Influence of ultrasonic amplitude and position in the vibration distribution on the microstructure of a laser beam welded aluminum alloy

Abstract

There are many reasons for influencing the laser beam induced weld pool. The manipulation of the dynamics, the solidification, the resulting grain size, and in the end, as a result of the aforementioned influencing, the mechanical characteristics of the weld is the aim of different attempts to gain an impact on the melt. Aluminum alloys tend to porosity formation because of different solubility of hydrogen in solid and liquid states. For reliable welds, the porosity has to be limited. An ultrasound excitation is one possibility to allow a fast degassing, especially for the considered round bars, for which no welding through is possible for geometric reasons. The presented research shows the influence of the ultrasonic amplitude on the microstructure of laser beam welded round bars of the aluminum alloy AA6082-T6. Furthermore, the position of the weld pool in the vibration distribution is varied and the influence evaluated. Metallographic cross sections show in analyses the resulting weld characteristic and the microstructure of the weld metal. The grain size and the grain orientation are evaluated for the different ultrasound parameters. Additionally, the summed porosity area is compared to acquire knowledge about the correlation between ultrasound excitation (with regard to vibration amplitude and position in the vibration distribution) and pore formation.

Influence of Ultrasound on Pore and Crack Formation in Laser Beam Welding of Nickel-Base Alloy Round Bars

“…Metals 2020, 10, x FOR PEER REVIEW 5 of 13 Table 3), for an ultrasonic amplitude of 6 µm only one welding test per wave position is conducted for testing the effects of excessive excitation, which effects spatter. The applied parameters were determined by previous experiments [4,12]. Metallographic cross sections of each specimen are prepared.…”

“…Hence, it can prevent segregation including its consequences and foster a finer grain structure, because dendrites break through mixing, which in turn creates more nucleation sites [3]. A finer grain structure improves strength as well as ductility and hardness [4]. In addition, porosity and hardness in the heat affected zone can be decreased and penetration depth can be increased for aluminium welds [5,6].…”

“…In result, a V-shaped weld seam collapse forms [11]. Experiments with similar setups showed that with laser beam welding sagging appears in the weld and the keyhole's bottom part can be closed by ultrasonic excitation [4,12]. The experiments in our contribution investigate the ultrasonic excitation effects on partial penetration laser welded nickel alloy round bars, see Table 1, to improve the weld properties and minimize pore and crack formation.…”

Influence of the ultrasonic vibration amplitude on the melt pool dynamics and the weld shape of laser beam welded EN AW-6082 utilizing a new excitation system for laser beam welding

“…The study concluded that grain refinement is caused by dendrite fragmentation. The influence of the ultrasonic amplitude on the weld seam properties has been investigated in [6]. The extent to which local excitation influences the weld seam was also investigated.…”

“…The local excitation depends on the excited vibration shape of the system and, in particular, on the relative position of the weld with respect to the vibration nodes and antinodes of the system. In [6], the situation where the melt bath is in a vibration anti-node (which means that the entire melt bath is shaken) was compared with the situation where the melt bath is in a vibration node (which means that the borders of the melt bath are expanded and compressed). The ultrasonic frequency used was 20 kHz.…”