【摘要】：當(dāng)前,3C產(chǎn)品、航空航天、通訊電子等領(lǐng)域均面臨著日益增加的輕量化壓力,同時,一些零部件對材料的導(dǎo)熱性能往往有較高的要求(尤其是散熱器件),以保證和提高產(chǎn)品的壽命及工作穩(wěn)定性。純鎂的熱導(dǎo)率在常見商用金屬材料中僅次于銅和鋁,比熱導(dǎo)率與鋁相當(dāng);然而常用鑄造鎂合金的導(dǎo)熱性能卻明顯偏低,如AZ系鑄造鎂合金的熱導(dǎo)率僅為50 W(m·K)-1左右,這嚴(yán)重阻礙了鎂合金在有導(dǎo)熱性能需求的工程領(lǐng)域的應(yīng)用。因此,對鎂合金導(dǎo)熱性能研究并提高鎂合金導(dǎo)熱性能很有必要。本文以AZ91D鎂合金為對象,制備了不同成型工藝(半連續(xù)鑄造、壓鑄、擠壓)、熱處理工藝(T4、T6)和不同壓鑄厚度的鎂合金試樣。一方面,采用激光導(dǎo)熱儀測量所制備鎂合金試樣的熱導(dǎo)率,另一方面,通過光學(xué)顯微鏡(OM)、電子顯微鏡(SEM)、XRD、EDS等方法分析鎂合金試樣的微觀組織,從組織的角度,研究AZ91D鎂合金導(dǎo)熱性能的影響因素。本文主要研究結(jié)果及結(jié)論如下:(1)不同成型工藝下AZ91D鎂合金的熱導(dǎo)率有一定差異,壓鑄態(tài)AZ91D合金的熱導(dǎo)率高于半連續(xù)鑄造合金,擠壓變形使合金熱導(dǎo)率顯著降低。其主要機理有:1)半連續(xù)鑄造合金中包含較多發(fā)達的第二相,其固溶體中Al原子和Zn原子含量均較高且分布不均勻,使合金整體的熱導(dǎo)率降低;2)擠壓使合金產(chǎn)生大量晶界和內(nèi)部缺陷,同時大量Al原子固溶進Mg基體中,降低了合金熱導(dǎo)率。(2)固溶處理使半連續(xù)鑄造和壓鑄AZ91D合金的第二相充分溶解,大量Al原子固溶進Mg基體,破壞了Mg基體晶格排列的規(guī)則性,使合金熱導(dǎo)率降低;時效處理中,Al原子從Mg基體中析出并重新形成第二相,該過程消耗了Mg基體中的Al原子,從而熱導(dǎo)率增加。(3)對于擠壓態(tài)AZ91D合金,擠壓形成的位錯線在固溶處理中發(fā)生回復(fù),同時晶粒長大,組織中的缺陷減少,該過程有利于合金導(dǎo)熱性能,且其作用大于固溶體中Al含量增加對導(dǎo)熱性能的阻礙作用,使擠壓態(tài)合金固溶處理后的熱導(dǎo)率有所增加。經(jīng)時效處理后,一方面伴隨第二相析出,固溶體中Al含量減少,對合金導(dǎo)熱的阻礙減小,另一方面,時效處理使擠壓態(tài)合金晶粒粗化,晶界缺陷減少,有利于合金導(dǎo)熱的進行,因此合金熱導(dǎo)率上升。(4)隨著壓鑄厚度的減小,AZ91D合金內(nèi)部晶界增多,增加對電子和聲子的散射作用,合金熱導(dǎo)率隨之越低;另外隨著壓鑄厚度的減小,固溶于Mg基體的Al原子增多,對導(dǎo)熱不利,這與固溶處理對合金熱導(dǎo)率的影響趨勢一致。(5)溫度升高一方面使電子和聲子的運動能力增強,另一方面會引起缺陷熱阻減小并產(chǎn)生一定的時效行為,使AZ91D合金熱導(dǎo)率隨溫度升高而逐漸增大。
[Abstract]:At present, 3C products, aerospace, communication electronics and other fields are facing increasing lightweight pressure, at the same time, some parts often have higher thermal conductivity requirements (especially radiator parts). To ensure and improve the product life and work stability. The thermal conductivity of pure magnesium is second only to that of copper and aluminum in common commercial metal materials, and the specific thermal conductivity is equivalent to that of aluminum. However, the thermal conductivity of common cast magnesium alloys is obviously low. For example, the thermal conductivity of AZ cast magnesium alloys is only about 50 W (m K) -1, which seriously hinders the application of magnesium alloys in engineering fields with thermal conductivity requirements. Therefore, it is necessary to study and improve the thermal conductivity of magnesium alloys. In this paper, AZ91D magnesium alloy samples with different forming processes (semi-continuous casting, die-casting, extrusion), heat treatment (T4T6) and different die-casting thickness were prepared. On the one hand, the thermal conductivity of magnesium alloy samples was measured by laser thermal conductivity instrument. On the other hand, the microstructure of magnesium alloy samples was analyzed by means of optical microscope, (OM), electron microscope and (SEM), XRD,EDS. The factors affecting the thermal conductivity of AZ91D magnesium alloy were studied. The main results and conclusions of this paper are as follows: (1) the thermal conductivity of AZ91D magnesium alloy under different molding