本文關(guān)鍵詞： 鎂合金 鋁合金 Sn-Zn系釬料 異種合金釬焊 動(dòng)力學(xué)　出處：《哈爾濱工業(yè)大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：鎂合金作為最輕、最經(jīng)濟(jì)的金屬結(jié)構(gòu)材料具有比強(qiáng)度和比剛度高、減震吸沖性能強(qiáng)等優(yōu)點(diǎn),被譽(yù)為新世紀(jì)的綠色工程材料,尤其是與鋁合金形成的復(fù)合結(jié)構(gòu),不僅能夠進(jìn)一步減輕構(gòu)件重量,又能同時(shí)發(fā)揮各自的優(yōu)點(diǎn)。但鎂合金和鋁合金在焊接過(guò)程中會(huì)不可避免地產(chǎn)生大量Mg-Al系金屬間化合物,從而嚴(yán)重影響接頭性能。本文采用Sn-Zn系釬料對(duì)AZ31B/3A21接頭進(jìn)行超聲輔助低溫釬焊。針對(duì)異種材料釬焊過(guò)程中出現(xiàn)的界面反應(yīng)不對(duì)稱進(jìn)行分析,結(jié)合數(shù)值模擬計(jì)算和動(dòng)力學(xué)數(shù)學(xué)模型的建立,指導(dǎo)工藝試驗(yàn)并得到最佳工藝參數(shù),分析了釬料成分、工藝參數(shù)(釬焊溫度、保溫時(shí)間)對(duì)釬焊接頭組織及性能的影響機(jī)理。Sn-Zn釬料釬焊AZ31B/3A21異種合金接頭可有效阻隔Mg合金與Al合金反應(yīng)生成有害金屬間化合物,能夠?qū)崿F(xiàn)高質(zhì)量可靠連接。采用Sn-xZn釬料釬焊AZ31B/3A21異種金屬所得的接頭斷裂位置與釬料成分有關(guān)。Sn-3Zn、Sn-9Zn、Sn-30Zn三種釬焊接頭斷裂在AZ31B鎂合金母材與釬料層的反應(yīng)界面Mg2Sn薄層處,其中Sn-30Zn釬焊接頭的平均剪切強(qiáng)度最高,為67.3 MPa;Sn-20Zn接頭斷裂在塊體Mg2Sn富集區(qū)域;在Sn-40Zn接頭中在鎂合金母材附近大量生成的塊狀Mg2Sn連結(jié)成厚層,為易斷裂層;Sn-50Zn接頭斷裂層為釬料與3A21母材反應(yīng)界面,該界面生成Mg-Al系金屬間化合物,平均剪切強(qiáng)度最低,僅20.7MPa。Sn-30Zn釬料為最適合AZ31B/3A21釬焊的最佳成分配比。分析AZ31B/Sn-30Zn/3A21釬縫接頭的微觀組織,在Mg合金與釬料的反應(yīng)界面上存在一層Mg2Sn化合物薄層;釬縫中心區(qū)主要是塊狀Mg2Sn金屬間化合物和固溶體Al-Sn-Zn,且其存在形式為局部彌散分布;在釬料與3A21鋁合金母材側(cè)存在一層Al-Sn-Zn固溶體過(guò)渡層。Al-Sn-Zn固溶體彌散分布于AZ31B/Sn-30Zn/3A21接頭中能夠有效地降低接頭的脆性,釬焊接頭性能顯著改善。針對(duì)AZ31B/Sn-30Zn/3A21接頭的Mg2Sn金屬間化合物薄層,進(jìn)行數(shù)值模擬計(jì)算和元素動(dòng)力學(xué)擴(kuò)散分析。Mg2Sn薄層厚度與接頭剪切強(qiáng)度服從正態(tài)分布規(guī)律,并計(jì)算出Mg2Sn薄層厚度為2μm時(shí)剪切強(qiáng)度最大,可達(dá)69.7MPa;通過(guò)擴(kuò)散分析計(jì)算出任意釬焊溫度和保溫時(shí)間下釬料與鎂合金母材反應(yīng)界面Mg2Sn薄層的理論厚度;在相同的保溫時(shí)間下,釬焊溫度對(duì)Sn原子在Mg中的擴(kuò)散深度影響較大,在相同的釬焊溫度下,保溫時(shí)間對(duì)Sn原子在Mg中的擴(kuò)散深度影響較小,但對(duì)不同深度處Sn原子濃度影響較大。不同的釬焊溫度以及保溫時(shí)間對(duì)接頭的組織性能影響較大。保溫時(shí)間影響焊縫寬度和Mg2Sn存在形態(tài)。釬焊溫度主要決定釬縫中Al-Sn-Zn固溶體的數(shù)量及分布,以及Mg2Sn的形態(tài)和分布。當(dāng)釬焊溫度330℃,保溫時(shí)間5s時(shí),采用Sn-30Zn釬料,在超聲輔助,大氣環(huán)境下無(wú)釬劑釬焊AZ31B/3A21異種金屬接頭的剪切性能最佳,平均為69.2MPa。
[Abstract]:Magnesium alloy, as the lightest and most economical metal structure material, has the advantages of high specific strength and specific stiffness, strong shock absorption and impact absorption, etc. It is praised as the green engineering material in the new century, especially the composite structure formed with aluminum alloy. It can not only further reduce the weight of components, but also play their respective advantages. But magnesium alloy and aluminum alloy will inevitably produce a large number of Mg-Al intermetallics in the welding process. In this paper, ultrasonic assisted low temperature brazing of AZ31B/3A21 joint was carried out with Sn-Zn filler metal. The interface reaction asymmetry occurred in the process of dissimilar material brazing was carried out. Analysis. Combined with the numerical simulation and the establishment of the dynamic mathematical model, the process test was guided and the optimum process parameters were obtained. The composition of the solder and the