ANTIFRICTION COATINGS ON ALUMINUM AND ITS ALLOYS FORMED BY ELECTRIC SPARK ALLOYING FROM POWDER MATERIALS

The effectiveness of the method of ESA with powder materials for the reinforcement of aluminum and its alloys may be linked with several factors. First, powder particles introduced into the electrode gap (EG) initiate discharges at a greater distance between the electrodes, and increasing the EG brings about a redistribution of the discharge energy in the anode-EG-cathode system such that the proportion of energy liberated on the electrodes decreases, while that liberated in the EG increases [5]. Secondly, the presence of powder particles in the EG results in the formation of a multichannel electric discharge structure [6], which divides a single erosion crater into a multitude of small craters. With the simultaneous decrease in energy liberation on the electrodes, the powder particles entering the discharge channel experience comminution with rapid melting and evaporation pulses, so that material transport to the basis is effected in the vapor, liquid, and solid phases. Relief forms mainly with the participation of the liquid phase because solid-phase particles seldom attach themselves firmly to the cathode surface. An electron microscopical examination of the microrelief on an aluminum cathode revealed long streaks of molten powder material and spreading of the liquid phase over the surface (Fig. i). Under these conditions the erosion of both electrodes was considerably reduced, with the anode being practically unconsumed and the volume erosion of the cathode being much smaller than the volume of the coating-forming powder material transported onto it. The effectiveness of the process of ESA of aluminum and its alloys was assessed in rubbing tests on coatings. A study was made of the effect of composition of the powder mixtures on the structure, thickness, hardness, and wear resistance of coatings. In these tests copper,