基于焊缝微观组织形态控制的超声辅助钨极氩弧焊热裂纹抑制方法研究

To solve the bottleneck of serious hot cracking in Gas Tungsten Arc Welding (GTAW) of large dimension copper structures, a new process of ultrasonic assisted GTAW is proposed. Using the cavitation and acoustic streaming effects of ultrasonic, the microstructures and distribution rules of the semi-solid state weld metals in the brittle temperature range (BTR) can be controlled.This process can suppress the hot cracking effectively in welding of large dimension copper structures and obtain fine microstructure of welding joints. Moreover, this process has advantages in improving the performance of the welds and increasing production enficiency without preheating. The emphases of this project are to research the mechanism of weld metal grain refinement under the condition of cavitation and acoustic streaming effects of ultrasonic acting. And influence rules of grain refinement phenomenon on the hot cracking tendency and welds mechanical properties. Establish the rheological model of semisolid weld metal in the BTR when using ultrasonic assisted GTAW process to research the "healing" effects of the liquid phase in the semisolid weld metal, and inherence mechanism of "healing" effects for suppressing the hot cracking. Based on the rigid restraint hot cracking test, a thermal-stress coupled model can be established, which has the abilities of analyzing the hot cracking formation and pre-estimating the hot cracking tendency. Then the ultrasonic assisted GTAW process will be optimized and perfected under the theoretical and experimental study. Overall, the ultrasonic assisted GTAW process is expected to provide a new technical way for the large dimension structure's welding without hot cracking.

为解决紫铜厚大结构件钨极氩弧焊（GTAW）工艺中热裂纹严重的问题，本项目提出超声辅助GTAW新工艺。利用超声波的空化作用和声流作用，对焊接过程中脆性温度区间（BTR）内半固态焊缝金属微观组织形态及分布规律进行控制，有效抑制紫铜厚大结构件焊接热裂纹，获得焊缝金属组织细密均匀的焊接接头，提高焊缝性能。实现厚大结构件不预热焊接，有效降低焊接工艺难度，提高生产效率。着重研究超声辅助GTAW工艺中超声的空化作用及声流作用对焊缝金属晶粒细化的作用机制，研究晶粒细化对热裂倾向及焊缝金属力学性能的影响规律。建立超声辅助GTAW时BTR内半固态焊缝金属的流变模型，研究半固态中液相的填充"愈合"作用对热裂纹的抑制效果及作用机理。基于刚性拘束热裂纹实验，建立具有热裂成因分析能力及热裂倾向预测能力的紫铜厚大件GTAW热力耦合模型，优化并完善超声辅助GTAW工艺，为获得厚大结构件的无热裂纹焊接探索一条新的技术途径。

为解决紫铜厚大结构件钨极氩弧焊（GTAW）工艺中热裂纹严重的问题，本项目提出了超声辅助GTAW新工艺。利用超声波的空化作用和声流作用，对焊接过程中脆性温度区间内（BTR）的半固态焊缝金属微观组织形态及分布规律进行控制，在不增加焊接工艺难度的条件下，有效抑制了紫铜厚大结构件焊接热裂纹，获得焊缝金属组织细密均匀的焊接接头并提高焊缝性能。首先优化了热裂纹形成的判据，基于刚性拘束热裂纹实验建立了具有热裂纹成因分析能力及热裂纹预测能力的紫铜厚大结构件钨极氩弧焊热力耦合模型。其次，设计并研发了超声辅助设备，实现了弧焊与超声辅助实时同步进行。再次，建立了超声作用下紫铜板振动规律有限元模型，分析了声波在试板中的传递规律。最后，研究了超声辅助GTAW工艺条件下超声施加方式及功率对紫铜板堆焊、对焊等形式接头的作用效果及规律，着重研究了超声的空化作用及声流作用对焊缝金属晶粒细化的作用机制，研究晶粒细化对热裂倾向及焊缝金属力学性能的影响规律。