细晶Al-Si-Mg合金的组织遗传性与高屈服强度设计

Microstructure Heredity and High Yield Strength Design ofFine Grained Al-Si-Mg Alloys

常规Al-Si-Mg合金铸锭(如A356铸棒)晶粒异常粗大,重熔后导致铸件存在微观缩松、组织成分不均匀、合金性能较差等问题,因此有效控制其晶粒尺寸至关重要。将细晶A356铝合金重熔,研究其组织遗传性,并通过电子探针(EPMA)表征形核质点、差式扫描量热(DSC)分析其凝固过程,揭示了其遗传机理,且利用该细晶(A356铝合金)设计了高强度的Al-Si-Mg合金。研究结果表明,细晶A356铝合金重熔后仍为细晶组织,其平均晶粒尺寸为74.9μm。该种铝合金α-Al晶粒的中心处含有三元TiCB化合物粒子(TCB),合金重熔后即使经过长时间保温该粒子仍可稳定存在于熔体中,能够降低合金的形核过冷度,对α-Al起到形核作用,因此其细化效果得以保留,使细晶组织具有遗传性。此外,重熔后的细晶A356铝合金的抗拉强度为312.5 MPa,延伸率达到12.5%;在此基础上加入少量Mg以进一步提高其强度,设计得到的Al-Si-Mg合金的力学性能优异,特别是在延伸率为3.9%的情况下,Al-7Si-0.8Mg合金的抗拉强度和屈服强度分别高达386.4 MPa、352.9 MPa。

The grain size of conventional Al-Si-Mg alloy ingot(such as A356 cast ingot)is abnormally coarse,which leads to the casting defects of microstructure shrinkage and porosity,uneven structure composition and poor performance after remelting.Therefore,it is very important to control its grain size effectively.In this work,a fine grained A356 alloy was remelted and its microstructure heredity was studied.The Al-Si-Mg alloy with high strength was designed by using the fine grain A356 aluminum alloy.To reveal the correlative heredity mechanism,the nucleation particle of the fine grained A356 aluminum alloy was characterized by electron microprobe(EPMA),and the solidification process was analyzed by differential scanning calorimetry(DSC).The results showed that the average grain size of the fine grained A356 aluminum alloy was 74.9μm after remelting.It is found that theα-Al grains of the fine grained A356 aluminum alloy contains ternary compound TiCB particles(TCB).The particles are stable in the remelted A356 aluminum alloy,which are able to reduce the supercooling degree of the alloy.Therefore,even if remelted for a long time,it is qualified forα-Al nucleating and retain the high-efficiency refining effect.In addition,the tensile strength of the fine grain A356 aluminum alloy after remelting is 312.5 MPa,and the elongation reaches 12.5%.On this basis,a small amount of Mg was added to improve the strength.The designed Al-Si-Mg alloy has excellent mechanical property.The tensile strength and yield strength of Al-7Si-0.8Mg alloy are 386.4 MPa and 352.9 MPa,respectively,while the elongation remains at 3.9%.