搅拌摩擦焊接过程中组织演变与力学性能研究

发布时间：2018-07-10 05:22

本文选题：6082-T6铝合金 + 搅拌摩擦焊(FSW)　；参考：《兰州理工大学》2017年硕士论文

【摘要】：随着交通运输业的发展,能源危机的日益加剧,轻量化技术受到越来越多的关注。铝合金因其密度小、比强度高、耐腐蚀、成型性能优良等特点,广泛运用于列车车体。搅拌摩擦焊可以解决铝合金焊接比较困难的问题。试验采用的6082-T6铝合金由于其良好的焊接性、优良的机械加工性能以及较强的耐腐蚀性能,在交通运输和机械工程行业的应用越来越普遍。本文对2mm厚的6082-T6铝合金进行搅拌摩擦焊接,焊后采用透射电子显微镜(TEM)对搅拌摩擦焊缝组织进行研究,采用扫描电镜(SEM)分析焊接接头断口形貌,同时结合组织变化对拉伸强度和硬度变化原因进行分析研究。结果表明:6082-T6铝合金FSW接头焊缝上层与焊缝下层组织发生了变化,各个区域沉淀相分别为:母材主要是β″;焊核区为GP区和尺寸细小的Fe Si2;热影响区为β′。由于受到热输入作用,各个区域都发生了不同程度的动态回复和动态再结晶。显微硬度曲线近似为″W″形,硬度最小值出现在前进侧热影响区。焊缝区接头整体抗拉强度为母材的72%,焊缝区上层的拉伸强度高于焊缝下层。6082-T6铝合金FSW接头匙孔前方中含有β″沉淀相,匙孔后方存在Fe Si2沉淀相。6082-T6铝合金接头纵截面显微硬度在匙孔前后幅值变化较大,匙孔后方硬度显著降低。焊接接头硬度从接头底部到上部,逐渐增大,同时存在的热影响区软化带逐渐扩大。6082-T6铝合金搅拌摩擦焊匙孔前方区域拉伸性能最高,各个区域都含有夹杂相,不同区域的断裂方式都为典型的韧性断裂。针对6082-T6铝合金搅拌摩擦焊接头焊后抗拉强度不高、力学性能较差等原因对搅拌摩擦焊接接头进行自然时效和人工时效处理,结果表明:人工时效处理后显微硬度比焊态和自然时效高10-25HV,人工时效对提高焊核区和热机影响区硬度明显高于自然时效。经过焊后自然时效、人工时效的焊接接头力学性能得到一定程度的提升,人工时效比自然时效抗拉强度提高12%,延伸率降低9%,人工时效提高拉伸强度效果更明显。由于铝合金FSW接头组织成分不均匀,同一焊缝可能会发生多种腐蚀类型,通过对腐蚀后的FSW接头铝合金微观组织形貌进行观察,结合电化学试验发现:6082-T6铝合金搅拌摩擦焊接试样在焊缝中间区域的耐腐蚀性能最好,母材的耐腐蚀性能性能次于匙孔后方和匙孔前方。6082-T6铝合金母材和匙孔前方和匙孔后方发生腐蚀类型主要为晶间腐蚀和剥落腐蚀,随着时间增加,晶间腐蚀和剥落腐蚀程度加剧。焊缝中间区域基本不发生腐蚀。
[Abstract]:With the development of transportation industry and the intensification of energy crisis, the lightweight technology is being paid more and more attention. Aluminum alloy is widely used in train body because of its small density, high strength, corrosion resistance and good molding performance. Friction stir welding can solve the difficult problem of aluminum alloy welding. The 6082-T6 aluminum alloy used in the experiment is used. Because of its good weldability, excellent mechanical processing property and strong corrosion resistance, gold is becoming more and more popular in the transportation and mechanical engineering industry. In this paper, 2mm thick 6082-T6 aluminum alloy was welded by friction stir welding. After welding, transmission electron microscope (TEM) was used to study the structure of friction stir welds, and the scan was scanned. The fracture morphology of welded joints was analyzed by SEM, and the changes of tensile strength and hardness were analyzed with microstructure changes. The results showed that the upper layer of the weld seam of the 6082-T6 aluminum alloy FSW joint and the underlayer of the weld seam changed, and the precipitates in each region were mainly beta, the weld core area was GP and the size of Fe S. I2, the heat affected zone is beta '. Due to the heat input, the dynamic recovery and dynamic recrystallization have occurred in various degrees. The microhardness curve is approximately "W" shape, and the minimum hardness value appears in the forward side heat affected zone. The overall tensile strength of the weld zone joint is 72% of the base material, and the tensile strength of the upper seam zone is higher than that of the weld seam. In the front of the lower.6082-T6 aluminum alloy FSW joint spoon hole, there is a beta precipitation phase in front of the key hole. Behind the keyhole, the microhardness of the longitudinal section of the.6082-T6 aluminum alloy joint with the Fe Si2 precipitation phase changes greatly before and after the keyhole, and the hardness in the rear of the keyhole is significantly reduced. The hardness of the welding joint is gradually increased from the bottom to the upper part of the joint, and the heat affected zone is softened. The tensile property in front of the friction welding spoon hole with gradual expansion of.6082-T6 aluminum alloy is the highest, all regions contain inclusions, and the fracture modes in different regions are typical ductile fracture. The friction welding joints of 6082-T6 aluminum alloy friction stir welding joints are not high after welding, and the mechanical properties are poor. The results of natural aging and artificial aging treatment show that the microhardness of artificial aging is higher than that of welding state and natural aging, and the hardness of artificial aging is obviously higher than that of natural aging. After natural aging after welding, the mechanical properties of the welded joint of artificial aging are improved to a certain extent, and the artificial aging is made by artificial aging. The tensile strength is increased by 12% than that of natural aging, and the elongation is reduced by 9%. The effect of artificial aging on tensile strength is more obvious. Due to the uneven microstructure of the FSW joint of aluminum alloy, many kinds of corrosion types may occur in the same weld seam. The microstructure of the aluminum alloy after corrosion of the FSW joint is observed and the electrochemical test is found to find 6082-T6 The corrosion resistance performance of the aluminum alloy friction stir welding specimens is the best in the middle area of the weld. The corrosion resistance performance of the parent material is second to the rear of the keyhole and the front of the.6082-T6 aluminum alloy and the key hole in front of the keyhole. The corrosion types are mainly intergranular corrosion and peeling corrosion behind the spoon hole, and the intergranular corrosion and the exfoliation corrosion process are increased with time. There is no corrosion in the middle area of the weld.
【学位授予单位】：兰州理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG453.9

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