Fluid Flow Characteristics and Porosity Behavior in Full Penetration Laser Welding of a Titanium Alloy

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• 作者：Baohua Chang ; Chris Allen ; Jon Blackburn…
• 刊名：Metallurgical and Materials Transactions B
• 出版年：2015
• 出版时间：April 2015
• 年：2015
• 卷：46
• 期：2
• 页码：906-918
• 全文大小：2,642 KB
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• 刊物类别：Chemistry and Materials Science
• 刊物主题：Chemistry
  Materials Science
  Manufacturing, Machines and Tools
  Metallic Materials
  Operating Procedures and Materials Treatment
  Characterization and Evaluation Materials
  Numerical and Computational Methods in Engineering
  
• 出版者：Springer Boston
• ISSN：1543-1916

文摘

In this paper, a computational fluid mechanics model is developed for full penetration laser welding of titanium alloy Ti6Al4V. This has been used to analyze possible porosity formation mechanisms, based on predictions of keyhole behavior and fluid flow characteristics in the weld pool. Numerical results show that when laser welding 3?mm thickness titanium alloy sheets with given laser beam focusing optics, keyhole depth oscillates before a full penetration keyhole is formed, but thereafter keyhole collapses are not predicted numerically. For lower power, lower speed welding, the fluid flow behind the keyhole is turbulent and unstable, and vortices are formed. Molten metal is predicted to flow away from the center plane of the weld pool, and leave a gap or void within the weld pool behind the keyhole. For higher power, higher speed welding, fluid flow is less turbulent, and such vortices are not formed. Corresponding experimental results show that porosity was absent in the melt runs made at higher power and higher welding speed. In contrast, large pores were present in melt runs made at lower power and lower welding speed. Based on the combination of experimental results and numerical predictions, it is proposed that porosity formation when keyhole laser welding may result from turbulent fluid flow behind the keyhole, with the larger the value of associated Reynolds number, the higher the possibility of porosity formation. For such fluid flow controlled porosities, measures to decrease Reynolds number of the fluid flow close to the keyhole could prove effective in reducing or avoiding porosity.