熔体混溶与T6热处理对多元过共晶Al-18%Si合金组织和性能的影响
发布时间：2018-10-04 18:37
【摘要】：鉴于合金凝固行为、组织和性能显著地受其熔体状态的影响,以及我们过去的研究表明,采用经历熔体结构转变的高温熔体,与半固态的低温熔体混溶,能使二元铝硅合金中的初晶硅显著细化。本文在优化原混溶工艺的基础上,以多元过共晶铝硅合金(Al-18Si-1.5Cu-0.5Mg-0.5Mn-0.2Ti)为研究对象,系统研究了熔体混溶与Sr变质复合处理、T6热处理对合金组织形态和性能的影响,同时深入分析了诸种工艺的作用规律和机制。从挖掘材料潜能和工程实际应用的角度,为工业生产提供了工艺技术和基本原理方面的参考依据。主要结论如下:(1)常规铸造下,初晶硅多呈板块状和八面体形态,具有典型的小平面生长特征。合金经高低温熔体混溶与Sr变质复合处理后,初晶硅显著细化(晶粒尺寸细至10.27μm),且棱角钝化,表现出非小平面特征,共晶硅同时转变为珊瑚状。(2)对于高低温熔体混溶能够显著细化初晶硅,作者分析,主要得益于三方面:一,高温熔体热冲击半固态低温熔体,分解、产生了大量初晶硅的同质形核核心;二,熔体经历结构转变后,凝固形核过冷度增加,形核率显著增加;三,熔体经历结构转变后,系统自由能降低,硅晶体生长障碍增大,抑制了初晶硅的长大。而初晶硅棱角的钝化,主要是由于经历熔体结构转变的高温熔体促使了硅晶体生长界面发生了动力学粗糙化,从而使其生长界面由小平面向非小平面转变。(3)固溶处理过程中,共晶硅形貌发生了明显的改变,并显著影响着合金性能。固溶初期,共晶硅发生熔断和钝化,合金硬度得到提高;固溶中期,共晶硅球化且粒度适中,合金硬度达到峰值;固溶后期,共晶硅明显粗化,合金软化。(4)时效研究表明,随着时效温度的提高,合金硬化速率显著加快,但硬化能力不同,175℃时效处理时获得最佳硬度峰值。此外,在175℃和195℃下,时效曲线出现“双峰”现象,并结合脱溶DSC曲线,认为单、双峰现象与时效过程的序列析出有关,而GP区向亚稳相转变有明显时间间隔是产生双峰曲线的主要原因。最终确定合金最佳T6热处理工艺为:520℃固溶8h,175℃时效8h。(5)力学性能测试表明,合金经混溶处理后,布氏硬度、抗拉强度及延伸率分别提高11.0-14.0%、15.9-19.8%、55.7-58.9%,磨损量降低8.8-12.1%,分析认为主要与硅颗粒细化所产生的细晶强化,及硅颗粒固有断裂抗力的提高有关。而经T6热处理后,布氏硬度、抗拉强度分别提高32.4-36.0%、39.9-44.7%,磨损量降低21.6-25.4%,认为主要与沉淀相弥散析出所引起合金强度的提高有关。
[Abstract]:In view of the solidification behavior of the alloy, the microstructure and properties are significantly affected by its melt state, and our previous studies have shown that high temperature melts that undergo structural transformation of melts are mixed with semi-solid cryogenic melts. The primary silicon in binary Al-Si alloy can be refined obviously. Based on the optimization of the original miscibility process, the effects of melt miscibility and Sr modification on the microstructure and properties of multicomponent hypereutectic Al-Si alloy (Al-18Si-1.5Cu-0.5Mg-0.5Mn-0.2Ti) were studied systematically. At the same time, the action law and mechanism of various kinds of processes are analyzed in depth. From the point of view of excavating the potential of materials and practical application of engineering, this paper provides a reference for industrial production in terms of process technology and basic principle. The main conclusions are as follows: (1) under conventional casting, primary silicon is mostly plate-shaped and octahedral, with typical small plane growth characteristics. After high and low temperature melt miscibility and Sr modification, the primary silicon is refined (grain size up to 10.27 渭 m), and angular passivation), showing non-small plane characteristics. At the same time, eutectic silicon is transformed into coralline. (2) for high and low temperature melt miscibility, primary silicon can be significantly refined. The author analyses that the main benefits are as follows: first, high temperature melt heat shock semi-solid low temperature melt, decompose, decompose, A large number of homogenous nucleation cores of primary silicon were produced; second, the supercooling degree of solidification nucleation increased and the nucleation rate increased significantly after the melt experienced structural transformation; third, after the melt experienced structural transformation, the free energy of the system decreased and the growth barrier of silicon crystal increased. The growth of primary silicon was inhibited. The passivation of the prism angle of primary silicon is mainly due to the high temperature melt undergoing melt structure transformation, which results in the dynamic coarsening of the growth interface of silicon crystal, which makes the growth interface of silicon crystal change from Xiaoping to non-small plane. (3) in the process of solution treatment, The morphology of eutectic silicon has changed obviously and the properties of the alloy have been greatly affected. In the early stage of solution, eutectic silicon was melted and passivated, and the hardness of eutectic silicon was improved. In the middle stage of solution, eutectic silicon spheroidized and its particle size was moderate, and the hardness of eutectic silicon reached its peak. At the later stage of solution, eutectic silicon became coarser and alloy softened. (4) Aging study showed that, With the increase of aging temperature, the hardening rate of the alloy accelerates significantly, but the best hardness peak value is obtained when the hardening ability is different at 175 鈩，
