Variable-density composite articles, preforms and methods

A metal matrix composite article, comprising:

• a cast, reinforced body, the body comprising a first region and a second region, the first region having more reinforcement than the second region;
• a first reinforcement component;
• a second reinforcement component;
• a metal matrix composite material occupying the second region of the body and comprising a metal matrix material and the second reinforcement component;
• a preform positioned in the first region of the body and infiltrated by at least the metal matrix material of the metal matrix composite material, the preform comprising
• a first end,
• a second end,
• an outer surface,
• the first reinforcement component, the first reinforcement component comprising a density increasing between the first end of the preform and the second end of the preform according to a first gradient, and
• a porous structure configured to allow passage of the metal matrix material into the preform and to block or reduce passage of the second reinforcement component into the preform;
• and
• a transition region of the body located outside the preform and proximate the outer surface of the preform, the transition region comprising a distribution of the second reinforcement component adjacent to the outer surface of the preform, the distribution of the second reinforcement component comprising a density increasing according to a second gradient in a direction toward the outer surface of the preform.