Al-5Ti-0.2C细化剂对7085铝合金形核及过冷度的影响

Effect of Al-5Ti-0.2C refiner on nucleation and undercooling degree of 7085 aluminum alloy

在7085铝合金凝固过程中添加不同质量分数的Al-5Ti-0.2C细化剂,对比其铸锭凝固组织,并用DSC测定其凝固过程熔体过冷度,探讨Al-5Ti-0.2C细化剂对铝熔体形核与过冷度的影响。研究结果表明:Al-5Ti-0.2C细化剂能够明显细化晶粒,当细化剂质量分数为0.5%时细化效果最好;细化剂质量分数的差异对DSC曲线中的熔化曲线影响较小,而凝固曲线有明显差异;在凝固过程中增大细化剂质量分数,铝熔体形核过冷度与最大过冷度都呈递减趋势,当细化剂质量分数超过0.5%时,过冷度不再有明显递减趋势;Ti C颗粒是铝熔体异质形核的核心,凝固过程中Ti C颗粒的发生团聚,从而增大形核基底颗粒粒度,减小润湿角与临界形核能,最终减小熔体中形核所需过冷度。

Different mass fractions of Al-5Ti-0.2C refiner were added during the solidification of 7085 aluminum alloy, the microstructures of ingots with different mass fractions of Al-5Ti-0.2C refiner were compared, and DSC was used to measure the undercooling degree of the melt during solidification. The effects of Al-5Ti-0.2C refiner on nucleation and undercooling degree during the solidification of 7085 aluminum alloy were investigated. The results show that the microstructure is refined with Al-5Ti-0.2C refiner and 0.5% mass fraction of refiner can achieve the best performance. The melting curves are not influenced by the change of mass fraction of refiner, while the cooling curves make some difference： the nucleation undercooling degree and maximum undercooling degree of the melt both decrease with the increase of mass fraction of Al-5Ti-0.2C refiner but decrease little when the mass fraction is over 0.5%. TiC particles are the nucleants of heterogeneous nucleation, and these particles will gather to increase the substrate size, which decreases the contact angle and the critical nucleation energy and decreases the undercooling degree needed for nucleation in the end.