Mechanical Properties and Wear Behavior of Aluminum Grain Refined by Ti and Ti+B

Grain refinement, by adding master alloys, is an important industrial process for aluminum casting operations. In this work, microstructure, microhardness, tensile properties, surface roughness and wear behavior of Al and both Al-0.15Ti and Al-0.05Ti-0.01B microalloys were investigated. The addition of Ti and B to pure Al reduced the grain size by 83%. The grain refinement effect was due to the presence of Al3Ti and TiB2 particles, which activated the columnar-to-equiaxed transition and improved both microhardness and tensile properties. The presence of both Al3Ti and TiB2 particles was confirmed using thermodynamic calculations. Average microhardness values increased form 39 HV for pure Al to 95 and 76 HV for Al-Ti and Al-Ti-B microalloys, respectively, by solid solution hardening. The enhanced wear behaviour of Al was due to the coarse-grained structure where the plastic deformation mechanism took place. Whereas, grain pull-out dominated the wear behavior of fine-grained specimens. It was concluded that the material with a smooth surface has high friction coefficient and low wear rate.