Structure and tribological properties of cast aluminum matrix composites modified with calcium

The influence of calcium modifying additive in the amount from 0.05 to 0.3 wt.% on the microstructure formation and change of tribological properties of cast composite materials based on the pseudo-binary Al – Mg2Si system (15 and 25 wt.%) has been studied. It is shown that with the increase of calcium content in Al – 15Mg2Si composites, the average size of Mg2Si reinforcing particles (measured by Feret diameter) decreases slightly from 32.69 μm at 0.05 wt.% Ca to 30.13 μm at 0.25 wt.% Ca; however, the degree of particle distribution uniformity in the composite structure improves significantly (from 0.69 to 0.58, respectively). In the Al – 25Mg2Si composites at 0.25 wt.% Ca, the average Feret diameter of Mg2Si particles is approximately 30 μm, with a roundness index of 0.48 and a distribution uniformity index of 0.33, which is quite a good value. Further increase of Ca content up to 0.3 wt.% leads to an increase in the average size of the Mg2Si particles up to 35.16 μm and a deterioration of the distribution uniformity index to 0.41. According to the results of tribological tests on the pin-on-disc scheme in a pair with steel in conditions of dry friction, the friction coefficient and mass wear of the samples of Al – 15Mg2Si cast aluminum matrix composites modified with calcium (0.25 wt.% Ca) averaged 0.383 and 0.0071 g, respectively; for Al – 25Mg2Si under the same conditions, it was 0.423 and 0.0051 g. At the same time, in the unmodified state for Al – 15Mg2Si, mass wear was 0.0357 g at a friction coefficient of 0.4667, and for Al – 25Mg2Si it was 0.0131 g and 0.4623, respectively. The results confirm that calcium modification allows to significantly improve the microstructure of cast aluminum matrix composites of Al – Mg2Si system, which provides increased wear resistance and expands the possibilities for their application in conditions of intensive friction. The research was funded by the Russian Science Foundation (Project № 20-19-00687-П, https://rscf.ru/project/23-19-45019/).