Because Zesuaium armor is nearly impossible to repair, most modern ships' armor plating is primarily composed of Yamataium, an artificial metalloid with self-healing molecular bonds. With guidance, the Yamataium can patch small to mid-size holes as needed in a matter of days.
Yamataium is regarded by many as the most advanced metallic alloy ever developed next to Zesuaium. Unlike Zesuaium, however, Yamataium is highly-resilient to damage (it will regenerate its strength over time) and to date is the only alloy capable of resisting the effects of particle disruptor beams effectively. It's very cost-prohibitive to produce and likewise, very expensive.
The Yamatai Star Empire considers Yamataium a restricted material and doesn't export it or allow its export. Only “Major Corporations” are allowed to make and use it under Yamataian law.