Impression creep behavior of extruded Mg–TiO2 composites prepared by powder metallurgy

Abstract

Magnesium (Mg) composites with ceramic fillers are considered favorable for their recyclability compared to Mg alloys for lightweight designs with high creep resistance. In this work, we studied the difference in impression creep properties of pure magnesium and its composites, which contained 2, 3.5, and 5vol% of submicron TiO2 particles. For each composition, samples were fabricated by hot extrusion after hot pressing of the cold-compacted powders. Creep tests were conducted at temperatures in the 423–473K range and under stress levels in the 125–275MPa range. The results showed that the composites had higher creep resistance than pure magnesium, and increasing TiO2 content improved their creep behavior under all testing conditions. The effect of TiO2 content on grain size was statistically insignificant, and therefore, the improvement was attributed to reinforcing ceramic particles, which reduce the creep load on the magnesium matrix. The Dorn model was used in a new approach to calculate the effective stress on the magnesium matrix, justifying composites' higher creep load-bearing capacity than pure Mg under studied creep conditions. Fitting the Dorn exponential equation to creep data revealed that the stress exponent was between 6.6 and 8.6, and the activation energy was between 90.1 and 95.2kJ/mol for all compositions. Therefore, it was inferred that pipe diffusion-controlled dislocation climb was the creep mechanism for the studied materials.