Microstructural features and cracking of laser cladding on 7xxx aluminium alloys with Al-12%Si powder

Increasing interest is to apply advanced laser technology for surface cladding on aluminium alloys or corresponding components, in order to repair the damaged surfaces caused by fatigue or corrosion and to restore the original properties. However, the mechanical or corrosion properties strongly depend on the microstructures. This paper presents the study of the microstructural features in both the clad layer and the Heat-affected zones (HAZs). The aluminium-12%silicon (Al-12%Si) was used for cladding on 7xxx series aluminium alloys.

The main features in the clad layer are fine α-aluminium columnar dendritic grains plus some interdendritic aluminium-silicon eutectic. There exit silicon particles between the dendrite arms. Silicon particles in eutectic are smaller and less angular. But the microstructure at the centre is considerably finer. Coarse grains occurred in the HAZs. Cu segregation occurred at both the grain boundaries and the grain interior, resulting in a Cudepleted α-phase next to a Cu-rich eutectic, forming dark strips-liquation film at the grain boundaries. The energy dispersive x-ray (EDX) spectrum indicated that the liquation film is copper-rich with other elements such as Fe, Zn and Mg elements (Al₂CuMg & Al₇Cu₂Fe particles). These liquation films are often associated with cracking and corrosion because of the brittleness.