EROSION OF A STRONG ALUMINUM-ALLOY

The erosion of a strong aluminum alloy (7075-T6) and annealed commercially pure aluminum was modelled with impacts by ball bearings of diameter 5 mm at velocities of 140-185 m s-1. Single impacts caused significant erosive loss only at low impact angles (20°-35°). Single impacts normal to the surface removed negligible amounts of metal. Erosion by impacts normal to the surface occurred only when the deformation field from one impact overlapped that of an earlier impact. Erosion resistance, as measured by velocity threshold for weight loss, was much lower for the high strength 7075-T6 alloy than for pure aluminum. Thus alloying for strength diminishes erosion resistance. Treatments that improve the fracture toughness of the 7075 alloy did not improve erosion resistances. Metal left the target as one or two chips per impact. These separated along narrow bands of intense shear. While particle impacts always deform the surface, it is postulated that this deformation results in metal loss (erosion) only when a shear instability (adiabatic shear) develops under the ball prior to the tensile stresses set up in the surface upon particle rebound. © 1979.