processes is different. The thermal conductivity of die-cast AZ91D alloy is higher than that of semi-continuous casting alloy. The main mechanisms are as follows: 1) there are more developed second phases in the semicontinuous casting alloys, and the content of Al atoms and Zn atoms in the solid solution is higher and the distribution is uneven, which reduces the overall thermal conductivity of the alloy; 2) extrusion causes a large number of grain boundaries and internal defects in the alloy, and a large number of Al atoms are dissolved into the Mg matrix, which reduces the thermal conductivity of the alloy. (2) the second phase of semi-continuous casting and die-casting AZ91D alloy is fully dissolved by solution treatment. A large number of Al atoms were dissolved into the Mg matrix, which destroyed the regularity of the lattice arrangement of the Mg matrix and reduced the thermal conductivity of the alloy. During aging treatment, Al atoms precipitate from the Mg matrix and reform the second phase, which consumes the Al atoms in the Mg matrix and increases the thermal conductivity. (3) for the extruded AZ91D alloy, The dislocation line formed by extrusion recovers during solution treatment, while the grain grows and the defects in the microstructure decrease. This process is beneficial to the thermal conductivity of the alloy, and the effect is greater than the effect of the increase of Al content in the solid solution on the thermal conductivity. The thermal conductivity of the extruded alloy increased after solution treatment. After aging treatment, on the one hand, with the precipitation of the second phase, the content of Al in the solid solution decreases and the hindrance to the thermal conductivity of the alloy decreases. On the other hand, the aging treatment results in the coarsening of the grain and the decrease of the grain boundary defect in the extruded alloy, which is beneficial to the thermal conductivity of the alloy. As a result, the thermal conductivity of AZ91D alloy increases. (4) with the decrease of die-casting thickness, the internal grain boundary of AZ91D alloy increases, and the scattering of electrons and phonons increases, the thermal conductivity of the alloy decreases with the decrease of die-casting thickness. In addition, with the decrease of die-casting thickness, the number of Al atoms dissolved in the Mg matrix increases, which is unfavorable to the thermal conductivity, which is consistent with the effect of solution treatment on the thermal conductivity of the alloy. (5) on the one hand, the increase of temperature increases the mobility of electrons and phonons. On the other hand, the thermal resistance of defects will decrease and a certain aging behavior will occur, and the thermal conductivity of AZ91D alloy will increase with the increase of temperature.
【學(xué)位授予單位】：重慶大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：TG146.22

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