本文關鍵詞： 兩相區(qū)連鑄 銅錫合金 晶包晶組織 化學成分 力學性能　出處：《北京科技大學》2017年博士論文　論文類型：學位論文

【摘要】：Cu-Sn合金具有較高的強度、良好的抗磨性和抗腐蝕性等優(yōu)點,在工業(yè)領域有廣闊的應用前景。但是,由于Cu-Sn合金具有較寬的固液兩相區(qū),采用傳統(tǒng)方法制備的合金存在嚴重的偏析行為,合金的成分分布很不均勻。同時,合金的塑性以及導電性能較差,嚴重影響了合金的使用性能。兩相區(qū)連鑄技術適合制備具有寬固液兩相區(qū)的合金,現(xiàn)行研究結(jié)果表明,采用兩相區(qū)連鑄技術可制備具有柱狀晶組織的合金,合金的綜合性能顯著提高。本論文系統(tǒng)研究了兩相區(qū)連鑄Cu-4.7 wt%Sn合金的成分分布規(guī)律,探討了兩相區(qū)連鑄Cu-4.7 wt%Sn合金反偏析的形成機理。其次,深入分析了兩相區(qū)連鑄Cu-4.7wt%Sn合金的力學性能、導電性能與微觀組織之間的關系,對微觀組織進行了三維透視成像表征以及量化表征,并在量化表征的基礎上,建立了兩相區(qū)連鑄Cu-4.7 wt%Sn合金微觀組織與工藝參數(shù)之間的定量關系模型。最后,對兩相區(qū)連鑄Cu-4.7wt%Sn合金的微觀組織形成機理進行了研究。所得結(jié)果可為發(fā)展兩相區(qū)連鑄技術及其在工業(yè)中的應用奠定理論基礎,研究工作取得了以下主要結(jié)果。采用兩相區(qū)連鑄技術制備得到的Cu-4.7wt%Sn合金成分分布均勻,內(nèi)部組織致密,無明顯缺陷。鑄型內(nèi)固液界面形貌對Cu-4.7wt%Sn合金成分分布有重要影響,若合金在鑄型內(nèi)的固液界面平直,可制備出表面質(zhì)量良好,成分分布均勻的Cu-4.7wt%Sn合金;若合金的中央部分率先開始凝固,形成合金中部略微向上凸起的固液界面,而合金的兩側(cè)呈現(xiàn)出順"八"字的斜面狀固液界面,導致斜面狀固液界面與型壁之間形成狹小的縫隙,則會形成反偏析現(xiàn)象。主要原因是縫隙內(nèi)的液相金屬富集大量Sn溶質(zhì),富含Sn溶質(zhì)的液相合金具有較低的熔點,在鑄型的高溫區(qū)不能凝固而附著在已凝固合金的表面,在鑄型低溫區(qū)完成凝固成為合金的表面層,導致了兩相區(qū)連鑄Cu-4.7 wt%Sn合金反偏析的形成。兩相區(qū)連鑄Cu-4.7 wt%Sn合金的平均抗拉強度為267 MPa,斷后伸長率最高達到49%,與普通冷型連鑄Cu-4.7wt%Sn合金相比,合金的抗拉強度與斷后伸長率明顯提高。由于兩相區(qū)連鑄Cu-4.7 wt%Sn合金的微觀組織主要由柱狀晶,柱狀晶晶界之間的小晶粒以及晶包晶(一個柱狀晶完全包覆至少一個小晶粒的組織)組成,因而合金在形變時,柱狀晶之間的協(xié)調(diào)變形能有效提高合金的斷后伸長率。同時,由于許多柱狀晶內(nèi)都含有不少具有自封閉晶界的小晶粒,當小晶粒的晶界由于移動困難而產(chǎn)生裂紋時,不存在裂紋沿晶界進行擴展的行為。在拉伸形變過程中產(chǎn)生的位錯會大量塞積在小晶粒的晶界處,在柱狀晶內(nèi)形成"位錯島"。正是由于兩相區(qū)連鑄Cu-4.7%Sn合金拉伸變形過程中這些"位錯島"的出現(xiàn),對位錯的滑移起到了很強的釘扎作用,從而使得抗拉強度明顯增加。兩相區(qū)連鑄Cu-4.7 wt%Sn合金的電阻率為8.937×10-6 Ω·cm,與普通冷型連鑄Cu-4.7wt%Sn合金相比,電導率提升了 12.2%。其主要原因是兩相區(qū)連鑄Cu-4.7%Sn合金中的橫向晶界較少,其次,柱狀晶內(nèi)的小晶粒只占很少的面積,有助于減少電子的散射。結(jié)合二維金相與計算機三維圖像處理技術可獲得晶包晶組織的透視成像表征,在三維透視成像的基礎上,綜合考慮小晶粒的大小、被包覆小晶粒的數(shù)量、柱狀晶晶界處小晶粒的數(shù)量、合金外表面小晶粒數(shù)量、柱狀晶的數(shù)量、柱狀晶的大小、包覆小晶粒的柱狀晶數(shù)量、單個柱狀晶包覆小晶粒的最大數(shù)量和最小數(shù)量等可以實現(xiàn)具有晶包晶微觀組織的量化表征。利用BP人工神經(jīng)網(wǎng)絡建立了兩相區(qū)連鑄制備工藝與具有晶包晶微觀組織之間的定量關系模型,所構(gòu)建的BP人工神經(jīng)網(wǎng)絡模型具有較高的精度。實驗與有限元數(shù)值模擬結(jié)果表明,在鑄型的出口處,合金被強制冷卻,鑄型內(nèi)熱流的方向近似平行于[001]方向,晶粒沿熱流方向相反的方向進行生長形成柱狀晶粒。在鑄型的型壁以及固液界面前沿存在小晶粒的形核和長大,小晶粒生長的方向較為隨機,當小晶粒的[001]方向與熱流方向平行時,小晶�？赡芾^續(xù)向上生長,形成新的柱狀晶粒。當小晶粒的[001]方向與熱流方向非平行時,小晶粒在各個方向均不存在快速的生長方向,生長緩慢,被快速向上生長的柱狀晶粒包覆,形成柱狀晶粒包覆小晶粒的晶包晶組織。
