{111}面,固溶并取代晶格中的Mg原子,改变{100}晶面和{111}晶面的相对表面能,从而抑制Mg_(2)Si沿<100>晶相的生长速度,实现了Mg_(2)Si颗粒的细化。对15%和25%Mg_(2)Si/Al-3%Cu-3%Si复合材料及其变质态进行3点抗弯测试,结果表明,经过0.04%Sr变质的15%Mg_(2)Si/Al-3%Cu-3%Si复合材料抗弯强度和抗弯应变最高,分别达到246.9 MPa和1.23%。

In this paper, x%Mg_(2)Si/Al-3%Cu-3%Si (x=15, 20, 25 and 30, %) composites were prepared by smelting method. Firstly, the as-cast microstructures of the prepared materials were analyzed, and the results showed that the microstructures of the as-cast composites were composed of polygonal block Mg_(2)Si primary, rod-shaped Mg_(2)Si eutectic, netting θ-Al2Cu, residual Si and small block Q-(Al_(4)Cu_(2)Mg_(8)Si_(7)) phases. Among them, the size of Mg_(2)Si primary is 31.2 μm. Increasing of Mg_(2)Si content, Mg_(2)Si primary changes from angular polygon to coarse dendrite. The alloy of 15%Mg_(2)Si/Al-3%Cu-3%Si was modified by adding 0.04%Sr, the Mg_(2)Si primary size was reduced to 20.1 μm, and the angular polygon Mg_(2)Si primary was transformed into more rounded polygon. Using first principle to calculate binding energy and adsorption of the metamorphic element Sr in Mg_(2)Si revealed the metamorphic mechanism on Sr. The results show that Sr preferentially adsorbed on {111} plane of the Mg_(2)Si crystal, and dissolved in and replaced Mg atoms from original Mg_(2)Si crystal lattice. Therefore the relative surface energies of {100} and {111} crystal planes of unmodified Mg_(2)Si were changed. As a result, the growth of Mg_(2)Si along the <100> direction was inhibited and finally the refinement of Mg_(2)Si particles was realized. Three point bending tests were conducted on 15% and 25%Mg_(2)Si/Al-3%Cu-3%Si composites and their metamorphism. The results showed that the bending strength and the bending strain of 15%Mg_(2)Si/Al-3%Cu-3%Si composite metamorphized by 0.04%Sr were the highest, respectively reaching 246.9 MPa and 1.23%.