From LSWiki

Aperture: Alloy

Alloy focuses on the capacity of one's lens to be shaped into enduring objects, and more generally the capacity of light to interact with metal. This aperture enhancing one's constructs and ultimately gives one a greater leeway to interact with ferrous materials.

Primary Skill  : metal affinity

• Tier 1  : lesser smithing specialty access, access to the Repair volition
• Tier 2  : major smithing specialty access, access to the Empower and Balance volitions
• Tier 3  : greater smithing specialty access, increased tolerance to ferrous materials

Sadly, it seems like despite the description this does not grant your constructs or powers any further ability to interact with ferrous material based on metal affinity. At the very least, at 250 I was still seeing weapons and powers turned away from iron gear. It does let you wear adamantine full suit while wielding Strangmacht drunk on quicksilver! -Shinichi