Sr和Y添加对A356铝合金显微组织和力学性能的影响及机理

Effect of Sr and Y Addition on Microstructure and Mechanical Properties of A356 Aluminum Alloy and Its Mechanism

摘要:

通过金相显微镜、扫描电镜、透射电镜观察，能谱分析以及力学性能实验，研究了添加Sr和Y对A356铝合金显微组织和力学性能的影响。结果表明，相比于单加Sr或Y，复合添加Sr和Y时，共晶Si由板片状或针状完全转变为纤维状，α-Al的等效晶粒直径从42.49 μm减小至26.63 μm，二次枝晶臂间距从22.38 μm减小至13.60 μm，抗拉强度从166.1 MPa增加到185.3 MPa，延伸率从3.6%提高至7.6%，断裂方式也从脆性断裂转变为韧脆型断裂。探讨了Sr和Y复合添加时的细化机理和变质机理，得出α-Al晶粒细化的主要原因是α-Al以Al₃Y为基底进行快速非均质形核，变质机理为杂质诱导孪晶并以孪晶凹谷机制进行生长。

Abstract:

The effects of Sr and Y addition on the microstructure and mechanical properties of A356 aluminum alloy were studied by metallographic microscope, scanning electron microscope, transmission electron microscope, energy dispersive spectra and mechanical property tests. The results show that the combined addition of Sr and Y can obtain the best microstructure and mechanical properties compared with the separate addition of Sr or Y. The eutectic Si changes completely from flake-like or acicular-like to fibrous shape, the equivalent grain diameter of α-Al decreases from 42.49 μm to 26.63 μm, the secondary dendrite arms spacing (SDAS) decreases from 22.38 μm to 13.60 μm, the tensile strength increases from 166.1 MPa to 185.3 MPa, the elongation increases from 3.6% to 7.6%, and the fracture mode changes from brittle fracture to ductile-brittle fracture. The refinement mechanism and modification mechanism of Sr and Y were discussed. It is concluded that the main reason for α-Al grain refinement is the rapid heterogeneous nucleation of α-Al based on Al₃Y, and the modification mechanism is impurity-induced twins which grow in the mechanism of twin plane reentrant edge.