Simultaneous enhancement of hardness and corrosion resistance in liquid-metal-dealloyed Mg–Ti composites via short-time Al-melt treatment

Abstract

This study presents a short-time reactive Al-melt treatment that simultaneously enhances hardness and corrosion resistance in liquid-metal-dealloyed Mg–Ti composites. A three-dimensional bicontinuous Mg–Ti composite is first fabricated by immersing a Ti 30 Cu 70 precursor in a pure Mg melt, followed by immersion in a pure Al melt at 750 °C for 10 s. The initial Mg–Ti composite consists of a co-continuous α -Mg/ α -Ti matrix–matrix structure. After Al-melt treatment, the interconnected morphology is preserved, while the phase constitution is reconstructed into a multiphase α -Ti/TiAl 3 /Al 3 Mg 2 structure. TiAl 3 forms along the residual α -Ti ligaments, whereas the original Mg-rich regions transform into Al 3 Mg 2 . The average effective grain size of the residual α -Ti decreases from 3.7 to 0.8 µm, accompanied by increased local misorientation and a higher density of {11–22} compression twin boundaries. As a result, the surface hardness increases from 106 to 378 HV, while remaining above 260 HV at a depth of 260 µm. The Al-treated Mg–Ti composite also exhibits a markedly reduced corrosion rate in 3.5 wt.% NaCl solution, decreasing from 13.2 to 0.5 mm/year based on hydrogen evolution measurements and from 17.2 to 0.7 mm/year based on weight-loss measurements. Scanning Kelvin probe force microscopy reveals that the initial direct α -Mg/ α -Ti interface, with a Volta potential difference of approximately 635 mV, is replaced by α -Ti/TiAl 3 and TiAl 3 /Al 3 Mg 2 interfaces with lower potential differences of approximately 271 and 285 mV, respectively. Overall, the short-time Al-melt treatment enables simultaneous hardness increase and corrosion mitigation through rapid interfacial reconstruction and phase transformation while preserving the bicontinuous structure.