process parameters (brazing temperature) were analyzed. Heat preservation time). Effect of Sn-Zn brazing filler metal on microstructure and properties of brazed joints AZ31B/3A21 dissimilar alloy joints can be effectively blocked from reaction between mg alloy and Al alloy to form harmful intermetallic compounds. The joint fracture position obtained by Sn-xZn brazing AZ31B/3A21 dissimilar metals is related to the composition of the solder Sn-3ZnN Sn-9Zn. The fracture of Sn-30Zn brazing joints is located at the reaction interface of AZ31B magnesium alloy base metal and filler metal layer, and the average shear strength of Sn-30Zn brazing joint is the highest. 67.3 MPA; The fracture of Sn-20Zn joint is in the enrichment area of block Mg2Sn. A large number of blocks of Mg2Sn formed near the base metal of magnesium alloy in the Sn-40Zn joint are joined into a thick layer, which is easy to fracture. The fracture layer of Sn-50Zn joint is the interface of brazing metal and 3A21 base metal. The intermetallic compound of Mg-Al system is formed at this interface, and the average shear strength is the lowest. Only 20.7 MPa.Sn-30Zn filler metal is the best component ratio for AZ31B/3A21 brazing. Analysis of AZ31B/Sn-30Zn/3A21 brazing joint. Weave. There is a thin layer of Mg2Sn compound on the interface between mg alloy and solder. The central region of brazing joint is mainly block Mg2Sn intermetallic compound and solid solution Al-Sn-Zn.The existence form is local dispersion distribution. A layer of Al-Sn-Zn solid solution transition layer. Al-Sn-Zn solid solution dispersed in AZ31B/Sn-30Zn/3A21 joints on the side of brazing metal and 3A21 aluminum alloy base metal. It can effectively reduce the brittleness of the joint. The properties of brazed joints were improved significantly. The Mg2Sn intermetallic compound thin layers for AZ31B/Sn-30Zn/3A21 joints were obtained. The thickness of mg _ 2SN thin layer and the shear strength of the joint are normally distributed by numerical simulation and elemental dynamic diffusion analysis. The maximum shear strength is obtained when the thickness of Mg2Sn thin layer is 2 渭 m. 69.7 MPA; The theoretical thickness of Mg2Sn thin layer at arbitrary brazing temperature and holding time was calculated by diffusion analysis. At the same holding time, the effect of brazing temperature on the diffusion depth of Sn atom in mg is greater than that on the diffusion depth of Sn atom in mg at the same brazing temperature. Different brazing temperature and holding time have great influence on the microstructure and properties of the joint. The holding time affects the width of weld and the morphology of Mg2Sn, and the main brazing temperature is the soldering temperature. The quantity and distribution of Al-Sn-Zn solid solution in brazing seam should be determined. When the brazing temperature was 330 鈩，

本文編號(hào)：1481135