Effect of detonation gun sprayed Cu–Ni–In coating on plain fatigue and fretting fatigue behaviour of Al–Mg–Si alloy

Detonation gun spray technique was employed to coat Al–Mg–Si alloy (AA 6063) specimens with Cu–Ni–In powder. Coated samples were characterized with reference to the microstructure, porosity, residual stresses, microhardness and surface roughness. Plain fatigue (without fretting) and fretting fatigue tests were carried out at room temperature on uncoated and coated specimens. The detonation gun spray process resulted in a dense coating of almost uniform deposition with low porosity (0.3%) and good adhesion between the substrate and the coating. Under plain fatigue loading 40 μm thick coated samples exhibited superior lives compared with uncoated and 100 μm thick coated specimens due to the presence of higher surface compressive residual stress in the former. Delamination-induced failure resulted in inferior lives of 100 μm thick coated specimens. Under fretting fatigue deformation 40 μm thick coated specimens exhibited superior lives compared with 100 μm thick coated samples owing to higher compressive residual stress at the surface and better interfacial adhesion. At 120 MPa stress level 40 μm thick coated specimens exhibited superior fretting fatigue life compared with uncoated sample and at stress levels above 120 MPa the converse was true. This was attributed to interface cracking at higher stress levels.