The Effect of Wire Feeding Speed on Solidification Cracking of CMT Welding for Al-Si Alloys

Abstract

In this work, a welding solidification crack sensitivity test platform was established to study the effect of wire feeding speed (WFS) on solidification crack sensitivity during cold metal transfer (CMT) welding for AA6061 aluminum alloy. The test results show that as the WFS increased from 4 m/min to 5.5 m/min, the sensitivity of the solidification cracks also increased. With a further increase in the value of the WFS, the crack sensitivity decreased and eventually ceased to exist. A new perspective of the microstructure and crack propagation mechanics model was applied to understand the effect of WFS on solidification cracks. With the use of scanning electron microscopy (SEM) and a high-speed camera, it was found that as the WFS increased from 4 m/min to 5.5 m/min, the microstructure of the grain size changed from bigger to smaller, and the stability of the crystal microstructure was reduced. The crack propagation mechanics model was changed, which promotes crack propagation, increasing by 233%. When the WFS continued to increase beyond 5.5 m/min, the size of the crystal structure changed from small to big, the stability of the crystal microstructure was increased, the crack generation was suppressed, and the cracking rate was significantly reduced.

Untitled

“…Besides, Huang et al [55] emphasized that increasing the WFS weakens the crack rate while increasing the welding speed increases the crack rate. The same conclusion came with Huang et al [56] as the authors realized that when the WFS exceeded 5.5 m/min, cracks were reduced as the size of the crystal microstructure increased. The mechanical state was stable, which suppressed the occurrence of cracks.…”

Solidification Cracking Restraining Mechanism of Al-Cu-Mg-Zn Alloy Welds Using Cold Metal Transfer Technique

“…Wojciech Stopyra et al [ 19 ] reported that reducing the content of silicon impurities in AA7075 powder could lower sensitivity to solidification cracking in laser powder bed melting. Huang et al [ 20 ] studied the effect of wire feeding speed on the susceptibility to solidification cracking in cold metal transfer (CMT) welding of AA6061 aluminum alloy, and they found that an increase in wire feeding speed first increased the solidification cracking susceptibility of the weld and then decreased it. For the perspective of the effect of the low-heat-input fusion welding method, especially the CMT technique, on the dendritic growth and solidification cracking susceptibility of the weld, more studies on the solidification cracking phenomenon in Al-Cu-Mg-Zn aluminum alloys in CMT welds are required.…”