【作者】 姜涛；

【导师】 许光明； 李勇；

【作者基本信息】 东北大学 ， 材料加工工程， 2022， 博士

【摘要】 Al-50Si合金具有密度低、耐磨性好、热导率高以及热膨胀系数低等优点,是一种理想的电子封装材料。目前,该类合金主要采用喷射沉积与粉末冶金方法制备。其中喷射沉积法制备工艺较为复杂,且后续需要通过致密化来提高沉积坯的致密度,生产成本较高。而粉末冶金方法因其制备的样品含氧量较高、易脏化,且当增强体含量较高时,合金的致密性较低。因此亟需开发一种新型低成本、高质量的高硅铝合金制备工艺以满足电子封装材料行业的发展需求。具有亚快速凝固特点的双辊铸轧技术将铸造和轧制工艺有机结合,可实现凝固与变形过程的同步进行。铸轧过程中金属的冷却速度可达200℃/s以上,显著细化了凝固组织,是一种制备电子封装用高硅铝合金材料的潜在理想技术。本研究首先采用熔铸法制备了 Al-50Si合金铸锭,研究了 P变质对铸态Al-50Si合金的作用机理,确定了铸态Al-50Si合金中Cu-14P变质剂的最佳含量。探究了 Al-50Si合金的熔体过热处理制度,研究了熔体过热处理对Al-50Si合金凝固组织及性能的影响。基于上述研究,探索出了细化Al-50Si合金中初晶Si的最佳工艺制度,并成功将其应用于铸轧实验,研究了铸轧速度与P变质对铸轧Al-50Si合金组织及性能的影响,获得了具有良好综合性能的铸轧Al-50Si合金板坯。本论文取得了如下研究成果:(1)研究了不同Cu-14P变质剂含量对铸态Al-50Si合金凝固组织及热膨胀性的影响。当Cu-14P变质剂含量为3 wt.%时,初晶硅的平均尺寸最小,为35.9μm,与未变质的合金相比,细化了 78.5%。由于初晶Si的细化导致合金中界面增多,抑制了α-Al膨胀,因此当变质剂含量为3 wt.%时,合金的平均热膨胀系数最小,为12.2×10-6/℃。当变质剂含量大于3 wt.%时,合金中AlP颗粒的聚集降低了细化效果,产生过变质。(2)将P变质工艺与熔体过热处理相结合,探究了不同过热度下合金的微观组织演变机制。由于高温熔体中AlP颗粒发生Ostwald熟化从而降低细化效率,因此将P变质与熔体过热处理相结合并不能提高变质剂的利用率,也不能进一步细化初晶Si。当变质剂含量为7 wt.%时,合金处于过变质状态,但Al2Cu相的产生使合金的宏观硬度达到峰值。(3)基于亚快速凝固薄带铸轧技术,建立了铸轧过程的温度场与流场的计算模型,并选取了 4 m/min、2.5 m/min与1 m/min作为Al-50Si合金的实验铸轧速度。模拟计算结果表明,随着铸轧速度增大,熔池出口处温度逐渐升高,并且熔池区内平均降温速率逐渐增大。当铸轧速度为4m/min时,平均降温速率为307.3℃/s,约为1 m/min时的3倍。(4)根据数值模拟结果,成功制备出了 Al-50Si合金铸轧板坯,阐明了铸轧凝固组织的特点,研究了不同铸轧速度对Al-50Si合金微观组织(初晶Si的形态和尺寸等)、宏观偏析行为以及Al基体的动态再结晶现象的影响。与传统铸造制备的合金相比,采用铸轧工艺制备的Al-50Si合金中初晶Si显著细化。当铸轧速度为1 m/min时,初晶Si的平均尺寸为40.6μm,与铸态合金相比,降低了 75.7%。铸轧速度增大,合金中初晶Si的平均尺寸逐渐减小。在铸轧Al-50Si合金中发现了 Al基体的动态再结晶现象,并且随着铸轧速度的增大,Al基体的再结晶程度逐渐提高。在铸轧合金中,初晶Si存在宏观中心偏析,而铸轧速度的提高可降低合金中初晶Si的中心偏析程度。(5)将P变质与铸轧工艺相结合,研究了 P变质对铸轧Al-50Si合金的微观组织及物理性能的影响。变质剂可进一步细化铸轧Al-50Si合金中的初晶Si,并改善初晶Si形貌。当Cu-14P变质剂含量为3 wt.%时,初晶Si的平均尺寸最小,为9.1μm。此时,铸轧合金具有最低的平均热膨胀系数与最高的室温热导率,分别为9.6×10-6/℃与103 W/(m·℃)。更多还原

