Identification of the influence of mechanical vibrations on the solidification process during deep penetration welding

机械振动对液态金属凝固过程中的晶粒长大有显著影响。这种效应被用作一种机械精炼方法，并在铸造工艺中得到了很好的证实。将该方法应用于0~5 kHz频率范围内的激光深熔焊接，对熔合区的晶粒组织也产生了有利的影响。然而，在相对较快的激光深熔焊接中，这种细化效果背后的主要影响因素和机理还没有完全被了解。在本研究项目范围内，这一机制和影响因素应通过实验调查的方式确定。主要假设是，在较高的频率下，细化效果更有效，并且主要是基于熔池和凝固前沿之间额外的相对运动而导致的晶粒剥离。了解影响这一效应的主要因素，可以为今后开发能够产生细晶组织的高效系统技术提供依据，从而改善焊缝性能，特别是减少热裂纹的发生。

Mechanical vibrations can significantly influence the grain growth during solidification of liquid metals. This effect is used as a mechanical refinement method and is well established in casting technology. Using this method in deep penetration laser beam welding process within a frequency range of 0 Hz to 5 kHz has also shown a beneficial impact to the grain structure in the fusion zone. However, the main influencing factors and mechanisms behind this refinement effect are not completely understood in the case of the comparatively fast deep penetration laser beam welding. Within the scope of this research project this mechanisms and factors shall be determined by means of experimental investigations. The main assumption is that the refinement effect is more efficient for comparatively high frequencies and is mainly based on grain detachment due to the additional relative movement between the melt pool and the solidification front. Knowing the main influencing factors of this effect can provide a basis for the future development of efficient system technologies capable to produce a finer grain microstructure and hence improved weld seam properties, especially reducing the occurrence of hot-cracking.