本文编号：2251449
[Abstract]:In view of the solidification behavior of the alloy, the microstructure and properties are significantly affected by its melt state, and our previous studies have shown that high temperature melts that undergo structural transformation of melts are mixed with semi-solid cryogenic melts. The primary silicon in binary Al-Si alloy can be refined obviously. Based on the optimization of the original miscibility process, the effects of melt miscibility and Sr modification on the microstructure and properties of multicomponent hypereutectic Al-Si alloy (Al-18Si-1.5Cu-0.5Mg-0.5Mn-0.2Ti) were studied systematically. At the same time, the action law and mechanism of various kinds of processes are analyzed in depth. From the point of view of excavating the potential of materials and practical application of engineering, this paper provides a reference for industrial production in terms of process technology and basic principle. The main conclusions are as follows: (1) under conventional casting, primary silicon is mostly plate-shaped and octahedral, with typical small plane growth characteristics. After high and low temperature melt miscibility and Sr modification, the primary silicon is refined (grain size up to 10.27 渭 m), and angular passivation), showing non-small plane characteristics. At the same time, eutectic silicon is transformed into coralline. (2) for high and low temperature melt miscibility, primary silicon can be significantly refined. The author analyses that the main benefits are as follows: first, high temperature melt heat shock semi-solid low temperature melt, decompose, decompose, A large number of homogenous nucleation cores of primary silicon were produced; second, the supercooling degree of solidification nucleation increased and the nucleation rate increased significantly after the melt experienced structural transformation; third, after the melt experienced structural transformation, the free energy of the system decreased and the growth barrier of silicon crystal increased. The growth of primary silicon was inhibited. The passivation of the prism angle of primary silicon is mainly due to the high temperature melt undergoing melt structure transformation, which results in the dynamic coarsening of the growth interface of silicon crystal, which makes the growth interface of silicon crystal change from Xiaoping to non-small plane. (3) in the process of solution treatment, The morphology of eutectic silicon has changed obviously and the properties of the alloy have been greatly affected. In the early stage of solution, eutectic silicon was melted and passivated, and the hardness of eutectic silicon was improved. In the middle stage of solution, eutectic silicon spheroidized and its particle size was moderate, and the hardness of eutectic silicon reached its peak. At the later stage of solution, eutectic silicon became coarser and alloy softened. (4) Aging study showed that, With the increase of aging temperature, the hardening rate of the alloy accelerates significantly, but the best hardness peak value is obtained when the hardening ability is different at 175 鈩，
本文编号：2251449
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