Influence of Continuity of Electric Spark Coatings on Wear Resistance of Aluminum Alloy

The replacement of ferrous metals with lighter non-ferrous ones, in particular with aluminum and its alloys, is of great importance for reducing the specific material consumption of products. Modification of aluminum alloy D16 with combined electro spark coating VK8 + Cu is considered. Based on the method of finite element analysis of the Nastran software complex, an optimal coating continuity was determined at the level of 55 - 65%, which provides efficient workability of the coating via reducing the residual stresses in the base and tangent stresses in the plane of adhesive contact, optimization of the coating continuity, distribution of contact loads, and formation of optimal surface geometry. The results of modeling the stress-strain state of the coating-base at a coating continuity of 60% and a normal load of 600 N indicate a 30 MPa increase in equivalent stresses in a unit element of the coating and a decrease of this parameter by 100 MPa in the base as compared with an unmodified D16 surface, indicating the localization of normal stresses mainly in the combined coating. It was experimentally established that at a combined coating continuity of 60%, reduction of D16 wear by 2 times and decrease in the average power of acoustic emission by 1.33 times are provided, which testifies to the efficient structural adaptability of the coating-base under friction. The mechanisms of increasing the wear resistance of the VK8 + Cu coating according to the rheological-kinetic model, which reflects the correlation between processes of fracture and deformation under friction, are considered. It is determined that the high wear resistance of the combined coating is due to the combination of rheological properties of hard alloy VK8 with a fracture toughness of 13.2 MPa·m1/2 and plastic copper material with a fracture toughness of 100 MPa·m1/2, which contributes to the efficient relaxation of stresses under friction.