Fabrication and mechanical properties of pressureless melt infiltrated magnesium alloy composites reinforced with TiC and Ti2AlC particles

Herein we report on the fabrication and mechanical properties of Mg composites fabricated by pressureless melt infiltration of Mg and Mg alloys into porous preforms of TiC and Ti2AlC. The latter is a member of the MAX phases – viz. layered, machinable, ternary carbides and nitrides – some of which are relatively light and stiff. In this study, pure Mg and three, commercially available, aluminum-containing Mg alloys – AZ31, AZ61 and AZ91 – were used as matrices at a loading of ≈50vol%. For the most part, increasing the Al content enhanced the elastic moduli, Vickers hardness values and yield and ultimate compressive strengths. Reducing the particle sizes of the TiC and Ti2AlC particulate reinforcements also had a large impact on the mechanical properties. At 1028±5MPa, the ultimate compressive strength of a TiC–AZ61 composite, in which the TiC particle size distribution is Lorentzian and centered at, dc=0.41±0.01µm, was ≈40% higher than that of the same composite with coarser TiC particles with a bimodal size distribution centered around dc=1.6±0.1µm, and 5.8±0.3µm. In addition, the elastic modulus and Vickers hardness of the former composite were measured to be 174±5GPa and 3.4±0.3GPa, respectively. For the Ti2AlC reinforced composites, the best properties were obtained when AZ61 was reinforced with Ti2AlC particles with dc=0.51±0.01µm. The enhancements in elastic and mechanical properties are attributed to the presence of a strong interface mediated by the presence of Al in the matrix, finer reinforcement particle sizes and finer grained Mg-matrices. The Ti2AlC composites are slightly lighter and can be fabricated at lower temperature than comparable TiC composites; the former are also readily machinable but more expensive.