本文選題：7XXX鋁合金　切入點(diǎn)：攪拌摩擦焊　出處：《北京交通大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：某7XXX鋁合金具有比強(qiáng)度高、力學(xué)性能好等特點(diǎn),是高速列車側(cè)墻、枕梁等結(jié)構(gòu)件常用材料。目前國(guó)內(nèi)外關(guān)于該7XXX鋁合金組織性能的研究較少,然而接頭組織性能的研究可以為工藝參數(shù)的選擇提供理論支持,從而提高企業(yè)焊接產(chǎn)品質(zhì)量。本文將對(duì)15mm厚度的某7XXX鋁合金攪拌摩擦焊焊縫成形機(jī)理、焊接接頭組織形貌及第二相特征進(jìn)行研究,并分析組織對(duì)焊接接頭力學(xué)性能的影響。本文研究?jī)?nèi)容及成果如下:(1)從焊接熱輸入和材料流動(dòng)行為兩方面對(duì)焊縫的成形機(jī)理進(jìn)行了研究,并探討了焊接工藝參數(shù)對(duì)焊縫成形質(zhì)量的影響。(2)通過(guò)目視檢驗(yàn)和X射線檢測(cè)法比選出了無(wú)焊接缺陷的工藝參數(shù)。焊接速度為200 mm/min,轉(zhuǎn)速為 300 rpm、400 rpm;焊接速度為 300 mm/min,轉(zhuǎn)速為 400 rpm,兩組參數(shù)下均能得到無(wú)缺陷焊接接頭。(3)利用光學(xué)顯微鏡,分析了無(wú)焊接缺陷的焊接接頭不同區(qū)域組織形貌特點(diǎn)。沿水平方向,焊接接頭各區(qū)域組織形貌差別較大,焊核區(qū)為細(xì)小等軸晶,熱機(jī)影響區(qū)組織發(fā)生明顯的彎曲變形,熱影響區(qū)為粗化的板條組織。(4)利用掃描電鏡和能譜儀,分析了無(wú)焊接缺陷的焊接接頭不同區(qū)域第二相特征。母材第二相包括大量不溶雜質(zhì)相AlMnSiFe、固溶體Al6(FeMn)和少量強(qiáng)化相T(Al2Mg3Zn3)、η(MgZn2),焊核區(qū)強(qiáng)化相發(fā)生析出。(5)基于顯微硬度計(jì)測(cè)試結(jié)果,分析了焊接接頭的顯微硬度特征。焊核區(qū)硬度與母材區(qū)硬度值大致相當(dāng),平均值約121HV;熱影響區(qū)硬度值125HV～140HV左右。以焊縫中心為界,AS側(cè)熱機(jī)影響區(qū)硬度值有突變現(xiàn)象;RS側(cè)硬度值從焊核區(qū)到熱影響區(qū)方向逐漸升高。(6)基于萬(wàn)能拉伸試驗(yàn)機(jī)、斷口形貌分析、殘余應(yīng)力等測(cè)試結(jié)果,分析了焊接接頭的拉伸性能。焊接接頭平均拉伸強(qiáng)度為403MPa,斷后伸長(zhǎng)率為16.3%。焊接接頭斷裂位置位于AS側(cè)熱影響區(qū),沿45°方向切斷,斷口呈纖維狀,屬于韌性斷裂。本文主要研究了某7XXX鋁合金攪拌摩擦焊焊接接頭組織和力學(xué)性能。通過(guò)理論與試驗(yàn)相結(jié)合的方法,分析了接頭工藝參數(shù)對(duì)焊縫成形的影響;焊接接頭組織形貌特點(diǎn)和第二相特征;組織對(duì)力學(xué)性能的影響。研究成果對(duì)指導(dǎo)企業(yè)選擇出合理的焊接工藝參數(shù),提高攪拌摩擦焊焊縫質(zhì)量具有重要意義。
[Abstract]:A certain 7XXX aluminum alloy has the characteristics of high specific strength, good mechanical properties and so on. It is a common material for the side wall and pillow beam of high-speed train. At present, there are few researches on the microstructure and properties of the 7XXX aluminum alloy at home and abroad. However, the study of the microstructure and properties of the joints can provide theoretical support for the selection of process parameters and improve the quality of welding products in the enterprise. In this paper, the mechanism of weld formation of a 7XXX aluminum alloy with 15mm thickness friction stir welding is studied. The microstructure and phase characteristics of welded joints were studied. The effect of microstructure on the mechanical properties of welded joints is analyzed. The research contents and results are as follows: 1) the mechanism of weld forming is studied from the aspects of welding heat input and material flow behavior. The influence of welding process parameters on the quality of weld formation was also discussed. (2) the parameters without welding defects were selected by visual inspection and X-ray inspection. The welding speed was 200 mm / min, the rotational speed was 300 rpm, and the welding speed was 300 rpm; the welding speed was 300 mm / min; the welding speed was 300 mm / min; the welding speed was 300 mm / min; the welding speed was 300 mm / min. Mm / min, at a speed of 400 rpm, and both sets of parameters can be used to obtain a defect free welded joint. The characteristics of microstructure in different regions of welded joints without welding defects are analyzed. Along the horizontal direction, the microstructure of welded joints varies greatly, the nugget zone is small equiaxed crystal, and the microstructure of the zone affected by heat engine has obvious bending deformation. The heat affected zone (HAZ) is a roughened lath structure, which is characterized by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The second phase characteristics in different regions of welded joints without welding defects are analyzed. The second phase of the base metal consists of a large amount of insoluble impurity phase AlMnSiFeFe (solid solution Al6FeMn) and a small amount of strengthening phases TnAl2Mg3Zn3Zn3ZN, 畏 _ (2) MgZn2ZN _ (2), and the strengthened phases in the nugget zone are precipitated. 5) based on the results of microhardness measurement, The microhardness characteristics of welded joints are analyzed. The hardness of the nugget zone is approximately the same as the hardness value of the base metal area. The average value is about 121 HVV, and the hardness value of heat affected zone is about 125 HVN 140 HV. The hardness of RS side increases gradually from the direction of nuke zone to heat affected zone, and the hardness value of RS side increases gradually from the direction of nuke zone to heat affected zone.) based on the universal tensile testing machine, the fracture morphology is analyzed. The tensile properties of the welded joints were analyzed by the residual stress test results. The average tensile strength of the welded joints was 403MPa, and the elongation after breaking was 16.3.The fracture position of the welded joints was located in the heat affected zone of as side, which was cut in the direction of 45 擄, and the fracture was fibrous. This paper mainly studies the microstructure and mechanical properties of a 7XXX aluminum alloy friction stir welding joint. By combining theory with experiment, the influence of welding process parameters on weld forming is analyzed. The microstructure and second phase characteristics of welded joints, the effect of microstructure on mechanical properties, and the research results are of great significance to guide enterprises to select reasonable welding process parameters and improve welding quality of friction stir welding.
【學(xué)位授予單位】：北京交通大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：TG407

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