AZ31镁合金搅拌摩擦焊接头显微组织及腐蚀性能研究

发布时间：2018-07-23 10:25

【摘要】：镁合金的焊接、腐蚀及防护问题与其应用密切相关,随着焊接技术的快速发展,已实现了镁合金构件的高性能连接。而针对镁合金焊接接头的腐蚀行为、防护机制及其与接头显微结构相关性的研究开展较少。因此,系统开展镁合金搅拌摩擦焊(FSW)接头的腐蚀行为与防护技术的研究,揭示接头的腐蚀机制、为接头的防护以及提高其服役寿命,具有重要的理论意义和实际价值。本文以AZ31镁合金搅拌摩擦焊接头为研究对象,分析了搅拌摩擦焊接参数对接头显微组织及力学性能的影响,针对镁合金耐蚀性差的特点,系统的研究了接头在NaCl溶液中的腐蚀行为,并采用冷喷涂纯铝的方法对其进行防护,获得以下主要结论。FSW焊接工艺的改变,会引起焊接热输入量的变化,热输入量过大或过小都会造成接头成形差、力学性能低;在焊接速度120mm/min,搅拌头转速转速1200r/min时,焊缝成形良好,抗拉强度最高,达221.7MP,约为母材强度的83%。在不同的热处理温度及保温时间下,焊接接头各区域组织会产生不同的变化,组织形态的改变会引起硬度产生相应的变化。在热处理温度T=250℃保温时间t=2h时,焊接接头各区域组织趋于均匀化,平均显微硬度不低于78Hv达到最高。AZ31镁合金FSW焊缝的腐蚀电位和母材相近,而母材的腐蚀电流密度为0.00045A/cm2,焊缝为0.00163A/cm2,相差近一个数量级。由于焊接接头的焊缝区受到晶粒尺寸及β相析出的影响,导致焊缝耐蚀性能最差,腐蚀最先从该区域产生。针对AZ31镁合金FSW焊缝的耐蚀性不如母材的耐蚀性好的缺点,通过冷喷涂工艺优化,在给粉机转速R=0.4r/min进给速度S=600mm/min时,获得了与机体结合紧密、孔隙率低的涂层。纯铝涂层自腐蚀电位高、腐蚀电流降低,所能明显改善焊接接头的耐腐蚀性能。由此可见,本文通过研究焊接接头的腐蚀机制,掌握焊接接头关键部位的腐蚀规律,采用了合理的防护措施,实现了对AZ31镁合金搅拌摩擦焊接接头的长效防护。
[Abstract]:The welding, corrosion and protection of magnesium alloy are closely related to its application. With the rapid development of welding technology, the high performance connection of magnesium alloy components has been realized. However, few researches have been carried out on the corrosion behavior of magnesium alloy welded joints, the protective mechanism and their correlation with the microstructure of the joints. Therefore, it is of great theoretical significance and practical value to systematically study the corrosion behavior and protection technology of magnesium alloy friction stir welding (FSW) joints, to reveal the corrosion mechanism of the joints, to protect the joints and to improve their service life. In this paper, the effect of friction stir welding parameters on microstructure and mechanical properties of AZ31 magnesium alloy friction stir welding joint is analyzed. The corrosion behavior of joints in NaCl solution was systematically studied, and the cold sprayed pure aluminum was used to protect the joints. The following main conclusions were obtained: the change of welding process of FSW would cause the change of welding heat input. When the welding speed is 120mm / min and the speed of stirring head is 1200r/min, the weld is formed well and the tensile strength is the highest (221.7 MPP), which is about 833% of the base metal strength. Under different heat treatment temperature and holding time, the microstructure of welded joint will change in different regions, and the change of microstructure will lead to the corresponding change of hardness. When the heat treatment temperature is 250 鈩，

本文编号：2139097