How to machine MIC-6 cast aluminum plate.

01 · Why MIC-6 vs 6061

Stability over strength.

6061 plate normally ships as T651 — solution-treated, quenched and stress-relieved by stretching — but the stretch only reduces the rolling and quench stresses. Heavily machined parts, especially thin or asymmetric ones, can still move as the remaining stress is released.

MIC-6 is fundamentally different. The molten aluminum is poured into a mold, slow-cooled in place, stress-relieved, and both faces are precision-milled at the mill. As a cast and stress-relieved product it has no rolling stresses, and internal stress is essentially zero from the casting process forward. The part stays where you put it. The trade-off: lower strength (~165 MPa UTS vs ~310 for 6061-T6) and slightly more porosity due to the cast structure. For optical mounts, metrology fixtures, and vacuum hardware, that’s a deal you happily make.

See our MIC-6 vs ATP-5 vs 6061 comparison for the broader trade-offs.

03 · Practical notes

Porosity is the unique consideration.

• ▸Tooling: uncoated polished carbide — same as 6061. Sharp edges with positive rake.
• ▸Coolant: water-soluble flood, MQL, or dry. MIC-6 generates clean chips like 6061.
• ▸Porosity: occasional small voids are inherent to cast plate. For optical, sealing, or vacuum-tight applications, plan around it — leave finish stock to clean up minor porosity, or specify ATP-5 (premium grade) for tighter porosity control.
• ▸Don’t machine deeper than the spec sheet allows: some MIC-6 grades have only ~0.060″–0.125″ of as-cast surface that’s machined off at the mill. Going deeper than that exposes raw cast structure that may have more porosity.
• ▸Anodize quality: generally good but not as clean as wrought 6061. For cosmetic-critical work, finish-machine to remove surface imperfections, then Type II anodize.
• ▸Don’t use MIC-6 for load-bearing parts: 165 MPa UTS is half of 6061. Optical mounts, fixtures, plates — yes. Brackets carrying real load — no, use 6061 or 7075.