本文選題：活塞 + 鋁硅合金��； 參考：《西安工業(yè)大學(xué)》2017年碩士論文

【摘要】：活塞長期工作在高溫高壓的惡劣環(huán)境中,承受著極高的周期性熱機(jī)耦合疲勞載荷,活塞合金中粗大的形狀不規(guī)則的初生硅和共晶硅是高周疲勞裂紋萌生的主要源頭,研究Si相的細(xì)化方法是提升活塞合金綜合性能的有效途徑。本文分別研究了Si含量、稀土元素Nd、混合稀土La-Ce和超聲場對活塞用Al-Si-Cu-Mg-Ni系合金的組織演變和力學(xué)性能的影響。通過光學(xué)顯微鏡(OM)、掃描電子顯微鏡(SEM)等儀器,分析了上述因素對該合金凝固過程中析出相的形貌和分布的影響。并用電子萬能試驗(yàn)機(jī)對其力學(xué)性能進(jìn)行了測試研究。確定了稀土的最佳添加量,也確定了超聲的最佳超聲功率和超聲溫度。主要的研究成果如下:(1)隨著Si含量的增加,活塞合金的熱膨脹系數(shù)在減小,其流動(dòng)性在增加,合金顯微組織中初生Si的等積圓直徑和所占的面積分?jǐn)?shù)都在增加,合金的高溫抗拉強(qiáng)度(350℃、425℃)和延伸率都在減小。(2)當(dāng)Nd含量≤0.3%時(shí),α-Al基體得以細(xì)化。在Nd含量為0.3%時(shí),初生硅的等積圓直徑和未添加Nd時(shí)的相比,減小了73%,共晶硅明顯細(xì)化。當(dāng)Nd含量增加至0.8%及以上時(shí),合金中出現(xiàn)了富稀土相,其力學(xué)性能顯著降低。Nd含量為0.3%時(shí)合金的350℃抗拉強(qiáng)度較未添加Nd時(shí)提高了29.8%。Nd元素聚集在AlCuNi相周圍,造成了成分過冷,抑制了AlCuNi相的長大,AlCuNi相由粗大的骨骼狀轉(zhuǎn)變?yōu)榧?xì)小的棒狀。(3)混合稀土La-Ce對鋁硅合金中的Si相具有良好的變質(zhì)效果。當(dāng)混合稀土La-Ce含量為0.5%時(shí),初生Si的等積圓直徑和共晶Si的平均長度均最小,分別為16.7μm和22.12μm。但是混合稀土加入量超過0.5%時(shí),會(huì)產(chǎn)生一種長針狀的富稀土相,這種富稀土相的出現(xiàn),會(huì)嚴(yán)重?fù)p害活塞合金的力學(xué)性能。當(dāng)混合稀土La-Ce添加含量為0.35%時(shí),合金的室溫抗拉強(qiáng)度和350℃抗拉強(qiáng)度均達(dá)到最大值,分別為318MPa和124MPa,較未添加混合稀土?xí)r,分別增加了10.0%和30.5%。(4)超聲場促進(jìn)了鋁硅合金內(nèi)等軸狀晶粒的形成,細(xì)化了初生Si、共晶Si。在處理溫度為720℃,超聲功率為0~1400W處理?xiàng)l件下,初生Si的平均等積圓直徑從40.73μm減小到23.35μm;共晶Si的平均長度從39.6μm減小到27.1μm;其他第二相的形態(tài)未發(fā)生改變;合金的室溫抗拉強(qiáng)度和350℃抗拉強(qiáng)度比未超聲時(shí)分別提高了21.9%和22.8%。熔體超聲處理細(xì)化了硅相,提升了合金性能。
[Abstract]:The piston works in the harsh environment of high temperature and high pressure for a long time and bears extremely high cyclic thermo-mechanical coupling fatigue load. The coarse and irregular primary silicon and eutectic silicon in the piston alloy are the main source of high cycle fatigue crack initiation. It is an effective way to improve the comprehensive properties of piston alloy by studying the refining method of Si phase. The effects of Si content, rare earth element ND, mixed rare earth La-Ce and ultrasonic field on the microstructure evolution and mechanical properties of Al-Si-Cu-Mg-Ni series alloy for piston were studied in this paper. The influence of the above factors on the morphology and distribution of precipitated phases in the solidification process of the alloy was analyzed by means of optical microscope and scanning electron microscope (SEM). The mechanical properties are tested and studied by electronic universal testing machine. The optimum addition amount of rare earth, the optimum ultrasonic power and ultrasonic temperature were also determined. The main results are as follows: (1) with the increase of Si content, the coefficient of thermal expansion of the piston alloy decreases, its fluidity increases, and the diameter and area fraction of the primary Si in the alloy microstructure increase. The high temperature tensile strength of the alloy is 350 鈩，

本文編號：1786342