本文關(guān)鍵詞： A7N01鋁合金 焊接熱模擬 晶間腐蝕 慢應(yīng)變速率應(yīng)力腐蝕 剝蝕 電化學(xué)測(cè)試　出處：《西南交通大學(xué)》2016年碩士論文　論文類型：學(xué)位論文

【摘要】：A7N01鋁合金屬于7×××系合金中的Al-Zn-Mg合金,目前已被廣泛應(yīng)用于國(guó)內(nèi)外高速列車車體制造領(lǐng)域,而耐蝕性較差已成為制約該合金被大量應(yīng)用的首要因素。高速列車車體大多采用全焊接結(jié)構(gòu),焊接接頭由于受到焊接熱循環(huán)作用,導(dǎo)致其組織發(fā)生明顯變化、力學(xué)性能下降,成為焊接結(jié)構(gòu)最薄弱的區(qū)域。在A7N01鋁合金中,焊接接頭不僅力學(xué)性能降低,合金的耐蝕性也變差,尤其是焊接熱影響區(qū)的耐腐蝕性能最差。而熱影響區(qū)各區(qū)域窄小,難以對(duì)其進(jìn)行分區(qū)研究。因此有必要通過(guò)焊接熱模擬技術(shù)(物理模擬),研究A7N01鋁合金焊接熱影響區(qū)各微區(qū)的組織以及性能。本論文以A7N01鋁合金為研究對(duì)象,采用兩種供貨狀態(tài)的A7N01S-T5型材和A7N01P-T4板材,通過(guò)激光-MIG復(fù)合焊工藝測(cè)試合金的焊接熱循環(huán)曲線,得到焊接熱循環(huán)參數(shù),依照測(cè)試結(jié)果,設(shè)計(jì)四組不同的試驗(yàn)用焊接熱循環(huán)參數(shù),借助Gleeble-3500熱模擬試驗(yàn)機(jī)模擬焊接熱影響區(qū)各微區(qū)組織。對(duì)兩種狀態(tài)合金的母材及熱模擬試件進(jìn)行顯微形貌觀察、第二相分析、拉伸性能、彎曲性能、沖擊韌性、表面硬度等基本力學(xué)性能分析；并對(duì)其在NaCl-H2O2和NaCl-HCl兩種溶液中進(jìn)行晶間腐蝕試驗(yàn),對(duì)其進(jìn)行慢應(yīng)變速率應(yīng)力腐蝕試驗(yàn)、3.5%NaCl溶液中的電化學(xué)測(cè)試、剝蝕試驗(yàn)以及剝蝕溶液中的電化學(xué)測(cè)試。微觀組織分析結(jié)果表明,A7N01S-T5和A7N01P-T4在合金的晶界分布有較多粗大的MgZn2強(qiáng)化相及少量的Al-Fe-Si、Mg2Si等雜質(zhì)相,在晶內(nèi)主要為細(xì)小的MgZn2相。高溫?zé)崮M試件晶界分布有較粗大的MgZn2及呈鏈狀分布的Al-Fe-Si、Mg2Si等雜質(zhì)相；晶內(nèi)主要為細(xì)小的MgZn2相和少量Al-Fe-Si雜質(zhì)相。低溫?zé)崮M試件晶界含較多粗大的MgZn2相和少量Al-Fe-Mn、Mg2Si等雜質(zhì)相,晶內(nèi)有少量細(xì)小的MgZn2相。力學(xué)性能結(jié)果表明,對(duì)A7N01S-T5,高溫?zé)崮M試件強(qiáng)度、延伸率均高于其母材的強(qiáng)度、延伸率,高于低溫?zé)崮M試件的強(qiáng)度、延伸率；高溫?zé)崮M試件沖擊韌性低于母材沖擊韌性,低于低溫?zé)崮M試件的沖擊韌性。對(duì)A7N01P-T4,兩種參數(shù)下熱模擬試件的強(qiáng)度、延伸率均低于其母材的強(qiáng)度、延伸率,但和母材的值相差不大。兩種溶液中(NaCl-H2O2和NaCl-HCl)的晶間腐蝕試驗(yàn)結(jié)果均表明,對(duì)A7N01S-T5,熱模擬試件耐蝕性比母材耐蝕性差,且高溫?zé)崮M試件的耐蝕性最差。對(duì)A7N01P-T4,也是高溫?zé)崮M試件耐蝕性最差,低溫?zé)崮M試件耐蝕性居中,母材耐蝕性最優(yōu)。慢應(yīng)變速率應(yīng)力腐蝕試驗(yàn)結(jié)果表明,對(duì)A7N01S-T5,高溫?zé)崮M試件應(yīng)力腐蝕敏感指數(shù)最高,為0.1262,具有較強(qiáng)的應(yīng)力腐蝕敏感性,斷口形貌主要為二次裂紋,裂紋內(nèi)部為冰糖塊狀的離散晶粒,表現(xiàn)為沿晶型脆性斷裂；低溫?zé)崮M試件及母材應(yīng)力腐蝕敏感性較低。對(duì)A7N01P-T4,也是高溫?zé)崮M試件應(yīng)力腐蝕敏感指數(shù)ISSRT最大,為0.1101,有較強(qiáng)的應(yīng)力腐蝕敏感性,斷口為明顯的脆性斷裂；其低溫?zé)崮M試件和母材的應(yīng)力腐蝕敏感性較低。剝蝕試驗(yàn)結(jié)果表明,在EXCO溶液中腐蝕16h后,A7N01S-T5和A7N01P-T4的熱模擬試件的剝蝕比母材剝蝕嚴(yán)重,且高溫?zé)崮M試件的剝蝕明顯比低溫?zé)崮M試件的剝蝕等級(jí)更高。兩種溶液中(3.5%NaCl和EXCO溶液)的電化學(xué)測(cè)試結(jié)果均表明,對(duì)A7N01S-T5,母材的耐蝕性最優(yōu),其次為低溫?zé)崮M試件,而高溫?zé)崮M試件耐蝕性最差。同樣對(duì)A7N01P-T4,也是高溫?zé)崮M試件耐蝕性最差,腐蝕傾向最大,腐蝕速率最快；低溫?zé)崮M試件次之,母材的腐蝕傾向最低,腐蝕速率最小,極化電阻最大,耐蝕性最優(yōu)。
[Abstract]:A7N01 Aluminum Alloy belongs to Al-Zn-Mg alloy 7 * * * series alloy, has been widely used in domestic and foreign railway vehicle manufacturing field, which has become the bottleneck of the poor corrosion resistance of alloy is the primary factor. A large number of applications in high-speed train mostly adopts full welding structure, welding joint by welding thermal cycle, resulting in the organization changed obviously, the mechanical properties decreased, become the weakest in welding structure. A7N01 Aluminum Alloy, not only the mechanical properties of welded joints decreased, the corrosion resistance of the alloys is poor, especially in the heat affected zone the worst corrosion resistance. The heat affected zone of the regional narrow, difficult zoning on it. It is necessary by using welding thermal simulation technique (physical simulation), A7N01 Aluminum Alloy welding heat affected zone of the micro organization and performance. This paper takes A7N01 as the research object Aluminum Alloy, Using two kinds of state of supply of A7N01S-T5 profiles and A7N01P-T4 plate by laser -MIG hybrid welding process test alloy welding thermal cycle curve of welding thermal cycle parameters, in accordance with the test results, the welding thermal cycle parameters with the design of four different sets of experiments, using Gleeble-3500 thermal simulation testing machine to simulate the welding heat affected zone of the micro structure. The simulation of microscopic observation of specimens of base metal and heat of two alloys, phase analysis, tensile properties, flexural properties, impact toughness, surface hardness