原位颗粒增强ADC12铝基复合材料的制备及研究

发布时间：2018-03-05 23:17

  本文选题：超声　切入点：原位　出处：《南昌大学》2015年硕士论文　论文类型：学位论文

【摘要】：铝合金具有密度小、比强度高、成形性好、易于回收利用等优点,因而在国民经济中得到了较为广泛的应用。作为一种Al-Si-Cu系合金,ADC12因其优越的性能而被广泛应用于汽车工业领域。但是,合金组织中粗大的α-Al相和Si相却在一定程度上降低了材料的力学性能。而研究发现,一些原位增强相(如Al2O3、Al3Ti颗粒等)能够改善Al-Si合金组织,提高材料的各方面性能。故本文以Al-B2O3、Al-K2Ti F6、Al-Ti为反应体系,将高能超声处理技术与原位合成技术相结合,制备了原位(Al2O3、Al3Ti)颗粒增强ADC12铝基复合材料,力求利用超声产生的声空化效应和声流效应来细化颗粒,改善颗粒与熔体间的润湿性,迫使颗粒在熔体中均匀分散,从而提高复合材料的综合性能,使其能够更好的符合铝基复合材料的要求。另外,本文在以Al-K2TiF6为反应体系制备Al3Ti/ADC12复合材料的同时,还研究了电磁搅拌对其半固态浆料组织的影响,力求利用电磁搅拌作用于熔体时产生的强烈混合对流来改善晶体的结晶凝固过程,从而获得良好的复合材料半固态浆料。主要研究内容及结果如下:以Al-B2O3为反应体系,原位制备了Al2O3/ADC12复合材料。复合材料的微观组织研究表明:超声辅助下原位生成的Al2O3增强颗粒细小、圆整,在基体中分布也较为均匀;复合材料硅相组织与基体相比有了一定程度的改善,硅相形貌由原来的块状、长针状、板条状逐步转变为短棒状、颗粒状,其中未施加超声制备的复合材料组织中的硅相以短棒状为主,颗粒状较少,超声后复合材料组织中的短棒状硅相减少、且尺寸变得更为细小,颗粒状硅相则有所增加。复合材料的力学性能研究表明:经过超声处理的复合材料抗拉强度和延伸率比未施加超声的复合材料分别提高了13.5%和25.2%。以Al-K2TiF6为反应体系,采用熔体直接反应法,超声原位合成了Al3Ti/ADC12复合材料。研究表明:与常规原位反应相比,超声作用下反应更快、更彻底,且生成的Al3Ti增强颗粒形貌较规则、尺寸细小,平均尺寸约为1~2μm,在基体中分布也较为均匀。原位复合材料的铸态组织与基体相比均有所改善:α-Al相的轮廓变得愈加清晰,尺寸逐渐细化,形貌趋于圆整;Si相形貌则由原来的长针状、板条状逐步转变为短棒状、颗粒状。其中未施加超声制备的复合材料晶粒得到了一定的细化,Si相形貌以较大颗粒状为主,短棒状较少;二次超声条件下获得的复合材料晶粒得到了较大程度的细化,Si相形貌则变为了更加细小的颗粒状甚至纤维状。而经过超声处理的复合材料抗拉强度和伸长率分别达到255.2MPa和2.18%,比未施加超声的复合材料分别提高了19.4%和33.7%。复合材料的室温拉伸断口形貌分析表明:在超声作用下,复合材料断口上解理面变少,韧窝变小、变深、数量增多,表现为明显的韧性断裂。以Al-K2TiF6为反应体系,采用电磁搅拌法成功制备了原位Al3Ti/ADC12复合材料的半固态浆料,并研究了不同搅拌参数对该复合材料半固态组织的影响,揭示了半固态组织在电磁场作用下的演变机理。结果表明:在本实验降温搅拌过程中,随着搅拌时间的逐渐增加,复合材料半固态组织中的初生相形貌发生了多样性变化,经历了树枝状、蔷薇状、近球状的演变,其中在585℃时水淬取样的组织较佳,初生α-Al相主要呈近球状,弥散悬浮于液相中,平均尺寸约为35.2μm;在一定范围内,若固定相同的搅拌频率和搅拌时间,降温搅拌过程中随着搅拌电压的增大晶粒形貌趋于圆整,尺寸逐渐变小;若固定相同的搅拌电压和搅拌时间,降温搅拌过程中随着搅拌频率的增大晶粒先逐渐细化而后又逐渐增大。以Al-Ti为反应体系原位合成了Al3Ti/ADC12铝基复合材料。研究表明:对熔体施加机械搅拌后,复合材料组织中的Al3Ti颗粒相由原来的粘结、团聚慢慢变得分散开来,平均尺寸也有所减小;冷却方式的不同对复合材料中原位Al3Ti相的形貌也有较大的影响,在快速冷却的条件下,Al3Ti相的形貌为块状或颗粒状,而经缓慢冷却后,Al3Ti相的形貌却变为针状或板条状。对熔体施加超声后,复合材料组织中的Al3Ti相发生了较大的变化:若保持超声时间、超声频率及Ti的添加量不变,在一定范围内,随着超声功率的增加,Al3Ti颗粒尺寸变得越来越细小,分布也变得更加均匀;若保持超声功率、超声时间及超声频率不变,随着Ti含量的逐渐增加,Al3Ti颗粒会出现团聚和长大的现象;若保持超声功率、超声频率不变,随着超声时间的增加,超声效果会出现先加强后减弱的趋势。此外,原位Al3Ti/ADC12铝基复合材料的抗拉强度较基体合金而言有升高的趋势,并且复合材料的力学性能变化趋势与其组织变化趋势相一致,当Ti添加量为3%、超声功率为1.5kw、频率为20kHz、超声时间为6min时,其综合力学性能较好,抗拉强度为247.34MPa、延伸率为2.31%,比未施加超声的复合材料分别提高了21.3%和50.0%。而且,Ti的加入还能够细化基体组织中的α-Al相,使其由原来的粗大树枝状逐渐转变为细小枝晶状、蔷薇状甚至近球状。
[Abstract]:Aluminum Alloy has the advantages of low density, high specific strength, good formability, easy recycling and other advantages, so it has been widely used in the national economy. As a kind of Al-Si-Cu alloy, ADC12 because of its superior performance and is widely used in the field of automotive industry. However, the thick alloy of alpha -Al and the Si phase was reduced to a certain extent the mechanical properties of the materials. The study found that some in situ Reinforcement (such as Al2O3, Al3Ti particles) can improve the microstructure of Al-Si alloy, improve the properties of materials. This paper uses Al-B2O3, Al-K2Ti F6, Al-Ti reaction system, the high-energy ultrasound technique and in situ synthesis combined in situ preparation of (Al2O3, Al3Ti) ADC12 particles reinforced aluminum matrix composites, and strive to produce cavitation effect of the ultrasonic