Effect of high-frequency beam oscillation on microstructures and cracks in laser cladding of Al-Cu-Mg alloys

This paper provides a new method to suppress solidification cracks in laser cladding of Al-Cu-Mg alloy by high-frequency beam oscillation without additional auxiliary measures. The effects of oscillation frequency on crack suppression were investigated by analyzing the microstructure evolution. The results show that the intercrystalline precipitated phase changed from coarse and continuous line to spiderweb-like morphology with the oscillation frequency ( f ) increased from 50 Hz to 500 Hz, and the thermal cracking tendency was completely reduced when the density of coarse intergranular precipitates was <300 μm/mm 2 ( f ≥ 200 Hz). The coarse Al 2 Cu and Al 0.92 Cu 1.08 Mg low-melting eutectic phases formed by the Cu element segregation between the columnar dendrites constituted the crack source and crack expansion channel. The rapid and periodic motion of a high-frequency oscillating laser can promote the uniform energy distribution and drive the melt flow, which will induce the columnar to equiaxed transition. The web-like eutectic liquid film between equiaxed dendrites has a smoother reflux channel and coordinated deformation ability. When the solidification shrinkage force pulls the local liquid film, the rest of the liquid phase can return to heal the crack in time, which is the main mechanism for the solidification cracks to be reduced. • A new type of oscillating laser cladding process is investigated. • Macroscopically well-formed Al-Cu-Mg alloy cladding layers are achieved by high frequency beam oscillation. • The fast-periodic motion of the oscillating laser beam can effectively suppress solidification cracks. • The mechanism of the columnar to equiaxed transition induced by beam oscillation is discussed.