本文關(guān)鍵詞：納米SiC顆粒增強(qiáng)Mg-9Al-lSi復(fù)合材料的ECAP變形組織及高溫蠕變行為研究　出處：《太原理工大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： Mg-Al-Si復(fù)合材料 納米SiC顆粒 等通道轉(zhuǎn)角擠壓 顯微組織 高溫蠕變行為

【摘要】：高溫穩(wěn)定相Mg_2Si增強(qiáng)Mg-Al-Si復(fù)合材料是最早為汽車動(dòng)力系統(tǒng)量身打造的抗蠕變鎂基復(fù)合材料。然而,鑄態(tài)Mg-Al-Si復(fù)合材料中網(wǎng)狀Mg17Al12相和粗大漢字狀Mg_2Si相會(huì)嚴(yán)重割裂基體,導(dǎo)致力學(xué)性能大幅降低,限制了其廣泛應(yīng)用。因此,改善第二相的尺寸和形貌對(duì)Mg-Al-Si復(fù)合材料性能的提高有重要意義。本文通過半固態(tài)攪拌+超聲波分散技術(shù)制備了納米SiC顆粒含量為1wt.%的Mg-9Al-1Si(記為Mg-9Al-1Si-1SiC)復(fù)合材料,并對(duì)復(fù)合材料進(jìn)行ECAP變形。采用OM、SEM、XRD、EDS和TEM等檢測手段,分析了納米SiC顆粒對(duì)Mg-9Al-1Si復(fù)合材料組織的影響,以及固溶態(tài)Mg-9Al-1Si-1SiC復(fù)合材料不同道次變形后顯微組織的變化規(guī)律;并對(duì)復(fù)合材料的室溫力學(xué)性能和高溫蠕變性能進(jìn)行了系統(tǒng)研究。研究結(jié)果發(fā)現(xiàn),鑄態(tài)的Mg-9Al-1Si復(fù)合材料中添加1wt.%納米SiC顆粒之后,基體晶粒、Mg17A112和Mg_2Si相都得到了明顯細(xì)化,但Mg17A112相仍然呈網(wǎng)狀分布,Mg_2Si相仍然呈漢字狀形態(tài);納米SiC顆粒在基體中分布較為均勻,而在Mg17Al12和Mg_2Si相周圍呈團(tuán)簇分布。對(duì)鑄態(tài)Mg-9Al-1Si和Mg-9Al-1Si-1SiC復(fù)合材料直接進(jìn)行4道次ECAP變形,基體晶粒顯著細(xì)化,Mg17Al12和Mg_2Si相明顯破碎。與擠壓態(tài)Mg-9Al-1Si復(fù)合材料相比,擠壓態(tài)Mg-9Al-1Si-1SiC復(fù)合材料的基體晶粒更加細(xì)小,碎化的Mg17Al12和Mg_2Si顆粒較小且分布更加均勻;另外ECAP變形后,納米SiC顆粒分布得到改善,使其表現(xiàn)出較高的力學(xué)性能。然而,鑄態(tài)Mg-9Al-1Si-1SiC復(fù)合材料直接ECAP變形后,組織中仍然存在少量尺寸較大的塊狀Mg17Al12相,在室溫拉伸過程中,塊狀Mg17Al12相附近容易造成應(yīng)力集中,成為微裂紋萌生的根源,將會(huì)阻礙力學(xué)性能的進(jìn)一步提高。在擠壓之前對(duì)Mg-9Al-1Si-1SiC復(fù)合材料進(jìn)行固溶處理來消除Mg17Al12相,再對(duì)固溶態(tài)Mg-9Al-1Si-1SiC復(fù)合材料進(jìn)行不同道次ECAP變形發(fā)現(xiàn):不同道次變形后析出的Mg17Al12均為細(xì)小的顆粒狀,2道次變形后析出的Mg17Al12顆粒的數(shù)量最多;隨著變形道次增加,Mg_2Si相逐漸碎化且分布更加均勻;基體的平均晶粒尺寸在2道次變形后最小。復(fù)合材料的抗拉強(qiáng)度和伸長率隨著變形道次增加而逐漸升高,4道次變形后分別為296MPa和8.8%;而屈服強(qiáng)度在2道次變形后最高,4道次變形后有所降低。在473K/70MPa蠕變條件下,鑄態(tài)Mg-9Al-1Si-1SiC復(fù)合材料抗蠕變性能高于鑄態(tài)Mg-9Al-1Si復(fù)合材料;而對(duì)于擠壓態(tài)Mg-9Al-1Si-1SiC復(fù)合材料,其抗蠕變性能明顯低于鑄態(tài)復(fù)合材料,并且晶粒尺寸越小,穩(wěn)態(tài)蠕變速率越高,抗蠕變性能越差。在(448～498K)/(70～90MPa)的蠕變條件下,鑄態(tài)Mg-9Al-1Si-1SiC復(fù)合材料的應(yīng)力指數(shù)為5.51～6.89,蠕變激活能為86～111kJ/mol,蠕變機(jī)制為受擴(kuò)散控制的位錯(cuò)攀移機(jī)制和第二相顆粒增強(qiáng)機(jī)制的共同作用。
[Abstract]:High-temperature stable phase Mg_2Si reinforced Mg-Al-Si composites are the first creep resistant magnesium matrix composites designed for automotive power systems. The network Mg17Al12 phase and the coarse Chinese character Mg_2Si phase in the as-cast Mg-Al-Si composites will seriously split the matrix, which leads to a significant reduction in mechanical properties, which limits its wide application. It is important to improve the size and morphology of the second phase for improving the properties of Mg-Al-Si composites. In this paper, semi-solid stirring is used to improve the properties of Mg-Al-Si composites. Mg-9Al-1Si with the content of 1wt.% SiC nanoparticles was prepared by ultrasonic dispersion technique. It is described as Mg-9Al-1Si-1Si-1SiC) composite material. The composite materials were deformed by ECAP. The methods of OMSEMXRDX DS and TEM were used. The effect of nanometer SiC particles on the microstructure of Mg-9Al-1Si composites was analyzed. And the change of microstructure of solid solution Mg-9Al-1Si-1SiC composites after different pass deformation; The mechanical properties of the composites at room temperature and creep properties at high temperature were systematically studied. The results showed that after adding 1wt.