Study on Surface Layers of Aluminum and Titanium Alloys and Analysis of their Scuff Resistance

Abstract

To reduce the risk of scoring copper or zinc coatings were applied to the samples in molten salts at a temperature of 350-500°C. Using ion sputtering and Auger electron spectroscopy the depth of the surface layers and the grain size in the coating were determined. Samples were plates 0.5-0.7 mm thick made of titanium and aluminum alloys. For copper-coated alloys a coating zone up to 10 μm and a diffuse zone up to 6 μm which is intermediate between the coating and the substrate can be distinguished in the surface layers. For zinc-coated aluminum alloys there is one zone of 5-7 μm which is an aluminum-zinc alloy of variable composition across depth. Thus, a soft metal formed on the surface of the titanium and aluminum alloys when processed in the salt melt is connected to the base metal with metallic bonds. Moreover, the higher the temperature and the longer the holding time in the salt melt, the thicker the coating is. While investigating the score resistance a dependence of the friction moment change on the path travelled to a score appearance was obtained. It has been established that the score resistance of the titanium and aluminum alloys is directly dependent on the inhomogeneity factor which is sharply increased when there is a softer (compared with the base metal) coating on the surface of the metal processed. Experimental stamping-drawing of cups made of the titanium alloy workpieces preliminary copper-coated in the salt melt was carried out. The production cycle was significantly reduced, and the surface quality of the products after the coating removal was high, the scoring was not observed. Thus, the use of soft (compared with the base metal) metal coatings applied in salt melts is promising for titanium and aluminum alloys.