[Abstract]:Cu-Sn alloy has high strength, abrasion resistance and corrosion resistance and other advantages of good, has a broad application prospect in the industrial field. However, due to the Cu-Sn alloy with the solid-liquid two-phase region wide, there exists serious segregation behavior of alloy prepared by traditional method, the alloy components are very unevenly distributed. At the same time. Alloy plastic and conductive performance is poor, a serious impact on the performance of the alloy. The alloy casting technology is suitable for the preparation of the two-phase region wide solid-liquid two-phase region, the results show that the two-phase region can be prepared by casting alloy with columnar grain structure, the mechanical properties of the alloys increased significantly. The distribution of components this dissertation has systematically studied the two-phase region casting Cu-4.7 wt%Sn alloy, discusses the two-phase region casting Cu-4.7 wt%Sn alloy anti segregation mechanism. Secondly, in-depth analysis of the two-phase region casting Cu-4.7wt%Sn alloy force School performance, the relationship between conductivity and microstructure, the microstructure of the 3D X-ray imaging characterization and quantitative characterization, and on the basis of quantitative characterization on the establishment of a quantitative model of relationship between microstructure and process parameters of two-phase region casting Cu-4.7 wt%Sn alloy were studied. Finally, the mechanism of microstructure formation in the two-phase region continuous casting of Cu-4.7wt%Sn alloy. The results for the development of two-phase continuous casting technology and its application in industry and lay the theoretical foundation, research results are as follows. The composition of Cu-4.7wt%Sn alloy prepared by continuous casting technology for two-phase region distribution, dense internal organization, without obvious defects. The solid-liquid interface morphology has an important effect on the mold the distribution of Cu-4.7wt%Sn alloy components, if the alloy in the mould of the solid-liquid interface is flat, can be prepared with good surface quality and uniform distribution of Cu components -4.7wt%Sn鍚堥噾;鑻ュ悎閲戠殑涓ぎ閮ㄥ垎鐜囧厛寮，

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