analysis of basic mechanical properties; and the intergranular corrosion test in NaCl-H2O2 and NaCl-HCl in two kinds of solution, the slow strain rate stress corrosion test and electrochemical test in 3.5%NaCl solution, the electrochemical erosion test and denudation in solution. The microstructure analysis results showed that A7N01S-T5 and A7N01P-T4 in the amorphous alloy There are many distributed coarse MgZn2 strengthening phase and a small amount of Al-Fe-Si, Mg2Si and other impurities in crystal phase, mainly for the fine MgZn2 phase. Simulation specimens have coarse grain boundary distribution MgZn2 and chainlike distribution of Al-Fe-Si high temperature, Mg2Si and other impurities in the crystal phase; mainly for small MgZn2 or a small amount of Al-Fe-Si impurity phase. Grain boundary simulation specimens containing more coarse MgZn2 phase and a small amount of Al-Fe-Mn low temperature heat, Mg2Si impurity phase, crystal with a small amount of fine MgZn2 particles. The mechanical properties of A7N01S-T5, the simulation results show that the strength of the specimen at high temperature, the elongation elongation is higher than that of the parent material, higher strength, low temperature test pieces the simulation of strength, elongation; simulation specimens impact toughness is lower than that of base metal impact toughness of high temperature heat, low temperature is lower than the thermal simulation test. The impact toughness of A7N01P-T4, two kinds of parameters of thermal simulation specimen strength, elongation rate was lower than the parent material of the strong Degree of elongation, but the base material and the value of the difference. Two kinds of solution (NaCl-H2O2 and NaCl-HCl) of intergranular corrosion test results showed that the A7N01S-T5 thermal simulation specimens corrosion resistance than the base metal poor corrosion resistance, corrosion resistance of the simulation test and the worst heat of A7N01P-T4. Also, is the poor corrosion resistance of simulated specimens of thermal simulation specimens corrosion resistance of middle low temperature heat, corrosion resistance of the base material. The optimal slow strain rate test results show that the A7N01S-T5 simulation specimen stress corrosion sensitivity index was the highest, 0.1262 high temperature, strong stress corrosion sensitivity, fracture the morphology of the major two crack, internal crack as discrete grain sugar loaf, is intergranular brittle fracture; simulation specimens and base material should be low stress corrosion susceptibility of low temperature heat. On A7N01P-T4, simulated specimen stress corrosion sensitivity index ISSRT is maximum heat for 0.1101, There is a strong sensitivity to stress corrosion, the fracture is brittle fracture obviously; the low temperature of specimen and the parent material should be low stress corrosion sensitivity. Erosion test results show that the corrosion in EXCO solution 16h, A7N01S-T5 and A7N01P-T4 thermal simulation specimens of serious erosion than the parent material erosion simulation specimens. The erosion is more obvious than low temperature simulation specimens of higher level and high temperature erosion. Two kinds of solution (3.5%NaCl and EXCO solution) the electrochemical test results show that, for A7N01S-T5, the best corrosion resistance of the base metal, followed by low temperature thermal simulation specimens and high temperature corrosion resistance of simulated specimens is the worst. As of A7N01P-T4, simulation specimens corrosion resistance of the worst is high temperature, corrosion, corrosion rate; low temperature thermal simulation test times, the corrosion tendency of parent material minimum, minimum corrosion rate, polarization resistance, the best corrosion resistance.

【學(xué)位授予單位】：西南交通大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2016
【分類號(hào)】：TG457.14

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