摘要本文以AZ31镁合金为研究对象，基于镁合金板和铜箔叠层试验对超声协同搅拌摩擦焊焊接接头中的塑性流动进行观察与研究，并结合金相试验和硬度试验进一步探究超声振动对搅拌摩擦焊的组织和性能的影响。86748

超声系统搅拌摩擦焊塑性流场试验结果表明：在焊缝横截面上，搅拌区的金属流动被分为3个区域。在前进侧的金属一部分从向下往上流动，另一部分随搅拌头的轴肩的下压力向下流动；后退侧的金属一部分堆积挤压进入后退侧，另一部分金属随搅拌头的轴肩平行流动到后退侧。在焊缝纵截面上，焊缝被分为受轴肩影响的表面流动区，流动轨迹发生变化的中间过渡区，受搅拌针影响的竖直流动区以及受搅拌针端部影响的挤压流动区。各个区域由于金属受到的作用条件不同，发生不同的金属流动。

硬度试验表明：加入超声振动后的焊接接头搅拌区的硬度明显提高，说明超声振动的施加不仅可以强化塑性流场，在塑性流动更加充分的前提下，接头性能也得到提升。

金相试验表明：加入超声振动后焊后金属的晶粒度等级明显提高，说明超声振动可以有效的细化晶粒，使得焊核区的晶粒更为细化，并且分布也更加均匀。

毕业论文关键词：超声振动；搅拌摩擦焊；塑性流场；叠层试验

Abstract This paper uses the AZ31 magnesium alloy as the research object, based on the stacking layer test of magnesium alloy plate and copper foil, working on the observation and research on the ultrasonic friction stir welding joint。 Then the research further explore the effect of ultrasonic vibration on the microstructure and mechanical properties of friction stir welding, combined with metallographic test and micro-hardness test。

Plastic flow of ultrasonic friction stir welding test shows that in the cross-section of the weld, the metal flow mixing zone is pided into 3 regions。 Part of the metal which is on the advancing side of the joint moves upwards, another part flows downwards with the threads of stirring tool because of the pressure of the shoulder。 Part of the metal which is on the retreating side is pressed into the retreating side, and the other part of the metal flows to the advancing side with the shoulder。 In the longitudinal section of the weld, the weld is pided into the surface-flow-area which is influenced by the shoulder, the transitional zone where flow track changes, vertical flow zone which is affected by the pin and the extrusion flow region which is affected by the end of the pin。 Each region has different metal flow because of the different working conditions of the metal。

The hardness test shows that the hardness of the welded joint after adding ultrasonic vibration is increasing obviously, meaning that the application of ultrasonic vibration can not only strengthens the plastic flow field, but also improves the performance of the joints under the condition that the plastic flow is adequate。

Metallographic test shows that the grain size of the metal increases obviously after the addition of ultrasonic vibration, which shows that ultrasonic vibration can refine the grains effectively, making the grain in the nugget zone more refined, and makes the distribution more uniform。

Key words：Friction stir welding; plastic flow field; ultrasonic vibration; stacking test

目  录

第一章 绪  论 1

1。1 引言 1

1。2 镁合金 1

1。2。1 镁合金的性能 1

1。2。2 镁合金的应用 2

1。3 搅拌摩擦焊 2

1。3。1 搅拌摩擦焊的原理