Fused Hillwen Alloy is crafted with Hillwen Engineering in Mabinogi. This page lists everything needed to make it, checked against the game as it exists today. The interactive planner lives in the Hillwen Companion.
Recipe availability
Fused Hillwen Alloy is a rank 9 Hillwen Engineering recipe with a best success rate of 95% at rank 1 and dan ranks.
Materials
Each craft uses
50× Hillwen Alloy
20× Intact Shyllien — Seal Merchant Mondays 20 for 30 seals (once a week), auction house, or Magic Craft rank A