% SiC particles into the as-cast Mg-9Al-1Si composites. The matrix grains of Mg17A112 and Mg_2Si phase were refined obviously, but the Mg17A112 phase was still distributed in the form of network, and the phase of mg _ 2Si was still in the shape of Chinese characters. The distribution of SiC nanoparticles in the matrix is more uniform. The as-cast Mg-9Al-1Si and Mg-9Al-1Si-1SiC composites were directly ECAP for 4 times. Deformation. The matrix grains were significantly refined and the Mg17Al12 and Mg_2Si phases were obviously broken, compared with the extruded Mg-9Al-1Si composites. The matrix grains of extruded Mg-9Al-1Si-1SiC composites are smaller and the particles of Mg17Al12 and Mg_2Si are smaller and more evenly distributed. In addition, after the deformation of ECAP, the distribution of SiC nanoparticles was improved, which resulted in higher mechanical properties. After direct ECAP deformation of the as-cast Mg-9Al-1Si-1SiC composites, a small number of larger bulk Mg17Al12 phases still exist in the microstructure, and during the tensile process at room temperature. It is easy to cause stress concentration near the block Mg17Al12 phase, which is the root of microcrack initiation. It will hinder the further improvement of mechanical properties. The Mg-9Al-1Si-1SiC composites were treated with solid solution before extrusion to eliminate the Mg17Al12 phase. The results of ECAP deformation showed that the Mg17Al12 precipitated after the different passes were fine granular. The number of Mg17Al12 particles precipitated after the second pass deformation is the highest; With the increase of deformation pass, the Mg2Si phase is gradually broken and distributed more evenly. The average grain size of the matrix is the smallest after two times of deformation. The tensile strength and elongation of the composites increase gradually with the increase of the number of the deformation passes. After 4 times of deformation, the tensile strength and elongation of the composites are 296MPa and 8.8, respectively. However, the yield strength decreases after the maximum of 4 passes after two passes of deformation, and the creep condition of 473K / 70 MPA is the same as that under the condition of 473K / 70MPa. The creep resistance of as-cast Mg-9Al-1Si-1SiC composites is higher than that of as-cast Mg-9Al-1Si composites. However, the creep resistance of extruded Mg-9Al-1Si-1SiC composites is obviously lower than that of as-cast composites, and the smaller the grain size, the higher the steady creep rate. The worse the creep resistance is, the worse the creep property is under the creep condition of 448 / 498KT / 70 / 90MPa. The stress index of as-cast Mg-9Al-1Si-1SiC composites is 5.51kJ / mol and the creep activation energy is 86111kJ / mol. The creep mechanism is the joint action of dislocation climbing mechanism controlled by diffusion and the second phase particle enhancement mechanism.
【學(xué)位授予單位】：太原理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TB333

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