【Abstract】 Al-50Si alloy which has advantages such as low density,excellent wear resistance,high thermal conductivity and low thermal expansion coefficient,is an ideal electronic packaging material.At present,such alloys are mainly prepared by spray deposition and powder metallurgy.The spray deposition technique is relatively complicated,and densification is required subsequently to improve the density of deposited blank,resulting in high preparation cost.The samples prepared by powder metallurgy are high in oxygen and prone to be polluted.In particular,the compactness of the alloy will be limited when the reinforcement contents are very high.Therefore,it is necessary to develop a low-cost high-silicon aluminum alloy by a high-quality preparation process to meet the needs for the electronic packaging industry.The twin-roll casting technique combines casting and hot rolling processes,possessing sub-rapid solidification characteristics.The solidification and deformation processes can be realized simultaneously in course of materials preparation.During the roll-casting process,the cooling rate of the metal can reach more than 200℃/s,which significantly refines the solidification structure,so that the roll-casting process is a potential technology in preparing high-silicon aluminum alloy materials for electronic packaging.In this study,the Al-50Si alloy ingots were first prepared by ingot metallurgy.The mechanism of P modification on the as-cast Al-50Si alloy was studied,and the optimum content of the Cu-14P modifier in the as-cast Al-50Si alloy was determined.The melt superheating treatment of Al-50Si alloy was investigated,and the effect of melt superheat treatment on the solidification microstructure and properties of Al-50Si alloy was studied.Finally,based on the above researches,the optimal refining method of primary Si in Al-50Si alloy was explored,and successfully applied to the roll-casting process.The effects of roll-casting speed and P modification on the microstructures and properties of cast-rolled Al-50Si alloy were studied,and roll-cast Al-50Si alloy slabs with good performance were obtained.The results were as follows:(1)The influence of different modifier contents on the microstructures and thermal expansion of the as-cast Al-50Si alloy was studied.When the content of Cu-14P modifier was 3 wt.%,the average size of primary Si was the smallest,which was 35.9μm,reduced by 78.5%compared with the unmodified state.The refinement of primary Si leads to the increase of the interface in the alloy,which inhibits the expansion of α-Al.Therefore,when the content of modifier was 3 wt.%,the average coefficient of thermal expansion of the alloy was the smallest,which was 12.2x10-6/℃.When the content of the modifier exceeded 3 wt.%,the AlP particles aggregation in the alloy occurred,causing over-modification.(2)The microstructure evolution of Al-50Si alloy with different degrees of superheating was studied by combining P modification process with melt superheating treatment.As the Ostwald ripening of AlP particles in the high temperature melt reduced refining efficiency,the combination of P modification and melt superheating treatment could neither improve the utilization rate of modifier,nor further refine the primary Si.The alloy was in the state of overmodification when the content of modifier was 7 wt.%,but the macro-hardness of alloy reached the peak value at this time due to the formation of Al2Cu phase.(3)The calculation model of the temperature and flow fields of the roll-casting process was established based on the sub-rapid solidification technology,and the roll-casting speed of 4 m/min,2.5 m/min and 1m/min were selected.According to the simulation results,the faster the roll-casting speed,the higher the temperature at the outlet of the molten pool and the greater the average cooling rate in the molten pool.When the roll-casting speed was 4 m/min,the average cooling rate was 307.3℃/s,which was about 3 times that of 1 m/min.(4)According to the numerical simulation results,the roll-cast Al-50Si alloy slab was prepared successfully and the microstructures of Al-50Si alloy at different roll-casting speeds were studied,including the morphology and size of primary Si,the macro-segregation behavior of alloy and the dynamic recrystallization of Al matrix.Compared with the traditional casting method,the primary Si in the roll-cast alloy could be refined.When the rolling speed was 1 m/min,the average size of primary Si was 40.6μm,showing a reduction of 75.7%compared with that of the as-cast alloy.The higher the rolling speed,the smaller the average size of primary Si in the alloy.Dynamic recrystallization of Al matrix was observed in roll-cast Al50Si alloy.The higher the roll-casting speed,the greater the degree of recrystallization of the Al matrix.There was central segregation of primary Si in roll-cast alloy,and the increase of roll-casting speed could improve the central segregation of primary Si.(5)The effect of P modification on the microstructures and physical performances of rollcast Al-50Si alloys were studied by combining P modification with twin-roll casting process.The primary Si could be further refined and the morphology of the primary Si could be improved by adding the modifier to the roll-cast Al-50Si alloy.When the content of modifier was 3 wt.%,the average size of primary Si reached the smallest,which was 9.1μm.At this time,the roll-cast samples had the lowest average coefficient of thermal expansion and the highest room-temperature thermal conductivity,which were 9.6×10-6/℃ and 103 W/(m·℃).更多还原