Investigation into heat treatment and residual stress in laser clad AA7075 powder on AA7075 substrate

The laser cladding of AA7075 powder onto a AA7075 substrate was conducted to evaluate the effect of heat treatment and measure residual stress between the clad layer and substrate in order to better understand the effect of laser cladding. The microstructure formed in the clad region was characteristic of a high cooling rate, which is typical for laser cladding. The heat affected zone showed coarser precipitates when compared with the substrate and was attributed to the heating from the laser. A solution heat treatment followed by aging was employed to restore the strength in the heat affected zone. Nano-hardness traverses of the clad and substrate was performed and it was shown the hardness in the 7075 clad layer was lower than the substrate both pre and post heat treatment and was attributed to the vaporisation of zinc and magnesium. Neutron diffraction was employed to measure the residual stress pre and post heat treatment. The residual stresses formed in the clad layer were tensile and about 50 MPa in magnitude and the heat treatment increased them slightly to 100 MPa.