flow effect to fine particles, improve the wettability between particles and melt, forcing the particles Uniformly dispersed in the melt, thereby improving the performance of the composite materials, so that it can better meet the requirements of aluminum matrix composites. In addition, at the same time this system as the reaction system in Al-K2TiF6 Al3Ti/ADC12 composites, also studied the effect of electromagnetic stirring on the microstructure of the semi-solid slurry, stirring to strong mixed convection on the melt produced by electromagnetic crystal to improve the solidification process, so as to obtain good composite semi solid slurry. The main research contents and results are as follows: in the Al-B2O3 reaction system, Al2O3/ADC12 composite material was synthesized. The microstructure of the composites showed that the ultrasonic assisted Al2O3 in situ reinforced fine particles, round, distribution is more uniform in the matrix; composite silicon phase structure compared with the matrix has been improved to some extent, the Si morphology from the original block Long needle, lath, gradually transformed into short rod like particles, which does not apply, the microstructure of the composite ultrasonic preparation of silicon phase in the short rod, granular small, short rod shaped silicon composite tissue after ultrasound in phase decreased, and the size become smaller, granular silicon phase increased. Study on the mechanical properties of the composites show that the composite tensile strength and elongation of ultrasonic treatment than the composite without ultrasonic respectively increased by 13.5% and 25.2%. by Al-K2TiF6 reaction system, using the direct melt reaction method, ultrasonic in-situ Al3Ti/ADC12 composites were synthesized. The results show that: compared with conventional in situ reaction, the effects of ultrasound the reaction faster and more thoroughly, and the Al3Ti particles morphology was regular, the size is small, the average size is about 1~2 m, the distribution is more uniform in the matrix. The cast in situ composite materials Compared with the matrix organization are improved: a -Al phase profile becomes more and more clear, size gradually thinning, morphology tended to be round; Si morphology from long acicular lath gradually transformed into short rod, which is not applied. Granular material grain ultrasonic prepared to be refined, Si the morphology in large granular, short rod less; composite grains obtained two times under ultrasonic condition was refined obviously, the morphology of Si phase is changed to fine granular fibrous. Even after ultrasonic treatment of the composite tensile strength and elongation are 255.2MPa and 2.18% respectively, compared with the composite without applying ultrasound respectively improved 19.4% and the tensile fracture morphology of 33.7%. composite analysis shows that under the action of ultrasound, fracture of composite materials on the cleavage surface becomes less, dimple becomes small, dark, increase in the number of ,琛ㄧ幇涓烘槑鏄剧殑闊ф，

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