本文選題：A356鋁合金輪轂 + 低壓加局部擠壓鑄造��； 參考：《華南理工大學(xué)》2015年碩士論文

【摘要】：由于低壓鑄造成形壓力較小,凝固過程中輪轂鑄件厚壁部位易產(chǎn)生縮孔／縮松缺陷,導(dǎo)致輪轂力學(xué)性能和服役使用性能降低。局部擠壓法作為一種專門技術(shù),可通過對鑄件厚壁部位施加壓力而改善其內(nèi)部孔洞缺陷,近年來在壓鑄工藝上得到廣泛應(yīng)用。本文提出了低壓加局部擠壓鑄造的輪轂成形方法,重點(diǎn)研究了該成形中“鑄造工藝—微觀組織—力學(xué)性能”三者之間的聯(lián)系。首先設(shè)計(jì)了輪轂低壓加局部擠壓鑄造總體方案,利用AnyCasting軟件對輪轂低壓鑄造充型和凝固過程進(jìn)行模擬,研究了鑄件關(guān)鍵部位凝固溫度場的變化規(guī)律。結(jié)果表明,鑄件中輪輞部位冷卻速度最快,輻條部位次之,輪芯部位最慢。基于模擬結(jié)果,確定了局部擠壓工藝參數(shù)范圍,其中擠壓延遲時(shí)間范圍為67.63～103.15 s；擠壓速度分為兩個(gè)階段,低速階段(0.1 mm/sV10.2 mm/s)和高速階段(0.4 mm/sV20.7 mm/s);擠壓桿的最大位移為71mm。采用低壓加局部擠壓鑄造工藝制備了A356鋁合金輪轂,分析了不同工藝條件下鑄件關(guān)鍵部位的微觀組織,并基于X射線三維斷層掃描技術(shù)研究了工藝條件對輻條部位內(nèi)部孔洞三維形貌與特征的影響。結(jié)果表明,局部擠壓工藝對輪轂鑄件的作用主要體現(xiàn)在輪芯和輻條部位。對于輪芯部位,由于受到擠壓力和冷卻速度的共同作用,心部尚未凝固的金屬液發(fā)生非平衡凝固,組織中含有大量的α-Al初生相。對于輻條部位,凝固前期受擠壓力作用明顯,得到來自輪芯的富Si液相的強(qiáng)制流動(dòng)補(bǔ)縮,輻條處Si粒子體積分?jǐn)?shù)較高；隨著凝固的進(jìn)行,凝殼變形抗力和枝晶阻礙力不斷增大,補(bǔ)縮作用下降,導(dǎo)致輻條部位仍存在少量孔洞缺陷。研究了低壓加局部擠壓A356鋁合金輪轂的拉伸和沖擊性能,探討了鑄件微觀組織與力學(xué)性能之間的關(guān)系。結(jié)果表明,與低壓鑄造工藝相比,經(jīng)局部擠壓后輪轂鑄件的拉伸性能得到了提高。其中當(dāng)擠壓速度V2為0.5 mm/s,擠壓時(shí)間T2為50s時(shí),輪轂鑄件的綜合拉伸性能最優(yōu)。輪轂鑄件的抗拉強(qiáng)度和伸長率主要受孔洞和氧化膜等缺陷以及二次枝晶間距的影響；而屈服強(qiáng)度主要受Mg2Si析出相的影響�；貧w分析表明,鋁合金輪轂鑄件的沖擊韌性主要受孔洞和氧化膜缺陷影響,總體上試樣沖擊韌性隨著斷面缺陷總面積的增加而降低。
[Abstract]:Due to low pressure casting forming pressure, shrinkage hole / shrinkage defect is easy to occur in the thick wall of hub casting during solidification, which results in the decrease of mechanical properties and service performance of hub. As a special technique, local extrusion can improve the internal cavity defects by applying pressure on the thick wall of castings. It has been widely used in die casting technology in recent years. In this paper, the forming method of wheel hub with low pressure and local squeeze casting is put forward, and the relationship between "casting process, microstructure and mechanical properties" in the forming process is mainly studied. Firstly, the overall scheme of hub low pressure and local squeeze casting is designed, and the mold filling and solidification process of hub low pressure casting are simulated by AnyCasting software, and the variation law of solidification temperature field in key parts of the casting is studied. The results show that the cooling speed of the rim is the fastest, the spoke is the second, and the core is the slowest. Based on the simulation results, the range of local extrusion parameters is determined, in which the extrusion delay time range is 67.63 ~ 103.15 s, the extrusion speed is divided into two stages, the low speed stage is 0. 1 mm/sV10.2 / mm / s) and the high speed stage is 0. 4 mm/sV20.7 / mm / s, and the maximum displacement of the extruding rod is 71 mm. The A356 aluminum alloy wheel hub was prepared by low pressure and local squeeze casting. The microstructure of the key parts of the casting under different technological conditions was analyzed. The effect of the process conditions on the three-dimensional morphology and characteristics of the voids in the spokes was studied based on the X-ray 3D scanning technique. The results show that the effect of local extrusion on hub casting is mainly reflected in wheel core and spoke position. For the core, due to the joint action of extrusion pressure and cooling rate, non-equilibrium solidification occurs in the liquid metal which has not yet solidified in the center, and there are a large number of 偽 -Al primary phases in the microstructure. For the spokes, the extrusion force is obvious in the early stage of solidification, the forced flow of Si-rich liquid phase from the wheel core is obtained, the volume fraction of Si particles at the spokes is higher, and with the solidification, the deformation resistance and dendrite resistance of solidification increase continuously. The decrease of shrinkage results in a small number of holes in the spokes. The tensile and impact properties of A356 aluminum alloy wheel with low pressure and local extrusion were studied, and the relationship between microstructure and mechanical properties of the casting was discussed. The results show that the tensile properties of the hub castings after local extrusion are improved compared with the low pressure casting process. When the extrusion speed V2 is 0.5 mm / s and the extrusion time T2 is 50 s, the overall tensile properties of the hub castings are optimal. The tensile strength and elongation of hub castings are mainly affected by defects such as holes and oxide films and secondary dendrite spacing while the yield strength is mainly affected by Mg2Si precipitates. Regression analysis shows that the impact toughness of aluminum alloy wheel castings is mainly affected by holes and oxide film defects, and the impact toughness decreases with the increase of the total area of section defects.
【學(xué)位授予單位】：華南理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：TG249.2;TG146.21

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本文編號(hào)：1980588