钛合金激光立焊烧穿和气孔缺陷及其数值模拟

Burn through holes and porosities during laser welding of titanium alloy in vertical position and their numerical model

采用在平焊优化过的激光焊接参数对钛合金进行立焊,立向上焊时烧穿倾向较大,气孔倾向较小;立向下焊时烧穿倾向较小,气孔倾向较大.基于体积分数法(VOF)建立了追踪小孔界面的数值计算模型模拟小孔和熔池流动行为,分析了焊接位置对激光立焊烧穿和气孔倾向的影响机制.结果表明,立向上焊时焊接方向与重力相反,小孔所受静水压力较小,小孔易于长大,小孔空腔所需的液态金属得不到有效补充,烧穿倾向增加.立向下焊时焊接方向与重力一致,小孔振荡导致崩塌卷气,所生成的气泡缺乏逸出通道,气孔倾向增加.

Titanium alloy plates were welded by laser under vertical positions with the optimized parameters obtained by flat welding positions.For vertical up(VU)welding,burn through holes occurred while the porosity was low.For vertical down(VD)welding,burn through holes didn’t occur while the porosity was high.With volume of fraction(VOF)method,a numerical model was established to track the interface of keyhole,which helped to understand the effect of welding positions on burn through holes and porosity.During VU welding,the welding direction was opposite to gravity,and the hydrostatic force on keyhole was small.The keyhole was easy to be expanded.When the liquid metal could not fill in the cavity of keyhole in time,burn through holes occurred.During VD welding,the welding direction was the same as gravity.The oscillation of keyhole size resulted to the collapse of keyhole and the entrapment of gas.Since there was lack of escape ways for entrapped gas,porosity increased during VD welding.