喷射成形超高强度铝合金搅拌摩擦焊接头组织性能研究

发布时间：2018-01-29 08:00

本文关键词： 喷射成形铝合金搅拌摩擦焊显微组织力学性能初始状态　出处：《江苏科技大学》2015年硕士论文　论文类型：学位论文

【摘要】：喷射成形技术制备的铝合金组织均匀细小,无明显宏观偏析,采用传统熔化焊焊接喷射成形铝合金时接头软化现象严重,大大降低材料性能。搅拌摩擦焊作为一种固态焊接方法能有效焊接喷射成形铝合金。对T76态喷射成形7055进行焊接并测温,研究焊接工艺参数对热循环和组织性能的影响。通过拉伸和硬度试验分析工艺参数对接头力学性能的影响,采用OM、SEM等手段对接头进行微观分析,研究工艺参数、组织和性能之间的关系。然后对挤压态、固溶态喷射成形7055进行焊接并对挤压态和固溶态接头进行后续热处理,研究母材初始状态和焊后热处理对接头组织和性能的影响。测温结果表明,搅拌摩擦焊接过程中各点温度先升高再降低。焊缝初始、稳定、结束阶段所达到的温度峰值逐渐上升。各点温度峰值随着旋转速度的提高和焊接速度的降低而上升。后退侧温度低于前进侧温度。距离焊缝上表面越远温度越低。接头宏观上可以看出,飞边主要出现在后退侧,下压量固定的情况下焊接速度减小或旋转速度提高,飞边更加严重。焊核中心区宽度随着焊接速度的减小或旋转速度的提高而变宽。微观分析表明,随着焊接速度的减小和旋转速度的提高,焊核区和部分热机械影响区发生再结晶,力学性能优良,热影响区晶粒长大成为接头薄弱区域。焊核区上部析出相数量少、尺寸大,焊核中下部析出相数量多尺寸较小,焊核中下部出现孔洞。热机械影响区析出相的数量和尺寸与焊核区中下部大体相同但表现出了明显的方向性。热影响区第二相部分溶解,白色颗粒数量少。当旋转速度较小时,析出相数量较少尺寸较小。随着焊接速度的减小,焊核区域析出相出现长大。随着焊接速度和旋转速度的提高,接头抗拉强度和延伸率先降低再提高。转速为1350rpm焊速为75mm/min时,抗拉强度467.12MPa,达到母材强度的86.0%。随着旋转速度的提高,热影响区宽度变大,热影响区最低硬度值变小。不同焊接速度下热影响区宽度变化不大,大约都为3mm,但是热影响区最低硬度值先降低再提高。旋转速度1350rpm,焊速75mm/min时,挤压态、固溶态母材搅拌摩擦焊接均能得到无明显宏观缺陷的接头,并且接头再进行热处理也不出现宏观缺陷。挤压态焊接完后进行T76处理的接头随焊核区晶粒发生异常长大但抗拉强度为496.1MPa,达到母材强度的91.4%,接头显微硬度与母材相当,约195HV。
[Abstract]:The microstructure of aluminum alloy prepared by spray forming technology is uniform and fine, and there is no obvious macro segregation. The softening phenomenon of joint is serious when conventional melting welding is used to weld spray formed aluminum alloy. Friction stir welding (FSW) as a solid-state welding method can effectively weld spray formed aluminum alloy. T76 state spray forming 7055 is welded and temperature measured. The effects of welding parameters on thermal cycling and microstructure and properties were studied. The effects of process parameters on mechanical properties of joints were analyzed by tensile and hardness tests. The relationship among process parameters, microstructure and properties was studied. Then the extrusion, solid solution spray forming 7055 was welded and the extruded and solid solution joints were treated by subsequent heat treatment. The effect of initial state of base metal and heat treatment after welding on the microstructure and properties of joints was studied. The results of temperature measurement showed that the temperature of each point in friction stir welding first increased and then decreased. The temperature peak at the end stage gradually increased. The peak temperature of each point increased with the increase of rotation speed and the decrease of welding speed. The temperature of the receding side was lower than that of the forward side. The farther the temperature was from the upper surface of the weld, the lower the temperature was. The joint can be seen macroscopically. The flange mainly appears in the receding side, and the welding speed decreases or the rotation speed increases when the pressure is fixed. The width of the center zone of the nugget becomes wider with the decrease of the welding speed or the increase of the rotating speed. The microcosmic analysis shows that the width of the center area of the welding nugget increases with the decrease of the welding speed and the increase of the rotation speed. Recrystallization occurs in the nugget zone and part of the thermomechanical zone, and the mechanical properties are good. The grain growth in the HAZ becomes the weak zone of the joint, and the upper part of the nugget zone has a small number of precipitated phases and a large size. The number of precipitated phases in the middle and lower part of the nugget is much smaller. The number and size of precipitated phases in the HAZ are approximately the same as those in the middle and lower parts of the nugget zone but show obvious directionality. The second phase in the HAZ is dissolved. The number of white particles is small. When the rotation speed is small, the number of precipitates is smaller. With the decrease of welding speed, the precipitates in the nugget region grow up, and with the increase of welding speed and rotation speed. The tensile strength and extension of the joint decreased and then increased first. The tensile strength of the joint was 467.12MPa when the welding speed was 75mm / min at 1350rpm. With the increase of rotation speed, the width of HAZ becomes larger, and the minimum hardness value of HAZ becomes smaller. The width of HAZ varies little with different welding speed, all of them are about 3 mm. However, the minimum hardness of the HAZ decreases first and then increases. When the rotation speed is 1350rpm, the welding speed is 75mm / min, the extrusion state is obtained. The joints without macroscopic defects can be obtained by solid solution base metal friction stir welding. The joints treated with T76 after welding in extruded state have abnormal growth but tensile strength is 496.1 MPA. To reach 91.4 of the base metal strength, the microhardness of the joint is about the same as the base metal, about 195HV.
【学位授予单位】：江苏科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG453.9

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