A7N01铝合金焊接热模拟及微区腐蚀性能研究

发布时间：2018-01-19 10:18

本文关键词： A7N01铝合金焊接热模拟晶间腐蚀慢应变速率应力腐蚀剥蚀电化学测试　出处：《西南交通大学》2016年硕士论文　论文类型：学位论文

【摘要】：A7N01铝合金属于7×××系合金中的Al-Zn-Mg合金,目前已被广泛应用于国内外高速列车车体制造领域,而耐蚀性较差已成为制约该合金被大量应用的首要因素。高速列车车体大多采用全焊接结构,焊接接头由于受到焊接热循环作用,导致其组织发生明显变化、力学性能下降,成为焊接结构最薄弱的区域。在A7N01铝合金中,焊接接头不仅力学性能降低,合金的耐蚀性也变差,尤其是焊接热影响区的耐腐蚀性能最差。而热影响区各区域窄小,难以对其进行分区研究。因此有必要通过焊接热模拟技术(物理模拟),研究A7N01铝合金焊接热影响区各微区的组织以及性能。本论文以A7N01铝合金为研究对象,采用两种供货状态的A7N01S-T5型材和A7N01P-T4板材,通过激光-MIG复合焊工艺测试合金的焊接热循环曲线,得到焊接热循环参数,依照测试结果,设计四组不同的试验用焊接热循环参数,借助Gleeble-3500热模拟试验机模拟焊接热影响区各微区组织。对两种状态合金的母材及热模拟试件进行显微形貌观察、第二相分析、拉伸性能、弯曲性能、冲击韧性、表面硬度等基本力学性能分析；并对其在NaCl-H2O2和NaCl-HCl两种溶液中进行晶间腐蚀试验,对其进行慢应变速率应力腐蚀试验、3.5%NaCl溶液中的电化学测试、剥蚀试验以及剥蚀溶液中的电化学测试。微观组织分析结果表明,A7N01S-T5和A7N01P-T4在合金的晶界分布有较多粗大的MgZn2强化相及少量的Al-Fe-Si、Mg2Si等杂质相,在晶内主要为细小的MgZn2相。高温热模拟试件晶界分布有较粗大的MgZn2及呈链状分布的Al-Fe-Si、Mg2Si等杂质相；晶内主要为细小的MgZn2相和少量Al-Fe-Si杂质相。低温热模拟试件晶界含较多粗大的MgZn2相和少量Al-Fe-Mn、Mg2Si等杂质相,晶内有少量细小的MgZn2相。力学性能结果表明,对A7N01S-T5,高温热模拟试件强度、延伸率均高于其母材的强度、延伸率,高于低温热模拟试件的强度、延伸率；高温热模拟试件冲击韧性低于母材冲击韧性,低于低温热模拟试件的冲击韧性。对A7N01P-T4,两种参数下热模拟试件的强度、延伸率均低于其母材的强度、延伸率,但和母材的值相差不大。两种溶液中(NaCl-H2O2和NaCl-HCl)的晶间腐蚀试验结果均表明,对A7N01S-T5,热模拟试件耐蚀性比母材耐蚀性差,且高温热模拟试件的耐蚀性最差。对A7N01P-T4,也是高温热模拟试件耐蚀性最差,低温热模拟试件耐蚀性居中,母材耐蚀性最优。慢应变速率应力腐蚀试验结果表明,对A7N01S-T5,高温热模拟试件应力腐蚀敏感指数最高,为0.1262,具有较强的应力腐蚀敏感性,断口形貌主要为二次裂纹,裂纹内部为冰糖块状的离散晶粒,表现为沿晶型脆性断裂；低温热模拟试件及母材应力腐蚀敏感性较低。对A7N01P-T4,也是高温热模拟试件应力腐蚀敏感指数ISSRT最大,为0.1101,有较强的应力腐蚀敏感性,断口为明显的脆性断裂；其低温热模拟试件和母材的应力腐蚀敏感性较低。剥蚀试验结果表明,在EXCO溶液中腐蚀16h后,A7N01S-T5和A7N01P-T4的热模拟试件的剥蚀比母材剥蚀严重,且高温热模拟试件的剥蚀明显比低温热模拟试件的剥蚀等级更高。两种溶液中(3.5%NaCl和EXCO溶液)的电化学测试结果均表明,对A7N01S-T5,母材的耐蚀性最优,其次为低温热模拟试件,而高温热模拟试件耐蚀性最差。同样对A7N01P-T4,也是高温热模拟试件耐蚀性最差,腐蚀倾向最大,腐蚀速率最快；低温热模拟试件次之,母材的腐蚀倾向最低,腐蚀速率最小,极化电阻最大,耐蚀性最优。
[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.

【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG457.14

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