Product Code: PIC06_307

Microstructural Features and Cracking of Laser Cladding on 7XXX Aluminium Alloys with Al-12%Si Powder
Authors:
Qianchu Liu, DSTO; Melbourne Australia
Presented at PICALO 2006

There has been increasing interest to apply laser cladding technology on aluminium alloys for repairing damaged surfaces of aircraft components by fatigue or corrosion. 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) powder was used for cladding of 7075 Al alloy. The main features in the clad layer are fine -aluminium dendritic grains plus some inter-dendritic aluminium-silicon eutectic. There exist silicon particles between the dendrite arms. Silicon particles in eutectic are smaller and less angular. The considerably finer dendritic structure is dominant at the centre but the columnar dendritic structure appears in the overlapping region. Coarse grains occur in the HAZs. Cu segregation occurs at both the grain boundaries and the grain interior, resulting in a Cu-depleted -phase next to a Cu-rich eutectic, forming dark strips-liquation film at the grain boundaries. The energy dispersive x-ray (EDX) spectrum indicates 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 because of the brittleness.